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\chapter{24}{Intersections and Signal Control}
\label{volume:infrastructure:chapter:intersections-and-signal-control}
% @ guide/24-intersections_and_signal_control/intersections-and-signal-control.src: lines 1-5: code points 1-35

\quotation{A bland smile is like a green light at an intersection, it feels good when you get one, but you forget it the moment you’re past it.}{Douglas Coupland, novelist, 1961–}
% @ guide/24-intersections_and_signal_control/intersections-and-signal-control.src: lines 3-5: code points 1-35

The objective of this chapter is to equip the reader with tested practical knowledge to design and evaluate the layout and operation of intersections along BRT corridors. Intersections can cause significant delays in BRT operations, particularly by hindering station access, and they are the points where the BRT project has the largest perceived impact on mixed traffic and walking.\par
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An important strategy to improve the performance of intersections to better accommodate public transport, pedestrians, and other vehicles is to restrict general-traffic turning movements at intersections. \emphasis{The} \emphasis{BRT} \emphasis{Standard} awards up to 7 points for good handling of BRT movements through intersections, with the most points given to systems that prohibit all turns across the busway.\par
% @ guide/24-intersections_and_signal_control/intersections-and-signal-control.src: lines 12-15: code points 1-75

\tabletitle{1}{BRT Standard:Intersection Treatments}
\label{chapter:intersections-and-signal-control:table:brt-standardintersection-treatments}
\halign to 30\tablemodule{%
	\vtop{\sffamily\footnotesize\noindent\hsize=24\tablemodule#}\hbox to 0.5\tablemodule{}&
	\hbox to 0.5\tablemodule{}\vtop{\sffamily\footnotesize\noindent\hsize=5\tablemodule#}\cr
	\color{gray75}\bfseries \highlight{Treatment}& \color{gray75}\bfseries \highlight{POINTS} \cr
	\noalign{\vskip 1mm} \hline \noalign{\vskip 2mm} 
	\color{gray50}Turns prohibited across the busway&
	\color{gray50}7\cr
	\noalign{\vskip 2mm 
}	\color{gray50}Signal priority at intersections&
	\color{gray50}2\cr
	\noalign{\vskip 2mm 
}	\color{gray50}No intersection treatments&
	\color{gray50}0\cr
	\noalign{\vskip 2mm 
}}
% @ guide/24-intersections_and_signal_control/intersections-and-signal-control.src: lines 17-30: code points 1-9

This chapter also discusses the placement of stations relative to intersections along the corridor and the treatment of public transport vehicle turning movements, which are desirable to have but can also harm an intersection’s performance. Other elements of intersection treatments that are discussed include: signal prioritization technology for public transport vehicles, priority in roundabouts, narrow sections with mixed traffic, and techniques for keeping pedestrians and cyclists safe.\par
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Definitions that pervade the whole chapter are laid out in the first section; the second section covers the general approach to intersection problem solving; and the subsequent sections discuss different tools to improve intersection efficiency, particularly when grade separation is available.\par
% @ guide/24-intersections_and_signal_control/intersections-and-signal-control.src: lines 38-40: code points 1-84

\section{1}{Basic Concepts}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 3-625: code points 1-0

\quotation{Change means movement. Movement means friction. Only in the frictionless vacuum of a non-existent abstract world can movement or change occur without that abrasive friction of conflict.}{Saul Alinsky, political activist, 1909–1972}
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\subsection{1}{About Intersections}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:about-intersections}
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		\fignote{1}{The conflict between vehicles in a Y junction indicates that this is an intersection.\label{chapter:intersections-and-signal-control:figure:the-conflict-between-vehicles-in-a-y-junction-indicates-that-this-is-an-intersection}}{Elebeta.}
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		\fignote{2}{A channeled Y junction without conflicts does not have the basic element that defines an intersection.\label{chapter:intersections-and-signal-control:figure:a-channeled-y-junction-without-conflicts-does-not-have-the-basic-element-that-defines-an-intersection}}{Elebeta.}
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		\fignote{3}{Separated-grade solutions can eliminate intersections.\label{chapter:intersections-and-signal-control:figure:separated-grade-solutions-can-eliminate-intersections}}{Elebeta.}
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		\fignote{4}{Depending on space restrictions, separated-grade solutions may not eliminate intersections.\label{chapter:intersections-and-signal-control:figure:depending-on-space-restrictions-separated-grade-solutions-may-not-eliminate-intersections}}{Elebeta.}
	}
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The intersection is the area where two or more roads meet each other. The use of the word in Traffic Engineering technical language implies “roads for vehicles” and “at the same level,” but very often the expressions “at-grade intersections” or “single-grade intersections” are used to demonstrate the same concept. For flyovers and underpasses the term used is “interchange” or “separated-grade interchange.” When more than one mode is involved, the common traffic engineers’ wording is “crossing” as in “pedestrian crossing” (one of the roads is assumed to be a roadway); recently the term \emphasis{multimodal intersection} has also been applied.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 21-27: code points 1-22

By this definition, an intersection implies conflicts of vehicles attempting to use the same space and can refer to a unidirectional T-shaped or Y-shaped confluence area. The conflict in this area becomes clear as there is not enough space to accommodate the two incoming flows as they move into the exiting stream in a congested situation (Figure 24.1). Conversely, a channeled Y-shaped junction may not be an intersection (Figure 24.2).\par
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Because the majority of cases where two or more roads meet include many possible turning movements (not all conflicting), intersections can be seen as linking several other adjacent intersections as well—that is, an intersection is a larger conflict area that is composed of smaller conflict areas (or smaller intersections).\par
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Footpaths (or “roads for people”) are more important to accessibility in populated areas, therefore roadways are usually constructed between footpaths. When two roadways meet, several walkway crossings are needed. So a multimodal intersection encompasses a larger area than just the roadways where people conflict in trying to use the same space. (To keep things in perspective, let us remember that drivers and passengers are people.)\par
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The more conflicts there are in an intersection or in a crossing, the greater amount of time people will need to cross it safely. If there is a low frequency of vehicles arriving at the intersection where pedestrians, cyclists, or other vehicles want to cross, then those wanting to cross can do so safely without compromising travel time by what is known as “passage negotiation,” or waiting until the way is clear to cross. If over the years the vehicle frequencies throughout the day rise to the point where queues occur frequently or with enough intensity that the time required for pedestrians to cross safely becomes too long, then this is the moment to intervene.\par
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An intervention is justified by comparing the present value for the cost of its implementation, maintenance, and operation against the present value of its benefits. Time savings is the easiest to assess of these benefits, assuming a safe operation and that costs are directly related to benefits, such as fuel consumption and pollution.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 54-57: code points 1-14

Interventions start with zebra crossings and yield signs. Larger interventions involve channeling the vehicles and creating refuge islands. These are methods to clearly divide an intersection into several smaller components, improving traffic safety and reducing the overall delay; roundabouts or mini-roundabouts are ways to channel vehicles as well. Above a certain threshold for throughput, traffic lights are required, and their integration into intersections may grow in really complex ways to accommodate all conflicts. To accommodate still more throughput, methods to divert traffic and restrict direct movements come into play, until finally grade separation of the conflicting flows becomes necessary.\par
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In theory, a separated-grade traffic solution eliminates intersections (Figure 24.3), but in practice, due to space restrictions, intersections can also remain (Figure 24.4).\par
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\subsection{2}{General Concepts}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:general-concepts}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 70-258: code points 1-91

The concepts we present here are mostly about understanding the equations related to delay and queue sizes in signalized intersections, but note that these sections are not meant to be a comprehensive reference for these issues. The reader may want to further investigate the concepts of traffic density and traffic headway and how they relate to average traffic speed and flow. We provide further references for traffic signals in the bibliography.\par
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We emphasize that when applying formulas attention should be given to units and unit conversions. The appropriate unit of time to observe phase times in traffic lights is the second, which can be used to observe the time to walk or ride a few blocks; meanwhile, we better perceive speeds in kilometers per hour (kph) or alternatively in miles per hour (mph). It is useful to remember that 1 hour is the same as 3,600 seconds and 1 mile is approximately 1.6 kilometers and 1 kilometer is approximately 0.6 miles.\par
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\subsubsection{1}{Cross-Traffic Turn and Curbside Turn}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:general-concepts:subSubSection:cross-traffic-turn-and-curbside-turn}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 84-115: code points 1-88

For this chapter we have excluded the expressions “right turn” and “left turn” because they have different meanings in differently oriented systems. We have chosen to adopt “cross-traffic turn” and “curbside turn” instead.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 86-88: code points 1-14

\highlight{Cross-Traffic Turn:} a vehicle movement to exit the current traffic stream direction that requires crossing the opposite-direction traffic flow. If a busway or a bike lane is present near the median, there is also conflict with BRT vehicles or bicycles going straight in the same way and in the opposite way.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 90-93: code points 1-13

\highlight{Curbside Turn:} a vehicle movement to exit the current traffic stream direction that normally does not cross any vehicle flow. This movement conflicts with people on the sidewalk in both ways and, if the road is parallel to a curbside busway or a curbside bike lane, there is a conflict with that traffic as well.\par
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\highlight{U-Turn:} a vehicle movement to join the traffic stream travelling in the opposite direction of the vehicle’s current flow. Depending on the width of the median this movement can be less conflicting than the cross-traffic turn or more conflicting, since the speed has to be lower to make a U-turn. For this reason, U-turns are sometimes prohibited at existing intersections and promoted away from the intersection by creating another intersection exclusively for the U-turn. Due to road geometry restrictions or other considerations, this movement may eventually be channeled to start from a waiting area from the curb side of the road as shown by the pink car in Figure 24.5, in which case it will conflict with both flows in the same way that a cross-traffic turn from a perpendicular street would.\par
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		\img{\hsize}{infrastructure/assets/30f88cb26ecfc079be523ce4d1137a86fdba8dfb.png}
		\fignote{5}{Example of a cross-traffic turn (green car), a curbside turn (blue car), a U-turn without space (red car), and a U-turn with space (pink car) for right-hand-oriented driving in China, the United States, Brazil, and most of Europe.\label{chapter:intersections-and-signal-control:figure:example-of-a-cross-traffic-turn-green-car-a-curbside-turn-blue-car-a-u-turn-without-space-red-car-and-a-u-turn-with-space-pink-car-for-right-hand-oriented-driving-in-china-the-united-states-brazil-and-most-of-europe}}{Elebeta.}
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		\fignote{6}{Example of a cross-traffic turn (green car), a curbside turn (blue car), a U-turn without space (red car), and a U-turn with space (pink car) for left-hand-oriented driving in India, Indonesia, South Africa, Tanzania, Australia, and the United Kingdom.\label{chapter:intersections-and-signal-control:figure:example-of-a-cross-traffic-turn-green-car-a-curbside-turn-blue-car-a-u-turn-without-space-red-car-and-a-u-turn-with-space-pink-car-for-left-hand-oriented-driving-in-india-indonesia-south-africa-tanzania-australia-and-the-united-kingdom}}{Elebeta.}
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\subsubsection{2}{Speed}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:general-concepts:subSubSection:speed}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 117-137: code points 1-92

For the application of the concepts outlined in this chapter, speed is defined as the average traffic speed of all vehicles in a segment, for which we use the letter \emphasis{V }that is derived from the word velocity. Speed is measured by the mean time of all vehicles crossing the segment divided by the segment extension. Under our modeling intents (or capacity evaluation) it can be imagined that all vehicles are moving at that speed.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 119-123: code points 1-11

Still, when looking at the broader concept of speed—the ratio of motion expressed in distance per unit of time—it is useful to remember that for a given segment distance (Dsegment), knowing the speed (Vsegment) is equivalent to knowing the travel time it takes to make it through the segment (Timesegment) and vice versa, as the equivalent equations show:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 125-128: code points 1-40

Eq. 24.1\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 130-130: code points 1-8

$ V_\text{segment} = {D_\text{segment} \over \text{Time}_\text{segment}} \leftrightarrow \text{Time}_\text{segment} = {D_\text{segment} \over V_\text{segment}} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 132-132: code points 1-163

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 134-135: code points 1-0

\begin{itemize}
\item $ V_\text{segment}$: Velocity of the segment;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 135-136: code points 1-0
\item $ D_\text{segment}$: Segment distance;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 136-137: code points 1-0
\item $ \text{Time}_\text{segment} $: Travel time it takes to make it through the segment.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 137-137: code points 1-92
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 135-137: code points 1-92

\subsubsection{3}{Delay}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:general-concepts:subSubSection:delay}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 139-143: code points 1-84

Delay is the additional travel time, if not explicit, that is added onto the base reference of travel time, which is an ideal situation without any conflicts where the passenger, pedestrian, or driver is the only user of the road (no other drivers, pedestrians, users, or traffic lights).\par
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\subsubsection{4}{Passenger Car Unit (pcu)}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:general-concepts:subSubSection:passenger-car-unit-pcu}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 145-156: code points 1-38

A passenger car unit, or pcu, is a reference used to standardize different vehicle types by a common denominator. The conversion factor from a certain type of vehicle to a passenger car unit depends on the application intended after the conversion, when it is eventually calibrated for a specific use in a given situation. For example, this could be when consideration is given to the stress placed on the pavement or the potential of added congestion. Other considerations include whether the setting is an urban environment or along a highway, on a ramp, or in plain terrain.\par
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In general, a motorcycle, for instance, tends to have an equivalent of less than one vehicle, and a mini-bus is equivalent to more than one vehicle; the larger and heavier the vehicle, the higher the number of vehicles to which it is equivalent.\par
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\subsubsection{5}{Flow}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:general-concepts:subSubSection:flow}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 158-182: code points 1-84

Traffic engineering borrows concepts from fluid mechanics and uses “flow rate” as a measure of traffic intensity. From that definition, the word \emphasis{rate} is commonly dropped and “flow” alone is treated as the physical quantity expressed by the number of vehicles crossing a transversal section (or cross section, like a stop line) during a certain time interval. Flow is usually represented by the letter \emphasis{q} in equations, but we will avoid that here and use the full word instead.\par
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It should be noted that the use of the word \emphasis{volume} to express the same idea is accepted, despite being far from the original definition conceptually (in fluid mechanics the original comparative terms are \emphasis{volume flow rate} and \emphasis{mass flow rate}; the latter is more an appropriated reference as the vehicles can be somewhat compressed). Volume should refer to the total number of vehicles in the same way a liter refers to volume and liters per second refers to flow in hydraulics. The term is especially common in the expression “volume\slash{}capacity ratio.”\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 166-171: code points 1-39

Eq. 24.2\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 173-173: code points 1-8

$ \text{Flow}_\text{vehicles} = {Number_\text{vehicles} \over \text{Time}} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 175-175: code points 1-78

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 177-178: code points 1-0

\begin{itemize}
\item $ \text{Flow}_\text{vehicles} $: Number of vehicles crossing a transversal section (or cross section, like a stop line) per a given time;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 178-180: code points 1-0
\item $ \text{Number}_\text{vehicles} $:Number of vehicles;Time = Length of time the flow of vehicles is measured.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 180-180: code points 1-116
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 178-180: code points 1-116

Flow can also be expressed for pedestrians, bicycles, or even passengers (per hour).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 182-182: code points 1-84

\subsubsection{6}{Capacity and Saturation}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:general-concepts:subSubSection:capacity-and-saturation}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 184-253: code points 1-43

The capacity (flow rate) of a segment is given by the lower capacity of a section within it, and the term \emphasis{bottleneck} for the lower-capacity section expresses this concept quite well.\par
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The capacity of a section is defined as the maximum flow a section can handle under prevailing use. It is subject to the number of lanes, width of lanes, ramp inclination, cultural driving behaviors, and the use of surrounding areas, such as parking and stopping regulations, the presence of an intersection or traffic light ahead, and the existence and frequencies of bus stops.\par
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Capacity can easily and objectively be measured, but some of the influential factors listed above cannot. Many models have been developed to improve the forecast of road capacity based on the knowledge of design and use of surroundings, but even the more detailed simulators need careful calibration to correctly represent driver behavior differences that tend to be unique to each place.\par
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The simpler models do not commonly fit exactly to theories, either, and they are usually adjusted by experimental evidence. These models resort to the concept of \highlight{basic saturation flow}.\par
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Basic saturation (flow rate) is the capacity for a section of a given standard ideal roadway, divided by the number of lanes of that given standard roadway. It is commonly expressed by “s0.”\par
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Capacity and speed are interdependent and the maximum flow does not happen when speeds are at their highest. This is because the distance a driver maintains from another vehicle in front of him or her increases more proportionally than the speed increases. In a section of unconstrained road, the maximum speed capacity occurs between 60 and 80 kilometers per hour.\par
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Based on extensive observations, capacity models then define a way to forecast a \highlight{saturation flow} by multiplying the basic saturation flow by adjustment factors to account for various nonideal geometric, traffic, and environmental conditions of a given section, such as the number of lanes, lane width, presence of heavy vehicles, grade, parking facilities, bus blockage, area type, turning traffic along the segment, radius of turnings, pedestrian crossing traffic, but not considering traffic lights.\par
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Saturation is commonly written as “S” in equations, but here we use “SaturationFlow” to avoid confusion with demand saturation level, usually “X,” which represents the relationship between demand and capacity for a given infrastructure element such as an intersection or a station.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 216-218: code points 1-72

Eq. 24.3\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 220-220: code points 1-8

$ \text{Saturation}_\text{Flow} = \text{basicsaturationflowperlane}*NLanes*(f_\text{geometry}*f_\text{traffic}*f_\text{parking} * f \ldots) $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 222-222: code points 1-143

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 224-225: code points 1-0

\begin{itemize}
\item $ \text{SaturationFlow} $:Maximum flow a section can handle under prevailing use;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 225-226: code points 1-0
\item $ \text{basicsaturationflowperlane} $: Capacity of a given standard ideal roadway section;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 226-227: code points 1-0
\item $ \text{NLanes} $: Number of lanes;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 227-228: code points 1-0
\item $ f_\text{geometry} $: Adjustment factor to account for nonideal geometric conditions;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 228-229: code points 1-0
\item $ f_\text{traffic} $: Adjustment factor accounting for nonideal traffic conditions;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 229-230: code points 1-0
\item $ f_\text{parking} $: Adjustment factors to account for nonideal parking conditions;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 230-231: code points 1-0
\item $ f\ldots $: Other adjustment factors to account for various nonideal conditions.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 231-231: code points 1-89
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 225-231: code points 1-89

Saturation (flow rate), therefore, is the capacity of a section that is \highlight{not} under the influence of a traffic light. For a section that approaches a traffic light, saturation is the capacity assuming a constant green, which would equal the flow observed during the queueing discharge (after allowing a few seconds for the flow to become regular again). For this reason saturation may be called discharge (flow rate). When working in a specific location, the saturation of sections can be measured, so the resulting product of all these factors is known.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 233-238: code points 1-48

As a practical rule, even slightly distorting the concept of ideal conditions for urban environments will yield an observed saturation of 1,800 pcu\slash{}hour for a lane. For the purpose of capacity, measuring an 18-meter articulated bus is equivalent to 2.5 pcu. So in a busway the saturation per lane is 720 articulated buses per hour.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 240-243: code points 1-15

Eq. 24.4\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 245-245: code points 1-8

$ \text{SaturationFlow}=\text{CapFlow}_\text{away-from-intersectioni} = \text{saturationflowperlane} * \text{NLanes} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 247-247: code points 1-120

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 249-250: code points 1-0

\begin{itemize}
\item $ \text{SaturationFlow} $: Maximum flow a section can handle under prevailing use;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 250-251: code points 1-0
\item $ \text{CapFlow}_\text{away-from-intersection} $: Maximum flow of a section away from an intersection;saturationflowperlane = Maximum flow a given lane can handle;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 251-253: code points 1-0
\item $ \text{NLanes} $: Number of lanes.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 253-253: code points 1-43
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 250-253: code points 1-43

\subsubsection{7}{Continuity}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:general-concepts:subSubSection:continuity}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 255-258: code points 1-91

Although no direct formula application about continuity is used in this chapter, one basic property of an intersection is that all the flow into the intersection has to exit the intersection.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 257-258: code points 1-91

\subsection{3}{Traffic Signal Concepts}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 260-625: code points 1-0

Traffic lights are a very common intersection management tool in business districts where the BRT corridor design is likely to face more challenges. Traffic light controllers can be coordinated and actuated (use detection) by utilizing more or less complex technology and algorithms. A lot of research and progress has been made in the past thirty years, but the practical use of the research is still relatively limited. The concepts presented in this chapter are helpful in understanding BRT design requirements to program traffic lights, be it on simple controllers or as policy delimiters to more complex systems.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 262-267: code points 1-92

Traffic lights eliminate some of the negotiations between vehicles on arrival by determining which movements may proceed at a given moment. Traffic lights may allow conflicting movements, usually not all of them are intense; pedestrians crossing the transversal street are a common one. By reducing negotiations, traffic lights prevent vehicles approaching the intersection from reducing their speeds, raising the time each vehicle spends in the intersection itself (which, by definition, is an area). Traffic signals increase the throughput while keeping intersections safe.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 269-274: code points 1-57

\subsubsection{1}{Phase}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:phase}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 276-282: code points 1-33

One set of movements that is allowed to occur at the same time is called a signal phase. It should be noted that some movements are allowed during several phases; in many countries, allowing curbside turns at all times is the standard. Some may use expressions like “allowing a particular turn in the beginning of phase two” when technically it should be “adding a short phase before phase two where a particular turn will be allowed.”\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 278-282: code points 1-33

\subsubsection{2}{Effective Green Time (T\textsubscript{green})}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:effective-green-time-tgreen}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 284-290: code points 1-6

The phase duration (or length) refers to its “effective green time,” which is the time vehicles are considered effectively moving, which may start a little after the green light is given and end in the middle of yellow lights (where such are used), or in the first moments of red (clearance interval). For this chapter, where queueing and intersection capacity are evaluated, green time means “effective green time.”\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 286-290: code points 1-6

\subsubsection{3}{Cycle Time (T\textsubscript{cycle})}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:cycle-time-tcycle}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 292-297: code points 1-111

Excluding situations where special phases are activated by detectors, the traffic signals in an intersection repeat the order of the phases successively in cycles. The cycle time can be measured as the time between when the green light is given until the next time it is given again (after it has changed to red once). In this chapter, “cycle time” alone refers to a traffic light cycle time (route cycle times are not discussed).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 294-297: code points 1-111

\subsubsection{4}{Red Time (T\textsubscript{red})}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:red-time-tred}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 299-302: code points 1-23

For the interest of intersection capacity and queueing evaluation, red time means cycle time minus (effective) green time.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 301-302: code points 1-23

\subsubsection{5}{Lost Time}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:lost-time}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 304-318: code points 1-91

Lost time is the period between the end of the effective green of a phase and the start of the next. Lost time depends on the signal programming for yellow times and overlapping red (clearance red). It also depends on the enforcement policy and driver behavior (longer lost times are associated with safer intersections), but for the given conditions, there are fixed values.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 306-309: code points 1-69

We refer to lost time as the total lost time per cycle, but lost time can be further split into the start-up and clearance for each phase, each of them being nearly two seconds. One can generally consider that a four-phase signalized intersection has lost a time of sixteen seconds, meaning that the total lost time \emphasis{each cycle} is sixteen seconds.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 311-314: code points 1-42

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/6a2a7929c8c50cbf1ee6007558130f469924208c.png}
		\fignote{7}{For each approach during effective green time, flow starts at saturation until the queue dissolves or the effective green time turns off. And for each approach during red time, there is queue formation, and lost time happens when neither approach has flow.\label{chapter:intersections-and-signal-control:figure:for-each-approach-during-effective-green-time-flow-starts-at-saturation-until-the-queue-dissolves-or-the-effective-green-time-turns-off-and-for-each-approach-during-red-time-there-is-queue-formation-and-lost-time-happens-when-neither-approach-has-flow}}{Elebeta.}
	}
\fi

\subsubsection{6}{Traffic Light Plans}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:traffic-light-plans}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 320-363: code points 1-42

In the same way for intersections in general, the higher the number of turning movements there are in an intersection with traffic lights, the more difficult it is to serve them all. Some movements can happen simultaneously, while some cannot. Reducing the number of phases implies that the number of lanes allowing movements on any phase will be higher, and it also implies that the intersection will have a higher overall throughput (see Section 24.5: Restricting General Traffic Movements).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 322-326: code points 1-84

The optimal phase times in a signalized intersection are such that the cycle time is as brief as possible without growing queues. Having the minimum cycle is optimal because it implies the shortest possible red times, which is similar to the shortest possible waiting times. In order to not have queues, if demand and saturation flow is known for each approach, the minimal number of effective green seconds per hour required can be calculated for an approach that does not form queues. If this is calculated for all approaches, the minimum effective green time for that intersection as a whole is known, and the total number of effective green seconds in an hour shall be way below 3,600, leaving the difference to be designated as lost time.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 328-334: code points 1-104

Contradictory as it seems at first, the best signal programming is such that it has the maximum lost time per hour, because that implies the highest number of cycles per hour. For example, if required green time for vehicles in the intersection is 3,200 seconds, the intersection is close to collapsing. This is because there are only 400 seconds per hour to allow pedestrian crossings and lost time still needs to be added. Assuming there are two vehicle phases plus a minimal pedestrian phase of 6 seconds, and an extra 4 seconds for each phase change, each cycle will need an additional 18 seconds (= 6 + 4 * 3) beyond vehicle green time. This extra time for all cycles during one hour is defined as 400 seconds, so the intersection can have a maximum of 22 complete cycles (= 400 \slash{} 18) or 162 seconds (almost 3 minutes) of cycle time.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 336-344: code points 1-14

Time of day should be taken into consideration because infrastructure that is sized based on the peak use may eventually become underused at other times of the day. Traffic signal timing plans for peak moments could lead to unnecessary delays at other points during the day. Traffic light plans should change throughout the day as demand changes; one extreme example of this is shutting down a signal during late night and early morning hours (or switching to a yellow blinking signal).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 346-350: code points 1-63

Traffic signal programming shall change throughout the day, so that green and red cycle times must change based on different programming for the time of the day (as well as week and season) and, where available, change based on traffic detection applied to parameters in the programming for that moment. When we discuss these features as fixed, we must understand them as the limiting parameters for the traffic controller that allow adaptive changes based on detection.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 352-356: code points 1-58

We look at infrastructure layouts associated with the traffic-signal plan for the peak hours of the day for each flow, and if there is enough capacity during this time frame, then there certainly will be in others, although traffic signal programs need to be different to minimize travel times. To represent the peak, we use and measure the busiest hour of the day for the given flow (as a reminder: we survey data with smaller intervals than one hour, so a given measure of the busiest hour might have happened from 7:15 a.m. to 8:15 a.m., for example).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 358-363: code points 1-42

\subsubsection{7}{Traffic Signal Coordination}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:traffic-signal-coordination}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 365-376: code points 1-80

Coordination is the synchronization of several traffic lights along a path to produce a “green wave” for that route, eliminating waiting while still keeping the required\slash{}projected capacity for all flows. With proper planning, it is possible to coordinate several routes (including pedestrians and to some extent, public transport) in the same area by establishing priorities among them. Eventually, routes with lower priority end up having more breaks in their green waves and some intersections will need to have irregular green times for the transversal flows (still fixed in a larger cycle measure: one long, one short, one long, one short, and so on).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 367-373: code points 1-43

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/cdf6d266177cf13d74fe0e6e5b5c1dee89511565.png}
		\fignote{8}{Traffic light coordination can provide green waves to several routes by synchronizing the opening of green phases with the flow speed. Image\label{chapter:intersections-and-signal-control:figure:traffic-light-coordination-can-provide-green-waves-to-several-routes-by-synchronizing-the-opening-of-green-phases-with-the-flow-speed-image}}{Elebeta.}
	}
\fi

\subsubsection{8}{Detection or Actuation}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:detection-or-actuation}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 378-403: code points 1-20

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/595f87a20569733992fd1bc167644cddf65488da.png}
		\fignote{9}{As an example of actuation, pedestrians may “call the controller for a service” by pressing a button, as in this crossing in São Paulo.\label{chapter:intersections-and-signal-control:figure:as-an-example-of-actuation-pedestrians-may-call-the-controller-for-a-service-by-pressing-a-button-as-in-this-crossing-in-so-paulo}}{Jonas Malaco.}
	}
\fi

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/4c9fed37827b42e4195b02b4117c08bedf7a9d03.jpeg}
		\fignote{10}{To feed São Paulo’s central traffic control, vehicles’ metallic surfaces are detected when approaching an intersection.\label{chapter:intersections-and-signal-control:figure:to-feed-so-paulos-central-traffic-control-vehicles-metallic-surfaces-are-detected-when-approaching-an-intersection}}{Arthur Szász.}
	}
\fi

Actuation is the form in which the user informs his or her presence to a traffic signal controller, for example:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 386-387: code points 1-12

\begin{itemize}
\item A pedestrian pressing a button to request a crossing (Figure 24.9);% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 389-390: code points 1-0
\item A vehicle passing over a magnetic induction loop buried in the traffic lane (Figure 24.10).% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 390-390: code points 1-97
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 389-390: code points 1-97

Actuation can be used in many ways, isolated or in conjunction with traffic control signs:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 392-392: code points 1-90

\begin{itemize}
\item Add a required phase for pedestrians or cross-traffic turns (semi-actuated control);% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 394-395: code points 1-0
\item Determine the length of every phase (full-actuated control);% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 395-396: code points 1-0
\item Activate a preestablished plan that will eventually be coordinated (actuated pre-time control);% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 396-397: code points 1-0
\item Establish public transport priority (see Section 24.3.2: Active Signal Priority);% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 397-398: code points 1-0
\item Input data about movement requests to a central traffic control that computes several inputs at once to select a plan of operation;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 398-400: code points 1-0
\item Input data about movement requests to central controllers that adjust traffic signal parameters by evaluating alternative strategies for the requirements in real time (adaptive control, among which “Split Cycle Offset Optimization Technique” or “SCOOT model” is a common reference for this type of adaptive central controller).% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 400-403: code points 1-20
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 394-403: code points 1-20

\subsubsection{9}{Intersection Capacity}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:intersection-capacity}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 405-415: code points 1-60

Considering the definition of an intersection as the area where vehicles come into conflict, the capacity of the intersection should be measured as the total number of (equivalent) vehicles that cross it, tallying the total of all the movement.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 407-409: code points 1-30

But for the purposes of this chapter, intersection capacity refers to the entrance section (the approach or stop line) of only the road segment being analyzed. Furthermore, we are particularly interested in signalized intersections, assuming that the corridor where the BRT is placed has preference at smaller non-signalized intersections that do not cause other meaningful interference to mixed traffic or to BRT, which is not included in the basic saturation flow measures.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 411-415: code points 1-60

\subsubsection{10}{Relative Green (K\textsubscript{green})}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:relative-green-kgreen}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 417-434: code points 1-20

The proportion of time allowed by a green light for a flow to cross an intersection \emphasis{(Kgreen)} is given by the equation below.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 419-420: code points 1-22

Eq. 24.5\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 422-422: code points 1-8

$ K_\text{green} = {T_\text{green}  \over T_{cycle} }$\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 424-424: code points 1-56

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 426-426: code points 1-6

\begin{itemize}
\item $ K_\text{green} $: Relative green, or the proportion of time given by a green light for a flow to cross an intersection;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 428-429: code points 1-0
\item $ T_\text{green} $: Time given by a green light for a flow to cross an intersection;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 429-430: code points 1-0
\item $ T_\text{cycle} $: Time given by the signal cycle.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 430-430: code points 1-59
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 428-430: code points 1-59

The previous and following equations apply to fixed cycles, but to measure the relative green of a coordinated traffic light with irregular times, one should consider the total green time along a repetition cycle (short, long).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 432-434: code points 1-20

\subsubsection{11}{Relative Red (K\textsubscript{red})}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:relative-red-kred}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 436-470: code points 1-129

The proportion of time that traffic is held by a red light in a given approach \emphasis{(Kred)} is given by the equation below.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 438-439: code points 1-19

Eq. 24.6\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 441-441: code points 1-8

$ K_\text{red} = {T_\text{red}  \over T_{cycle}} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 443-443: code points 1-52

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 445-445: code points 1-6

\begin{itemize}
\item $ K_\text{red} $: Relative red, or the proportion of time that traffic is held by a red light in a given approach;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 447-448: code points 1-0
\item $ T_\text{red} $: Time given by a red light holding traffic from crossing an intersection;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 448-449: code points 1-0
\item $ T_\text{cycle} $: Time given by the signal cycle.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 449-449: code points 1-59
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 447-449: code points 1-59

By the relation of this definition and that of red time, $ T_\text{red} = T_\text{cycle} - T_\text{green} $, we can conclude that $  T_\text{red} + T_\text{green} = T_\text{cycle} \leftrightarrow 
   {T_\text{red}  \over T_{cycle}} + {T_\text{green}  \over T_{cycle} } ={T_\text{cycle}  \over T_{cycle} } \leftrightarrow
    K_\text{red} + K_\text{green} = 1 $ and therefore:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 451-454: code points 1-55

Eq. 24.7\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 456-456: code points 1-8

$ K_\text{red} = 1 - K_\text{green} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 458-458: code points 1-39

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 460-461: code points 1-0

\begin{itemize}
\item $ K_\text{red} $: Relative red, or the proportion of time that traffic is held by a red light in a given approach;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 461-462: code points 1-0
\item $ K_\text{green} $: Relative green, or the proportion of time given by a green light for a flow to cross an intersection.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 462-462: code points 1-129
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 461-462: code points 1-129

Eq. 24.8\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 464-464: code points 1-8

$ K_\text{green} = 1 - K_\text{red} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 466-466: code points 1-39

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 468-469: code points 1-0

\begin{itemize}
\item $ K_\text{red} $: Relative red, or the proportion of time that traffic is held by a red light in a given approach;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 469-470: code points 1-0
\item $ K_\text{green} $: Relative green, or the proportion of time given by a green light for a flow to cross an intersection.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 470-470: code points 1-129
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 469-470: code points 1-129

\subsubsection{12}{Capacity at a Signalized Intersection Approach}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:capacity-at-a-signalized-intersection-approach}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 472-497: code points 1-43

The capacity at a signalized intersection approach is simply the saturation flow of the approach multiplied by the proportion of time it is in operation. Unless stated otherwise, intersection capacity refers to this.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 474-476: code points 1-5

Eq. 24.9\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 478-478: code points 1-8

$ \text{CapFlow}_\text{intersection} = \text{saturationflowperlane} * \text{NLanes} * K_\text{green} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 480-480: code points 1-104

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 482-483: code points 1-0

\begin{itemize}
\item $ \text{CapFlow}_\text{intersection} $: Capacity at a signalized intersection approach;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 483-484: code points 1-0
\item $ \text{saturationflowperlane} $: Maximum flow a given lane can handle;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 484-485: code points 1-0
\item $ \text{NLanes} $: Number of lanes;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 485-486: code points 1-0
\item $ K_\text{green} $: Relative green, or the proportion of time given by a green light for a flow to cross an intersection;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 486-486: code points 1-129
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 483-486: code points 1-129

The capacity away from the intersection can be considered by this definition, if one assumes that $K_\text{green}$ is equal to one—that is, an uninterrupted flow.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 488-488: code points 1-164

Eq. 24.10\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 490-490: code points 1-9

$ \text{CapFlow}_\text{intersection} = \text{saturationflowperlane} *NLanes $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 492-492: code points 1-79

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 494-495: code points 1-0

\begin{itemize}
\item $ \text{CapFlow}_\text{intersection} $:Capacity at a signalized intersection approach;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 495-496: code points 1-0
\item $ \text{saturationflowperlane} $: Maximum flow a given lane can handle;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 496-497: code points 1-0
\item $ \text{NLanes} $: Number of lanes.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 497-497: code points 1-43
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 495-497: code points 1-43

\subsubsection{13}{Demand Saturation Level (X)}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:demand-saturation-level-x}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 499-517: code points 1-97

Demand saturation level is a dimensionless form of expressing demand by comparing it to the maximum that the infrastructure under analysis can serve. Applied to a road section, it is given by demand flow (how many vehicles want to cross the section for the duration of time interval) over the saturation flow. This means that if the section is the entrance to an intersection, the reference is the discharge flow rate (how many vehicles can cross the section if the traffic light is green during the whole interval).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 501-505: code points 1-103

Eq. 24.11\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 507-507: code points 1-9

$ X = {\text{DemandFlow} \over \text{SaturationFlow}} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 509-509: code points 1-57

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 511-512: code points 1-0

\begin{itemize}
\item $ X $: Demand saturation level;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 512-513: code points 1-0
\item $ \text{DemandFlow} $: Number of vehicles that want to use the section for the time interval;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 513-514: code points 1-0
\item $ \text{SaturationFlow} $: Maximum flow the section can handle under prevailing use;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 514-514: code points 1-92
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 512-514: code points 1-92

Demand saturation level is sometimes referred to as “saturation level” or just “saturation,” which can create confusion with “saturation flow.” Also, we use “demand level” and “X” in this chapter.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 516-517: code points 1-97

\subsubsection{14}{Demand to Signal Capacity Level (XSignal)}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:basic-concepts:subSection:traffic-signal-concepts:subSubSection:demand-to-signal-capacity-level-xsignal}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 519-625: code points 1-0

This is a variant form of expressing demand saturation level at the traffic light, and instead of comparing it to the maximum possible throughput, this compares it with the possible throughput under current programming. It is given by demand flow over capacity flow. The reference is the traffic sign effective capacity (how many vehicles can cross the section during the interval that the traffic light is green).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 521-524: code points 1-89

Eq. 24.12\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 526-526: code points 1-9

$ \text{XSignal} = { \text{DemandFlow} \over \text{CapacityFlow}} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 528-528: code points 1-69

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 530-531: code points 1-0

\begin{itemize}
\item $ \text{XSignal} $: Demand to signal capacity level;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 531-532: code points 1-0
\item $ \text{DemandFlow} $: Number of vehicles that want to use the section for the time interval;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 532-533: code points 1-0
\item $ \text{CapacityFlow} $: Maximum flow that can cross the section during the interval that the traffic light is green.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 533-534: code points 1-6
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 531-534: code points 1-6

Eq. 24.13\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 536-536: code points 1-9

$ \text{XSignal} = {  \text{DemandFlow} \over \text{SaturationFlow} * K_\text{green} } $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 538-538: code points 1-90

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 540-541: code points 1-0

\begin{itemize}
\item $ \text{XSignal} $: Demand to signal capacity level;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 541-542: code points 1-0
\item $ \text{DemandFlow} $: Number of vehicles that want to use the section for the time interval;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 542-543: code points 1-0
\item $ \text{SaturationFlow} $: Maximum flow a section can handle under prevailing use;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 543-544: code points 1-0
\item $ K_\text{green} $: Relative green, or the proportion of time given by a green light for a flow to cross an intersection.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 544-544: code points 1-129
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 541-544: code points 1-129

Demand to signal capacity level is particularly relevant for the calculation of traffic sign delay below in the particular formulation we use. Sometimes it is called “signal saturation level” as the following definition is also possible.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 546-548: code points 1-28

Eq. 24.14\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 550-550: code points 1-9

$ \text{XSignal} = {X \over  K_\text{green} } $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 552-552: code points 1-49

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 554-555: code points 1-0

\begin{itemize}
\item $ \text{XSignal} $: Demand to signal capacity level;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 555-556: code points 1-0
\item $ X $: Demand saturation level;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 556-557: code points 1-0
\item $ K_\text{green} $: Relative green, or the proportion of time given by a green light for a flow to cross an intersection.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 557-557: code points 1-129
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 555-557: code points 1-129

\emphasis{Signal Delay ($T_\text{signal}$)}\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 559-559: code points 1-36

The calculation assumes that arrivals are random and departure headways are uniform, which is applicable only for undersaturated conditions and predicts infinite delay when arrival flows approach capacity. This is realistic for design purposes, as we intend to promote undersaturated conditions.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 561-563: code points 1-89

Signal delay is composed of two terms:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 565-566: code points 1-0

\begin{itemize}
\item The first term ($T_\text{queue}$) is the delay due to a uniform rate of vehicle arrivals and departures at the signal;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 566-568: code points 1-0
\item The second term ($ T_\text{random}$) is the random delay term, which accounts for the effect of random arrivals. But if demand of signal capacity level is below 50 percent, then it should be ignored.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 568-569: code points 1-86
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 566-569: code points 1-86

Eq. 24.15\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 571-571: code points 1-9

$ T_\text{signal}=T_\text{queue}+T_\text{random} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 573-573: code points 1-52

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 575-576: code points 1-0

\begin{itemize}
\item $ T_\text{signal} $: Signal delay;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 576-577: code points 1-0
\item $ T_\text{queue} $: Delay due to a uniform rate of vehicle arrivals and departures at the signal;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 577-578: code points 1-0
\item $ T_\text{random} $: Random delay term, which accounts for the effect of random arrivals.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 578-578: code points 1-97
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 576-578: code points 1-97

The first term is deductible as the area below the queueing in Figure 24.7 over the number of vehicles during a cycle ($ \text{DemandFlow} * T_\text{cycle}$).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 580-581: code points 1-57

Eq. 24.16\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 583-583: code points 1-9

$ T_\text{queue}={ T_\text{red}^2 \over 2 * T_\text{cycle} * (1-X)} $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 585-585: code points 1-71

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 587-588: code points 1-0

\begin{itemize}
\item $ T_\text{queue} $: Delay due to a uniform rate of vehicle arrivals and departures at the signal;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 588-589: code points 1-0
\item $ T_\text{red} $: Time given by a red light holding traffic from crossing an intersection;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 589-590: code points 1-0
\item $ T_\text{cycle} $: Time given by the signal cycle.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 590-590: code points 1-59
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 588-590: code points 1-59

The extra delay in queuing, caused by the non-regularity of arrivals in the traffic light ($T_\text{random}$) is a function of the demand-to-signal capacity level ($\text{XSignal}$) and a regularity of vehicles (buses in our case) arrival coefficient ($K_\text{reg}$).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 592-594: code points 1-19

If the signal saturation ($\text{XSignal}$) is low, the randomness of arrivals will not generate extra time in queueing formation. As the signal saturation increases, the impact on extra time due to the expected randomness of arrivals becomes bigger than the increments. If the signal saturation is bigger than one (there are more vehicles willing to use the lane than what the traffic light can handle), there will be severe busway congestion (congestion would happen even if there were no random arrivals at all). So, the extra queueing delay due to randomness is calculated by:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 596-601: code points 1-60

Eq. 24.17\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 603-603: code points 1-9

If $ \text{Xsignal} < K_\text{reg} $, then $ T_\text{random} = 0 $\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 605-605: code points 1-70

If $K_\text{reg} \leq \text{Xsignal} < 1$, then: $ T_\text{random} = {{\text{XSignal} - K_\text{reg}  \over 1 - \text{XSignal} } * 1 \over \text{SaturationFlow}} $;\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 607-607: code points 1-168

If $ \text{Xsignal} \geq 1 $, then there would be severe congestion ($T_\text{random} \to \infty $).\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 609-609: code points 1-104

Where:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 611-612: code points 1-0

\begin{itemize}
\item $ \text{XSignal} $: Demand to signal capacity level;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 612-613: code points 1-0
\item $ \text{Trandom} $: Random delay term, which accounts for the effect of random arrivals.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 613-614: code points 1-0
\item $ \text{SaturationFlow} $: Maximum flow a section can handle under prevailing use;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 614-615: code points 1-0
\item {$ K_\text{reg} $: Regularity factor; it is a number related to the chance a bus has to arrive within the signal cycle as detailed below:\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 615-617: code points 8-4

\begin{itemize}
\item It would equal one if there were total regularity in vehicle arrivals;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 617-618: code points 5-4
\item It would be 0.5 if half of the vehicles arrive more than one signal cycle later than when they are expected;% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 618-620: code points 5-4
\item The value used to represent uncertain arrivals is 0.5.% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 620-620: code points 5-64
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 617-620: code points 5-64

}
\end{itemize}
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 612-620: code points 1-65

This formula is a variation of the model proposed by Webster in 1958, slightly simpler than originally proposed but with a smoother transition when the random delay becomes more relevant than the practical modification most commonly applied.\par
% @ guide/24-intersections_and_signal_control/241-basic-concepts.src: lines 622-625: code points 1-0

\section{2}{Approach to Intersection Design}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:approach-to-intersection-design}
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 1-311: code points 1-45

\quotation{Idiopathic, from the Latin meaning we’re idiots cause we can’t figure out what’s causing it.}{Gregory House, MD (as played by actor Hugh Laurie), “Role Model,” House, 2005}
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 3-4: code points 1-79

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/c646a89a5ddcae1a6d8bff6a374595926a978a08.jpeg}
		\fignote{11}{The introduction of BRT and better design changes poorly controlled and congested intersections, often leading to efficiency improvements for both public transport vehicles and mixed traffic.\label{chapter:intersections-and-signal-control:figure:the-introduction-of-brt-and-better-design-changes-poorly-controlled-and-congested-intersections-often-leading-to-efficiency-improvements-for-both-public-transport-vehicles-and-mixed-traffic}}{Lloyd Wright.}
	}
\fi

BRT systems are generally built on corridors where mixed-traffic congestion is already a problem, or where congestion is likely to occur in the near future; otherwise there would be no benefit in building a segregated busway. The worse the congestion appears, the greater the benefit of the exclusive busway (Figure 24.11). If a BRT system makes public transport services better but mixed traffic worse, it will be less politically successful than if it makes public transport better and also improves mixed-traffic flow. BRT system planners therefore generally try to minimize adverse impacts on mixed traffic.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 10-15: code points 1-95

Intersections are critical to stations, as they represent an important point along any BRT corridor. A poorly designed intersection or a poorly timed signal phase can substantially reduce system capacity and speed, especially by hindering access to stations. Finding solutions to optimize intersection performance can do much to improve system efficiency. Generally, the three main objectives of intersection design along a BRT corridor are:\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 17-21: code points 1-25

\begin{enumerate}
\item To provide safe and convenient crossings for pedestrians;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 23-24: code points 1-0
\item To minimize delay for BRT vehicles;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 24-25: code points 1-0
\item To minimize delay for mixed traffic.% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 25-25: code points 1-44
\end{enumerate}
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 23-25: code points 1-44

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/563c4fd8266f2fb5e0204637459132860f72ef24.jpeg}
		\fignote{12}{Intersection design affects the BRT system’s efficiency, pedestrian safety, and the access and flows of mixed-traffic vehicles.\label{chapter:intersections-and-signal-control:figure:intersection-design-affects-the-brt-systems-efficiency-pedestrian-safety-and-the-access-and-flows-of-mixed-traffic-vehicles}}{Lloyd Wright.}
	}
\fi

Travel times for walking trips are improved by following these objectives, but it should be noted that pedestrians’ safety and accessibility have the highest priority. Some methods take into account pedestrian times in order to analyze alternatives, and the approach discussed here does not equalize pedestrians by inputting delays into the process. Current procedures mostly try to fit demand needs into the available space so that pedestrians can make all crossings safely; bus lane queues are not so long that they block stations; and desired car movements are still possible, all without worsening congestion. Keep in mind that if public and private transport users’ times were equalized, every street with one vehicle carrying fifty passengers every two minutes would have an exclusive bus lane.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 30-37: code points 1-68

It is generally not advisable to use a standard intersection configuration throughout a BRT corridor. Rather, it is best to design the intersection for the specific conditions at the given location. The impact of a planned BRT system on overall intersection performance is often a significant consideration when deciding on a service plan for the BRT system, the location of the stations, and the design of the stations.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 39-43: code points 1-9

BRT system planners have used the following tools to rationalize intersections:\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 45-45: code points 1-79

\begin{itemize}
\item Simplify the BRT system’s routing structure to optimize turning movements into the corridor;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 47-48: code points 1-0
\item Optimize the number of intersections along the corridor;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 48-49: code points 1-0
\item Restrict as many mixed-traffic turning movements on the BRT corridors as possible;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 49-50: code points 1-0
\item Optimize the location of the station relative to adjacent intersections;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 50-51: code points 1-0
\item Optimize the signal phasing and consider signal priority for public transport vehicles.% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 51-51: code points 1-93
\end{itemize}
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 47-51: code points 1-93

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/5ba68a627d682e5e2701c59bd37deb7067c13bac.jpeg}
		\fignote{13}{A typical major intersection on a BRT corridor in Guangzhou, China. Note that the station of the BRT corridor is located away from the intersection with Chibei Avenue, and in order to turn across traffic, the two-phase intersection requires a U-turn in the perpendicular road. Before the BRT, this four-phase intersection was a major traffic-congestion point. Image\label{chapter:intersections-and-signal-control:figure:a-typical-major-intersection-on-a-brt-corridor-in-guangzhou-china-note-that-the-station-of-the-brt-corridor-is-located-away-from-the-intersection-with-chibei-avenue-and-in-order-to-turn-across-traffic-the-two-phase-intersection-requires-a-u-turn-in-the-perpendicular-road-before-the-brt-this-four-phase-intersection-was-a-major-traffic-congestion-point-image}}{Karl Fjellstrom, ITDP.}
	}
\fi

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/ec52daf33ef3156ba939772f6f1b21f7560dc74c.jpeg}
		\fignote{14}{The same intersection as depicted in Figure 24.13 on a BRT corridor in Guangzhou, China. The station is located away from the intersection of the BRT corridor and Chibei Avenue. In order to turn across traffic, the two-phase intersection requires a U-turn in the perpendicular road. Before the BRT, this four-phase intersection was a major traffic-congestion point.\label{chapter:intersections-and-signal-control:figure:the-same-intersection-as-depicted-in-figure-2413-on-a-brt-corridor-in-guangzhou-china-the-station-is-located-away-from-the-intersection-of-the-brt-corridor-and-chibei-avenue-in-order-to-turn-across-traffic-the-two-phase-intersection-requires-a-u-turn-in-the-perpendicular-road-before-the-brt-this-four-phase-intersection-was-a-major-traffic-congestion-point}}{ITDP and GMEDRI.}
	}
\fi

Every decision and solution proposed during the intersection design process should be technically supported by the elaboration of a comprehensive traffic study, where directional flow counts for cars and pedestrians are categorized and carried out at every active intersection (signalized or not) along the corridor being designed. This is necessary to diagnose the current performance of each intersection and forecast a future scenario incorporating the operational changes a BRT corridor might bring.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 64-68: code points 1-74

\subsection{1}{Corridor Audits}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:approach-to-intersection-design:subSection:corridor-audits}
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 70-101: code points 1-100

As a first step to intersection design, BRT system planners should carefully review the existing mixed-traffic bottlenecks in the corridor. A small number of bottlenecks are often responsible for the vast majority of mixed-traffic delay. These bottlenecks are usually due to one or more of the following conditions:\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 72-74: code points 1-101

\begin{itemize}
\item Narrow bridges and tunnels;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 76-77: code points 1-0
\item Traffic convergence points;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 77-78: code points 1-0
\item Poorly regulated\slash{}enforced parking;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 78-79: code points 1-0
\item Suboptimal timing at traffic signals;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 79-80: code points 1-0
\item Improperly designed and channeled intersections;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 80-81: code points 1-0
\item Badly placed bus stops or unregulated stopping of public transport vehicles.% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 81-81: code points 1-82
\end{itemize}
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 76-81: code points 1-82

Quite often a new BRT system can lead to a reduction of the number of lanes available to mixed traffic. While ideally the removal of a large number of buses from the mixed-traffic lanes will avoid worsening congestion in the mixed-traffic lanes, this is not always possible, and the mixed-traffic saturation level may increase.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 83-86: code points 1-19

Figure 24.15 illustrates the vehicular demand saturation level along a planned BRT corridor and what could be expected if one lane is removed.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 88-89: code points 1-41

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/41982d7fe3c7f9c506c68e08540b85508570ee7c.png}
		\fignote{15}{Current demand saturation level for mixed traffic can be expected to off-set the transference of one lane to the planned BRT system.\label{chapter:intersections-and-signal-control:figure:current-demand-saturation-level-for-mixed-traffic-can-be-expected-to-off-set-the-transference-of-one-lane-to-the-planned-brt-system}}{ITDP.}
	}
\fi

The most serious bottlenecks—points A, B, and E—are signalized intersections. Point C might be a bridge or tunnel where, for example, lanes are reduced from three to two, increasing saturation by 50 percent. Point D might be a popular destination such as a shopping mall where an extra volume of vehicles enters the road, increasing saturation. It might also be a popular bus interchange, a street market, or an area with regulated on-street parking.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 94-98: code points 1-33

If no measures are taken to mitigate the lane removal due to the BRT implementation, then congestion restricted to point B will occur at A, B, C, and E. These points now require more careful attention.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 100-101: code points 1-100

\subsection{2}{Solution Approach}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:approach-to-intersection-design:subSection:solution-approach}
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 103-123: code points 1-18

Once the basic routing structure of the new BRT system has been determined, system designers should have a reasonable idea about likely vehicle frequencies within the system.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 105-106: code points 1-74

Considering the placement of the BRT corridor and its requirements, the non-intersection bottlenecks should be addressed first. These problem points can generally be resolved through a combination of tightening parking regulation and enforcement, strengthening vendor regulation and enforcement, narrowing medians, improving parallel roads, or widening roads if all else fails.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 108-111: code points 1-62

The second analysis should determine if the busway will congest given the current intersection signal phasing and lane allocation along the BRT corridor. Each intersection in the corridor should be analyzed. An example of the intersection delay impacts calculation is given in the next section. Intersections that do not match the BRT requirements should be redesigned.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 113-116: code points 1-60

Once the implementation of the new BRT system requires changing the intersection design anyway, the opportunity should be taken to improve the overall efficiency of the intersection. Packaging these intersection improvements with the introduction of the new BRT system will help improve public acceptance of the new BRT system. The less efficient the intersection was before the BRT system, the greater the potential there will be to design the new system in a way that improves conditions for both public transport passengers and mixed traffic.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 118-123: code points 1-18

\subsection{3}{Signal Delay on BRT}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:approach-to-intersection-design:subSection:signal-delay-on-brt}
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 125-311: code points 1-45

Table 24.2 shows an example of the variation in the average traffic signal delay for each BRT vehicle crossing an intersection as a function of the red and green signal duration within a defined cycle time.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 127-128: code points 1-104

Signal delay is given by Equation 24.15 and fixed parameters for the example are:\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 130-131: code points 1-0

\begin{itemize}
\item Cycle time: Tcycle = 80 seconds;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 131-132: code points 1-0
\item BRT vehicle frequency across the intersection: DemandFlow = 200 articulated-bus\slash{}hour;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 132-133: code points 1-0
\item BRT lanes: NLanes = 1 lane;% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 133-134: code points 1-0
\item Discharge flow rate: saturationflowperlane = 720 articulated-bus\slash{}hour\slash{}lane.% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 134-135: code points 1-0
\end{itemize}
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 131-135: code points 1-0

\tabletitle{2}{- Signal delay as function of red light}
\label{chapter:intersections-and-signal-control:table:--signal-delay-as-function-of-red-light}
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	\color{gray75}\bfseries Red light time (seconds)& \color{gray75}\bfseries Green light time (seconds)& \color{gray75}\bfseries Average signal delay (TF) (seconds)& \color{gray75}\bfseries Random queuing delay (TQs) (seconds)& \color{gray75}\bfseries Total signal delay (TS) (seconds)& \color{gray75}\bfseries Demand to signal capacity level (XSignal) \cr
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% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 135-297: code points 1-9

Thus, if there are 200 articulated buses per hour in a single lane, and there is an 80-second traffic signal cycle with a red phase of 35 seconds, then there is no difference between total signal delay and average signal delay. In this case there is no additional delay resulting from the randomness of vehicle queues at the stoplight. However, if there is more than 35 seconds of red time, the random queuing of buses at the traffic light begins to add additional delay.\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 299-303: code points 1-58

In summary, intersection delay is largely a function of red time as a share of total signal time. If demand-to-signal capacity level is greater than 0.65, random delay becomes significant, and the project design should be changed to give a higher proportion of green time, and\slash{}or a second BRT lane on the approach to the intersection should be considered (Figure 24.16).\par
% @ guide/24-intersections_and_signal_control/approach-to-intersection-design.src: lines 305-308: code points 1-56

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/c97b9eeabd15f29308c10280618175309be145e1.jpeg}
		\fignote{16}{Single to double lanes just before the intersection in Bogotá to ensure proper capacity.\label{chapter:intersections-and-signal-control:figure:single-to-double-lanes-just-before-the-intersection-in-bogot-to-ensure-proper-capacity}}{Oscar Edmundo Diaz, GSD+.}
	}
\fi

\section{3}{Traffic Signal Priority}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:traffic-signal-priority}
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 1-95: code points 1-82

\quotation{On a traffic light green means go and yellow means yield, but on a banana it’s just the opposite. Green means hold on, yellow means go ahead, and red means where the hell did you get that banana.}{Mitch Hedberg, comedian, 1968–2005}
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 3-4: code points 1-36

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/3e88a7225eb01d377a3d0da9313de87b0e43b369.jpeg}
		\fignote{17}{Active signal priority for BRT and restricted turning movements for vehicles in mixed traffic can do much to improve public transport travel times.\label{chapter:intersections-and-signal-control:figure:active-signal-priority-for-brt-and-restricted-turning-movements-for-vehicles-in-mixed-traffic-can-do-much-to-improve-public-transport-travel-times}}{Lloyd Wright.}
	}
\fi

Signal priority for BRT vehicles is the adjustment of traffic signals to give priority to a corridor with a BRT system over a corridor without one, and to give priority to the BRT system over mixed traffic within the same corridor. Once equipment and techniques were developed to do this in a responsive way after the detection of BRT vehicles approaching an intersection, the expression “active signal priority” became the way to indicate this advance. Since then “passive signal priority” is used to indicate that such detection technology is not being applied.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 9-14: code points 1-47

\subsection{1}{Passive Signal Priority}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:traffic-signal-priority:subSection:passive-signal-priority}
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 16-47: code points 1-53

Together with signal phase simplification, passive signal priority is crucial to proper BRT intersection design. The two techniques are complementary and must be considered jointly for implementation.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 18-19: code points 1-95

Prioritization is primarily achieved by extending the relative green time for the BRT corridor over the crossing streets that do not have public transport. This action reduces the travel time of the entire traffic stream (both BRT and mixed-traffic) on the corridor at the expense of the travel time of the crossing traffic stream.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 21-24: code points 1-24

Without special consideration for BRT, the optimal phase time in a signalized intersection is such that the cycle time is as brief as possible without growing queues. At the highest extreme, this guideline would change to give as much green time as possible to the BRT corridor without resulting queues. The longest green signal phase would depend on the flow of mixed traffic on the crossing street. The ideal way to balance the traffic light, however, is to consider the average wait time by each flow, including pedestrians multiplied by the number of people in each flow.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 26-31: code points 1-60

In applying traffic signal priority to a BRT corridor, it is typical that cycle time becomes as low as 60 seconds and does not rise above 120 seconds except at major intersections or during peak hours in order to allow larger relative green time for the BRT corridor. The relative green time faced by the BRT system should be extended above 50 percent, if possible. It is typical for the BRT green time to be 30 seconds in a 60-second cycle or 40 to 60 seconds in a 120-second cycle.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 33-37: code points 1-77

Synchronization of green signal phases between intersections (or “green wave,” see coordination as discussed in Section 24.1.3: Traffic Signal Concepts) is not common with BRT systems because BRT travel times are not regularly subject to variable dwell time at stations (especially when multiple route services use the same corridor or frequencies are high). If BRT vehicle speeds are reasonably predictable or controlled, then it is possible to coordinate traffic lights in a BRT corridor. This practice is used in Ottawa, Ontario, Canada (Levinson et al., 2003b). If boarding and alighting times are somewhat regular and of the same magnitude of the green time of the green wave planned for mixed traffic, coordination will lead to the opposite effect, as every time the BRT vehicles dwell in a station they are likely to reach the next traffic light at the beginning of the red light.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 39-47: code points 1-53

\subsection{2}{Active Signal Priority}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:traffic-signal-priority:subSection:active-signal-priority}
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 49-95: code points 1-82

Active, or real-time priority techniques, change the actual traffic signal phasing when a BRT vehicle is observed to be approaching the intersection.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 51-52: code points 1-47

The normal vehicle identification mechanism is to have a transponder detect the BRT vehicle prior to its arrival at the stop line. If the BRT vehicle is detected during the green phase, and the green phase is nearing the yellow phase, then the green phase is extended. If the detection occurs during the red or the yellow interval, the green time is recalled more quickly than normal. Some general guidelines for applying phase extension or phase shortening include:\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 54-59: code points 1-0

\begin{itemize}
\item The minimum side street green time is set based on the amount of time pedestrians need to cross the road;% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 59-61: code points 1-0
\item The amount of green signal extension or advance should be up to a specific, set maximum;% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 61-62: code points 1-0
\item The BRT corridor green is not generally both advanced and extended in the same cycle.% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 62-62: code points 1-91
\end{itemize}
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 59-62: code points 1-91

The green times are likely to be most easily extended at intersections with light cross traffic.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 64-64: code points 1-96

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/b9bc0aebc8a81c23c458c1138a86217d007dec1e.png}
		\fignote{18}{Active priority can reduce red time for the BRT corridor when the BRT vehicle is detected approaching the intersection.\label{chapter:intersections-and-signal-control:figure:active-priority-can-reduce-red-time-for-the-brt-corridor-when-the-brt-vehicle-is-detected-approaching-the-intersection}}{ITDP}
	}
\fi

\ifxetex
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		\img{\hsize}{infrastructure/assets/c32e0d85b0ae534dc8ff47158e8fc9216aec555d.png}
		\fignote{19}{Using active priority, the green time for the BRT corridor is extended when a BRT vehicle is detected approaching the intersection.\label{chapter:intersections-and-signal-control:figure:using-active-priority-the-green-time-for-the-brt-corridor-is-extended-when-a-brt-vehicle-is-detected-approaching-the-intersection}}{ITDP}
	}
\fi

The importance of active traffic signal priority on BRT vehicle speeds tends to be greatest in systems with fairly low bus volumes, particularly with bus headways longer than five minutes where intersections are frequent and might be a relevant measure for increasing system speeds. In such instances, signal priority may reduce signal delay by between 10 and 20 percent. In this context, it is often easier to give buses signal priority at intersections without major disruption to mixed-traffic flows.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 72-76: code points 1-92

When BRT vehicle headways are less than 2.5 minutes, it is generally difficult to implement active signal priority at all: the non-BRT traffic direction would essentially be in a state of a permanent red phase. However, even with BRT vehicles at high frequencies, giving active priority to the BRT running on less important cross streets can yield benefits of between 4 to 10 percent of the delay in traffic signals. While this savings is not as significant as some other priority measures such as restricting mixed-traffic turns, it can be a justifiable expenditure contributing to efficiency gains as vehicle detection, signaling equipment, and priority software become more common, and their costs increasingly affordable.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 78-85: code points 1-11

At an even higher level of sophistication, the priority phasing can be based on observed traffic levels for both the BRT vehicles and the general traffic. A special weighting can be given to BRT vehicles or to the BRT corridor. In traffic systems where flows are quite irregular, real-time control that adjusts signal times to observed traffic levels can yield benefits. In such real-time systems, phase changing is usually based on a trade-off between the benefits and costs faced by the green and red approaches and for the general principle of shortening red times; a fully actuated system based on total vehicle movements, which also includes BRT vehicles, is probably more important than BRT-specific detection. The application of signal priority, both passive and active, is looked at further in Section 24.7: Merging with Mixed Traffic in Narrow Sections and Section 24.8: BRT Lanes at Roundabouts.\par
% @ guide/24-intersections_and_signal_control/traffic-signal-priority.src: lines 87-95: code points 1-82

\section{4}{Station Location Relative to the Intersection}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:station-location-relative-to-the-intersection}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 1-403: code points 1-0

\quotation{The engineer’s first problem in any design situation is to discover what the problem really is.}{Anonymous}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 3-4: code points 1-11

Intersection and station design should minimize the added travel time of all customers. The station location in relation to the intersection will affect the BRT system’s flow, speed, and required right-of-way. Pedestrian travel times, which seem to be the more obvious reason for determining a station’s location, are far less relevant than they first appear.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 6-9: code points 1-45

Because conditions vary from intersection to intersection, it is generally advisable to find an optimal solution for each intersection rather than to presume that a single solution will always be optimal. The greater the amount of information the planning team has available regarding demand, the easier it will be to evaluate alternatives and find an optimal solution under the existing restrictions.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 11-14: code points 1-94

\subsection{1}{Station Location Possibilities}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:station-location-relative-to-the-intersection:subSection:station-location-possibilities}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 16-88: code points 1-24

The following station locations are possible:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 18-19: code points 1-0

\begin{itemize}
\item {At the intersection:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 19-20: code points 8-0

\begin{itemize}
\item For side-aligned stations, the station can be either nearside or far side—that is, before or after the intersection in each direction;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 20-22: code points 1-0
\item For median stations, if not split, the station will be nearside in one direction and far side in the other;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 22-23: code points 1-13
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 20-23: code points 1-13

}
\item {Away from the intersection;\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 24-25: code points 8-0

\begin{itemize}
\item Near the intersection;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 25-26: code points 1-0
\item Far from the intersection (or mid-block);% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 26-26: code points 1-47
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 25-26: code points 1-47

}
\item Under or over the intersection.% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 27-27: code points 1-39
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 19-27: code points 1-39

\subsubsection{1}{At Intersections}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:station-location-relative-to-the-intersection:subSection:station-location-possibilities:subSubSection:at-intersections}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 29-51: code points 1-63

The normal justification for putting the bus stop at the intersection is that it reduces walking times for customers with destinations or transferring on the crossing street. Unless the red time is really short (fewer than twenty seconds) and station saturation (discussed in Chapter 7: Capacity and Speed) is really low, the resulting saturation of the combination of the intersection plus station (i.e., the proportion of time a BRT vehicle will occupy the area with two functions: queue-box waiting for green light and boarding area) is likely to be greater than one, and this will lead to congestion that will end only after the peak (Figure 24.20). Such a situation clearly will not be compensated for by reducing customer walking times. It also will not be of help to customers that are alighting at that station or must only cross that intersection.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 31-39: code points 1-34

Additionally, such justification is often based on presumptions and rarely on data; only micro-level destination maps based on surveys can effectively quantify walking time benefits of station location relative to the intersection. Furthermore, the large number of transferring customers should be prevented when route service planning is designed.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 41-44: code points 1-40

In the rare case that the station must be located at the intersection, there is an emerging consensus that locating the station before the intersection is preferable, particularly in split platform configurations if the BRT lane is near the median.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 46-48: code points 1-35

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/362128698b93d44464985d01c1d0cd1beaf3f43e.jpeg}
		\fignote{20}{Buses waiting for a traffic light after boarding and alighting is completed in São Paulo; today this station is moved back.\label{chapter:intersections-and-signal-control:figure:buses-waiting-for-a-traffic-light-after-boarding-and-alighting-is-completed-in-so-paulo-today-this-station-is-moved-back}}{Arthur Szász.}
	}
\fi

\subsubsection{2}{Away from the Intersection}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:station-location-relative-to-the-intersection:subSection:station-location-possibilities:subSubSection:away-from-the-intersection}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 53-83: code points 1-39

Stations should in general be around a hundred meters from intersections. As highlighted above and as discussed in the remainder of this section, there should be some space between the intersection and the station since it:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 55-58: code points 1-0

\begin{itemize}
\item Provides the possibility of taking away mixed-traffic space without changing road capacity for the section;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 58-60: code points 1-0
\item Prevents bus queues at the intersection from hindering the station;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 60-61: code points 1-0
\item Leaves width at the intersection for increasing mixed-traffic capacity and turns (Figure 24.21).% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 61-61: code points 1-102
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 58-61: code points 1-102

\ifxetex
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\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/0339cd2de42828afbb6e493cfe5b34b08486c4f5.jpeg}
		\fignote{21}{Double to single BRT lane transition before intersection in Guangzhou, China.\label{chapter:intersections-and-signal-control:figure:double-to-single-brt-lane-transition-before-intersection-in-guangzhou-china}}{Karl Fjellstrom, ITDP.}
	}
\fi

We further divide the description of the station’s location into “near it” or “far from it” (or "mid-block") with regard to the intersection. The aspect to be taken into consideration here is customer access to the station.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 66-68: code points 1-12

Mid-block stations will require access infrastructure not shared nor closely related to the intersection’s pedestrian crossings. In the typical environment discussed here, that is, a station located between mixed-traffic signalized intersections, signalized at-grade options are the likely ideal solutions. But such a solution introduces a new intersection (considering the multimodal definition of it) that needs to be taken into account when evaluating capacity of both the station and mixed-traffic.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 70-74: code points 1-71

We should remember that a crossing for access will be required for curbside mid-block stations as well. Mid-block stations are arguably safer to access than near-intersection stations and cycle times can be shorter. Saturation correction must be applied (see Section 24.4.6: Correction Factor for Station Saturation at Traffic Light).\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 76-79: code points 1-18

\ifxetex
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	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/f88da701c8064992035cbddd103be720c57d0afc.png}
		\fignote{22}{In this proposed road layout for Delhi, the mid-block BRT stations are given additional right-of-way and several access points. At the intersections, right-of-way for vehicles in mixed traffic is maximized.\label{chapter:intersections-and-signal-control:figure:in-this-proposed-road-layout-for-delhi-the-mid-block-brt-stations-are-given-additional-right-of-way-and-several-access-points-at-the-intersections-right-of-way-for-vehicles-in-mixed-traffic-is-maximized}}{ITDP.}
	}
\fi

\subsubsection{3}{Above or Below the Intersection}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:station-location-relative-to-the-intersection:subSection:station-location-possibilities:subSubSection:above-or-below-the-intersection}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 85-88: code points 1-24

This alternative is discussed in Section 24.10: Grade Separation, where other aspects of grade-separated solutions are presented.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 87-88: code points 1-24

\subsection{2}{Minimizing the Number of Mixed-Traffic Lanes Away from the Intersection}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:station-location-relative-to-the-intersection:subSection:minimizing-the-number-of-mixed-traffic-lanes-away-from-the-intersection}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 90-150: code points 1-76

\ifxetex
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\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/6a8854aeaa97d7828e9b30cf18490415b5d27246.jpeg}
		\fignote{23}{A mid-block station location in Seoul allows greater right-of-way width for the station area.\label{chapter:intersections-and-signal-control:figure:a-mid-block-station-location-in-seoul-allows-greater-right-of-way-width-for-the-station-area}}{City of Seoul.}
	}
\fi

Usually the mixed-traffic bottleneck is the intersection, where capacity is 50 to 30 percent (proportional to the green fraction of each approach) of mid-block capacity. So if BRT stations are far from intersections, the general-traffic road capacity can be reduced in its surroundings without any significant impact on the capacity and performance on the segment as a whole. This means that mixed-traffic lanes can be removed, and the space given to the BRT station, thus enabling the widening required for BRT at stations to accommodate passing lanes, and hence provide high capacity at stations without impacting mixed-traffic capacity at all (Figure 24.23).\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 95-101: code points 1-19

For example, at the bus stop, if bus frequencies are high and an overtaking lane is needed at each station, the extra width required will be around 12 meters. If the station is located at the intersection, these 12 meters will be difficult to supply while also providing 6-meter turn lanes for mixed traffic. Separating these functions will allow the same right-of-way to be used for the bus station at mid-block, and for left and right turn signals at the intersection. Figure 24.22 shows an application of this concept within a proposal for the Delhi BRT system.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 103-108: code points 1-43

Capacity in a given control section (CapFlow) is expressed in the equation below.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 110-110: code points 1-81

Eq. 24.18\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 112-112: code points 1-9

$ \text{CapFlow}_\text{intersection} = \text{saturationflowperlane} * \text{Nlanes} * K_\text{green} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 114-114: code points 1-104

Where:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 116-117: code points 1-0

\begin{itemize}
\item $ \text{CapFlow}_\text{intersection} $: Capacity of the evaluated section of control, usually in pcu\slash{}hour;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 117-118: code points 1-0
\item $ \text{saturationflowperlane} $: Saturation flow of one lane (in “ideal conditions,” around 1,800 in urban areas pcu\slash{}hour);% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 118-120: code points 1-0
\item $ N_\text{lanes} $: Total number of available lanes;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 120-121: code points 1-0
\item $ K_\text{green} $: Relative (effective) green time, which is given by Equation 24.5:% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 121-121: code points 1-93
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 117-121: code points 1-93

$ K_\text{green} = { T_\text{green} \over _\text{Tcycle} }$\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 123-123: code points 1-61

Where:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 125-126: code points 1-0

\begin{itemize}
\item $ K_\text{green} $: Relative green, or the proportion of time given by a green light for a flow to cross an intersection;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 126-127: code points 1-0
\item $ T_\text{green} $: Time given by a green light for a flow to cross an intersection;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 127-128: code points 1-0
\item $ T_\text{cycle} $: Time given by the signal cycle.% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 128-128: code points 1-59
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 126-128: code points 1-59

One can evaluate the possibility of narrowing the mixed-traffic road away from the intersection without affecting the capacity of the segment by assuring that capacity away from the intersection (where relative green time can be considered 1 or 100 percent) is greater than capacity in the intersection.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 130-132: code points 1-92

$ \text{FlowCap}_\text{away} \geq \text{FlowCap}_\text{intersection} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 134-134: code points 1-72

$ \text{saturationflowperlane} * \text{NLanes}_\text{away} * K_\text{green away} \geq \text{saturationflowperlane} * \text{NLanes}_\text{intersection} * K_\text{green intersection} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 136-136: code points 1-184

$ \text{NLanes}_\text{away} * K_\text{green away} \geq \text{NLanes}_\text{intersection} * K_\text{green intersection} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 138-138: code points 1-122

$ \text{NLanesaway} \geq \text{NLanes}_\text{intersection} * {K_\text{green intersection} \over K_\text{green away}} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 140-140: code points 1-120

Examples:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 142-143: code points 1-0

\begin{itemize}
\item If near-intersection mixed traffic has 3 lanes ($\text{NLanes}_\text{away} = 3$), and relative green time is 60 percent ($ T_\text{green} \over T_\text{cycle} = 0.6 $), then far from intersection ($\text{Nlanes}_\text{away}$) can be 2 lanes without affecting the segment performance:$ \text{NLanes}_\text{away} \geq  3 * 0.6 = 1.8 $ ;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 143-147: code points 1-0
\item If near-intersection mixed traffic has 2 lanes ($\text{NLanes}_\text{away} = 2$), and relative green time is 50 percent ($ T_\text{green} \over T_\text{cycle} = 0.5 $), then far from intersection ($\text{Nlanes}_\text{away}$) can be only one lane without affecting the segment performance: $ \text{NLanes}_\text{away} \geq  2 * 0.5 = 1.0 $ ;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 147-149: code points 1-0
\item If we are planning a mid-block station with signalized pedestrian crossing for the first example, we would have to keep relative green for traffic mid-block above 90 percent.% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 149-150: code points 1-76
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 143-150: code points 1-76

\subsection{3}{Minimizing the Recommended Distance between the BRT Station and the Intersection from a Mixed Traffic Perspective}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:station-location-relative-to-the-intersection:subSection:minimizing-the-recommended-distance-between-the-brt-station-and-the-intersection-from-a-mixed-traffic-perspective}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 152-207: code points 1-49

NOTE: THIS DISTANCE IS FOR STATIONS THAT TAKE AWAY MIXED-TRAFFIC LANES, NARROWING THE AVAILABLE SPACE FOR CARS AWAY FROM THE INTERSECTION AND ENSURING THAT MIXED-TRAFFIC CAPACITY IS NOT AFFECTED!\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 154-155: code points 1-93

Away from the signalized intersection means far enough to guarantee that the capacity flow in the intersection can last the entire green phase. This is equivalent to ensuring that the queueing space with the same number of lanes of the intersection approach has enough capacity to hold all vehicles that can cross the intersection in the duration of the green phase.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 157-160: code points 1-52

This means the distance from the intersection (Diststation-intersection) has to be greater than the space for queueing vehicles times the number of vehicles that will cross the retention line in one lane.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 162-163: code points 1-104

Considering a saturation flow per lane (saturationflowperlane) of 1,800 pcu\slash{}hour is equivalent to one vehicle every two seconds (passing across the intersection in one lane) and the distance between (the front of) two vehicles (lengthpcu) is 5 meters, this implies that for each second of the green phase the queue will be 2.5 meters short.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 165-168: code points 1-35

$\text{Queue discharge rate} = {\text{flow}_\text{saturation} \over \text{length}_\text{pcu}} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 170-170: code points 1-97

Another way to think about this is that the “speed of the shock wave” starting at the retention line after the traffic signal opens is 2.5 meters per second. That is, the second car behind (5 meters behind) will start to move 2 seconds after the first, the third car behind (10 meters from the retention line) will move after 4 seconds and so on.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 172-175: code points 1-36

$\text{Velocity}_\text{discharge shockwave} = {\text{flow}_\text{saturation} \over \text{length}_\text{pcu}} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 177-177: code points 1-112

Therefore the distance between station and intersection (Diststation-intersection) has to be equal to or greater than the distance that the shock wave can move during the duration of the green phase (Tgreen). Representing the speed of shock wave by Velshock-wave, this can be expressed as:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 179-181: code points 1-80

$ \text{Dist}_\text{station intersection} \geq V_\text{shock wave} *T_\text{green}$\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 183-183: code points 1-85

Using meters and seconds for the measures we have:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 185-185: code points 1-50

Eq. 24.19\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 187-187: code points 1-9

$ \text{Dist}_\text{station intersection} [\text{in meters}] \geq 2.5 * T_\text{green} [\text{in seconds}] $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 189-189: code points 1-110

Where:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 191-192: code points 1-0

\begin{itemize}
\item $ \text{Dist}_\text{station-intersection} $:Distance between station and intersection;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 192-193: code points 1-0
\item $ T_\text{green} $: Time given by a green light for a flow to cross an intersection.% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 193-193: code points 1-92
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 192-193: code points 1-92

Examples:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 195-196: code points 1-0

\begin{itemize}
\item If green time is 40 seconds, the station must be at least 100 meters from the intersection, equal the length of queue discharged during the green time:% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 196-197: code points 1-53
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 196-197: code points 1-53

$ \text{Dist}_\text{station-intersection} [\text{in meters}] \geq 2.5 * 40 = 100 $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 199-199: code points 1-84

\begin{itemize}
\item If green time is 90 seconds, the station must be at least 225 meters from the intersection, equal the length of queue discharged during the green time:% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 201-202: code points 1-53
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 201-202: code points 1-53

$ \text{Dist}_\text{station-intersection} [\text{in meters}] \geq 2.5 * 90 = 225 $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 204-204: code points 1-84

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/b8fcc541518c6723be9019099a7aa8d1783b117a.jpeg}
		\fignote{24}{Diagram of the distance between the station and the signalized intersection (Diststation-intersection shown as Dbs).\label{chapter:intersections-and-signal-control:figure:diagram-of-the-distance-between-the-station-and-the-signalized-intersection-diststation-intersection-shown-as-dbs}}{ITDP.}
	}
\fi

\subsection{4}{Minimizing the Recommended Distance between the BRT Station and the Intersection from a BRT Perspective}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:station-location-relative-to-the-intersection:subSection:minimizing-the-recommended-distance-between-the-brt-station-and-the-intersection-from-a-brt-perspective}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 209-285: code points 1-56

Another compelling reason for separating the station and the intersection is that it minimizes the risk that BRT vehicles will be backed up at the station, which will inhibit the functioning of the intersection and the functioning of the station. If these two potential bottlenecks are co-located, the risk of mutual interference between the station and the intersection increases. Consequently, it is advised to include a safety buffer in the station design for those stations to be located near a signalized intersection. This additional length will temporarily hold buses that: (1) in case of a blockage have cleared the station but are forced to queue up at the intersection until the conflict is resolved, or (2) have cleared the station during the red phase and have to wait for the green phase (Figure 24.25 and Figure 24.26). This buffer should also be around a hundred meters, as the following equations show.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 211-219: code points 1-79

This problem is still serious in “open” BRT systems without clearly designated stopping bays, as bus queueing can be longer than the platform. Besides that, such systems can cause a chaotic boarding process that not only creates stress for the customer but also increases boarding times (Figure 24.27).\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 221-223: code points 1-95

\ifxetex
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\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/7a6c5affa21c2ea0d3cec88bd5232c1e4de3cdfe.png}
		\fignote{25}{For the direction of the BRT system that stops at the station before the intersection, there is a risk that vehicles will be delayed due to the signal phase.\label{chapter:intersections-and-signal-control:figure:for-the-direction-of-the-brt-system-that-stops-at-the-station-before-the-intersection-there-is-a-risk-that-vehicles-will-be-delayed-due-to-the-signal-phase}}{ITDP.}
	}
\fi

\ifxetex
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	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/b5bc55e942064a70165a3240a012b398d414fc46.png}
		\fignote{26}{For the direction of the BRT system that stops after the intersection, there is a risk that vehicles create a backup into the intersection and block traffic.\label{chapter:intersections-and-signal-control:figure:for-the-direction-of-the-brt-system-that-stops-after-the-intersection-there-is-a-risk-that-vehicles-create-a-backup-into-the-intersection-and-block-traffic}}{ITDP.}
	}
\fi

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\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/4217dcb8bd6de3bf14d06ea0f40c07a6bddf6e9a.jpeg}
		\fignote{27}{For the direction of the BRT system that stops after the intersection, there is a risk that vehicles create a backup into the intersection and block traffic.\label{chapter:intersections-and-signal-control:figure:for-the-direction-of-the-brt-system-that-stops-after-the-intersection-there-is-a-risk-that-vehicles-create-a-backup-into-the-intersection-and-block-traffic}}{ITDP}
	}
\fi

The buffer size (Dist\textsubscript{station-intersection}) should be the space required by queuing BRT vehicles.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 234-235: code points 1-24

$ \text{Dist}_\text{station intersection} \geq N_\text{vehicle} * \text{Length}_\text{vehicle} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 237-237: code points 1-98

Where:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 239-240: code points 1-0

\begin{itemize}
\item {$ \text{Length}_\text{vehicle} $: Average length of lane space consumed by the queuing BRT vehicles; adding two values:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 240-241: code points 8-0

\begin{itemize}
\item Length of the BRT vehicle;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 241-242: code points 1-0
\item Length of space between BRT vehicles when stopped (usually assumed to be 1 meter).% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 242-242: code points 1-88
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 241-242: code points 1-88

}
\item $ N_\text{vehicle} $: Likely number of vehicles to queue during the red phase ($T_\text{red}$) of traffic signal, discussed below.% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 243-244: code points 1-6
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 240-244: code points 1-6

Assuming BRT vehicle frequencies ($ \text{Freq}_\text{bus}$) are 50 percent below the BRT lane saturation flow ($\text{SaturationFlow}_\text{bus}$) – that happens practically always, as this represents 360 articulated buses per hour that would carry more than 40,000 customers per hour per direction – $ N_\text{bus} $, which is equivalent to the height of the upper graphic in Figure 24.7, can be determined by:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 246-249: code points 1-37

Eq. 24.20\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 251-251: code points 1-9

$ N_\text{vehicle} = {T_\text{red} * \text{Freq}_\text{vehicle} \over ({1 - \text{Freq}_\text{vehicle} \over  \text{SaturationFlow}_\text{vehicle} })} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 253-253: code points 1-154

Where:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 255-256: code points 1-0

\begin{itemize}
\item $ N_\text{vehicle} $: Number of vehicles;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 256-257: code points 1-0
\item $ T_\text{red} $: Time given by a red light holding traffic from crossing an intersection;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 257-258: code points 1-0
\item $ \text{Freq}_\text{vehicle} $: BRT vehicle frequency;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 258-259: code points 1-0
\item $ \text{SaturationFlow}_\text{vehicle} $: Maximum flow BRT lane can handle;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 259-259: code points 1-83
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 256-259: code points 1-83

\emphasis{Example utilizing typical data of an average city in India:}\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 261-261: code points 1-61

\begin{itemize}
\item T\textsubscript{red} = 50 seconds (or 50\slash{}3,600 hours to use consistent units = 1\slash{}72 hour);% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 263-264: code points 1-0
\item Freq\textsubscript{vehicle} = 200 articulated-buses \slash{} hour (equivalent to 1 vehicle each 18 seconds);% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 264-265: code points 1-0
\item SaturationFlow\textsubscript{vehicle} = 720 articulated buses \slash{} hour (one lane, equivalent to 1 vehicle each 5 seconds);% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 265-267: code points 1-0
\item Length\textsubscript{vehicle} = 19.5 meters (18.5 meters + 1 meter).% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 267-267: code points 1-65
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 263-267: code points 1-65

$ N_\text{vehicle} = {{50 \over 3600} *200 \over 1 – (200 / 720)}  = 3.8 \text{vehicles} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 269-269: code points 1-92

Because one cannot actually have 3.8 buses queueing, $_\text{Nvehicle}$ must be rounded to the nearest integer, so it is equal to 4.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 271-272: code points 1-17

$ \text{Dist}_\text{station-intersection} \geq N_\text{vehicle} * \text{Length}_\text{vehicle} $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 274-274: code points 1-98

$ \text{Dist}_\text{station-intersection} \geq 4 * 19.5 $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 276-276: code points 1-59

$ \text{Dist}_\text{station-intersection} \geq 78 $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 278-278: code points 1-53

Thus, the minimum recommended distance between the BRT station and the intersection would be 78 meters.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 280-280: code points 1-103

BRT systems currently in operation prove that mixed traffic misbehavior is a relevant source of operation disruptions throughout the public transport system. Traffic spillbacks are commonly seen in heavily congested intersections blocking perpendicular movements along the BRT corridor, so it may be proper to analyze the tolerance; space needed is proportional to red time.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 282-285: code points 1-56

\subsection{5}{Optimizing Walking Distances}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:station-location-relative-to-the-intersection:subSection:optimizing-walking-distances}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 287-403: code points 1-0

As mentioned in the introduction to this section, the willingness to place a station close to the intersection under the excuse of reducing walking times is rarely based on data. In the rare case of low-density areas with few clear origin-destinations where demand is known, the optimal spot can be easily determined. Such locations are not likely to be near busy intersections, and in the event that they are and the intersection is clearly the best location from the perspective of reducing walking time, it is more likely that it is better to move the station back at the length of a few buses than risk hindering the station. That can be perceived considering only the customer that intends to alight in that location: he or she may need an extra minute to walk to the intersection and would need an extra minute inside the vehicle stuck in the station because the vehicle in front is waiting for the green signal. If we consider that all the other customers not alighting there will increase their travel time by one minute and that the queue is likely to get longer (and everyone will wait more than one minute), then it is clear that the station should be moved away from the intersection.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 289-300: code points 1-43

The previous paragraph makes clear that, in high-density areas, to optimize station location with high precision requires labor-intensive, site-specific surveys, and analysis of the origins and destinations must be performed taking into consideration a pedestrian path network encompassing an area within a radius of one thousand meters or more from the possible extremes where the station can be placed. Additionally, several different street crossings should be looked at as well as the placement of other stations. That is, make the simulation model detailed to the level that every block face is a centroid, if not every address.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 302-308: code points 1-8

Our limited experience with such endeavors on central areas has shown that moving a station within a range of two hundred meters has no noticeable effect. But It should be remembered that \emphasis{changing the number of stations within a given corridor extension has a significant impact on overall travel time}; that impact is determined by the average distance between the stations as discussed in Chapter 7: Capacity and Speed and requires a much less detailed survey and analysis.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 310-314: code points 1-64

\emphasis{Correction Factor for Station Saturation at Traffic Light}\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 316-316: code points 1-59

Chapter 7: Capacity and Speed discusses at length the \emphasis{level of saturation of the station, or the proportion of time that BRT vehicles are blocking the station}. In particular, mid-block stations are likely to be accessible by at-grade crossings right in front of them. It is generally advisable to investigate the degree to which this intersection increases the saturation of the station.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 318-321: code points 1-78

Roughly, the combination of the station’s normal saturation (which we will call Xstation) and the additional saturation caused by traffic signal interference will reveal the degree of busway saturation. As a general rule, it is best to design the station with a saturation level of under 0.4 at the station, meaning that the station is occupied only 40 percent of the time.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 323-326: code points 1-52

A correction factor that estimates what would be the new level of saturation of the station if the traffic light is positioned right in front of it (X\textsubscript{is0}) can be expressed in function of:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 328-329: code points 1-94

\begin{itemize}
\item Signal cycle time ($T_\text{cycle}$);% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 331-332: code points 1-0
\item Signal red time for the BRT approach ($T_\text{red}$);% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 332-333: code points 1-0
\item Average stop time per bus in the station composed by dwell, boarding, and alighting times ($T_\text{station}$).% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 333-333: code points 1-119
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 331-333: code points 1-119

\emphasis{Correction for a Long Red Phase (T\textsubscript{station} < T\textsubscript{red})}\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 335-335: code points 1-63

The relation between Tred and Tstation is the most important; the concern about interference is most acute when the bus stopping time (TB) is short and the red phase (TR) is longer, or of a similar magnitude. Interference is only of limited concern if the red phase is very short.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 337-339: code points 1-71

In this case, to calculate the saturation of the station when faced with interference from the traffic signal, the following formula can be used:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 341-342: code points 1-42

Eq. 24.21\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 344-344: code points 1-9

$ X_{is0} ={ X_\text{station} * T_\text{cycle} \over  T_\text{cycle}- T_\text{red} + 0.5*TB } $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 346-346: code points 1-97

Where:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 348-349: code points 1-0

\begin{itemize}
\item $ X_\text{is0} $:Correction factor that estimates what would be the new level of saturation of the station if the traffic light is positioned right in front of it;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 349-351: code points 1-0
\item $ X_\text{station} $: Station’s normal saturation level;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 351-352: code points 1-0
\item $ T_\text{cycle} $: Time given by the signal cycle;Tred = Time given by a red light holding traffic from crossing an intersection;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 352-353: code points 1-0
\item $ TB $: Bus stopping time.% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 353-353: code points 1-34
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 349-353: code points 1-34

\emphasis{Correction with a Short Red Phase (T\textsubscript{station} ≥ T\textsubscript{red})}\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 355-355: code points 1-65

If the red signal phase is very short relative to the boarding and alighting time, then even if the signal changes to red just as boarding and alighting has been completed, it will be a short time before the light is green again. Thus, there is less concern about interference between the station and the intersection.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 357-360: code points 1-13

Eq. 24.22\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 362-362: code points 1-9

$ X_{is0} = {X_\text{station} *T_\text{cycle} \over T_\text{cycle}-{T_\text{red}^2 \over 2 * T_\text{station}} }$\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 364-364: code points 1-115

Where:\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 366-367: code points 1-0

\begin{itemize}
\item $ X_{is0} $: Correction factor that estimates what would be the new level of saturation of the station if the traffic light is positioned right in front of it;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 367-369: code points 1-0
\item $ X_\text{station} $: Station’s normal saturation level;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 369-370: code points 1-0
\item $ T_\text{cycle} $: Signal cycle time;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 370-371: code points 1-0
\item $ T_\text{red} $: Signal red time for the BRT approach;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 371-372: code points 1-0
\item $ T_\text{station} $: Average stop time per bus in the station composed by dwell, boarding, and alighting times.% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 372-372: code points 1-120
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 367-372: code points 1-120

Examples\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 374-374: code points 1-8

\highlight{1. Calculating station to intersection interference with a long red phase}\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 376-376: code points 1-85

$ X_{is0} ={ X_\text{station} * T_\text{cycle} \over  T_\text{cycle}- T_\text{red} + 0.5*TB } $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 378-379: code points 1-0

\begin{itemize}
\item X\textsubscript{station} = 0.35;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 379-380: code points 1-0
\item T\textsubscript{cycle} = 700 seconds;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 380-381: code points 1-0
\item T\textsubscript{red} = 500 seconds;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 381-382: code points 1-0
\item T\textsubscript{station} = 10 seconds.% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 382-382: code points 1-34
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 379-382: code points 1-34

$ X_{is0} ={ 0.35 * 700 \over  700 \text{seconds} - 500 \text{seconds}  + 0.5* 10 \text{seconds} } = 1.195 $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 384-384: code points 1-110

In this hypothetical example the station would operate on just the 200 seconds of green, but not on the 500 seconds of red, because just some seconds after the red phase begins the bus will finish boarding, but it will obstruct access to the bus stop during the entire 500 seconds of red. Thus, at a value of 1.195 the high saturation leads to considerable congestion of the busway.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 386-389: code points 1-73

\highlight{2. Calculating station to intersection interference with a short red phase}\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 391-391: code points 1-86

$ X_{is0} = {X_\text{station} *T_\text{cycle} \over T_\text{cycle}-{T_\text{red}^2 \over 2 * T_\text{station}} }$\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 393-394: code points 1-0

\begin{itemize}
\item $X_\text{station} = 0.35$;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 394-395: code points 1-0
\item $T_\text{cycle} = 30 \text{seconds full signal phase}$;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 395-396: code points 1-0
\item $_\text{Tred} = 15 \text{seconds of red phase}$;% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 396-397: code points 1-0
\item $ _\text{Tstation} = 40 \text{seconds of vehicle stopping time}$.% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 397-397: code points 1-73
\end{itemize}
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 394-397: code points 1-73

$ X_{is0} = {0.35 * 30  \over 30 - {15^2 \over 2 * 40} } = 0.386 $\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 399-399: code points 1-68

In this case, because the red phase is quite short, there is fairly minimal risk that the traffic signal will disrupt the functioning of the bus stop, so saturation increases only marginally, from 0.35 to 0.386.\par
% @ guide/24-intersections_and_signal_control/station-location-relative-to-the-intersection.src: lines 401-403: code points 1-0

\section{5}{Restricting General Traffic Turning Movements}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 1-765: code points 1-0

\quotation{No matter how many times you save the world, it always manages to get back in jeopardy again. Sometimes I just want it to stay saved! You know, for a little bit? I feel like the maid; I just cleaned up this mess! Can we keep it clean for . . . for ten minutes!}{Mr. Incredible (Craig T. Nelson), The Incredibles, 2004}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 3-4: code points 1-57

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/856b61cbec64e00de10176e4c00ac14b01611156.png}
		\fignote{28}{Exchanging width between entrance and exit sections where turning volumes are high enough to allow the change to improve capacity meaningfully.\label{chapter:intersections-and-signal-control:figure:exchanging-width-between-entrance-and-exit-sections-where-turning-volumes-are-high-enough-to-allow-the-change-to-improve-capacity-meaningfully}}{Elebeta.}
	}
\fi

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/0b84e85346dacb76ce751ddd3bd991eb04c8e5d2.jpeg}
		\fignote{29}{Cape Town, South Africa’s standard four-phase intersection with a cross-traffic-turn waiting area using the narrowed width of the opposite way.\label{chapter:intersections-and-signal-control:figure:cape-town-south-africas-standard-four-phase-intersection-with-a-cross-traffic-turn-waiting-area-using-the-narrowed-width-of-the-opposite-way}}{Bruce Sutherland.}
	}
\fi

The overall capacity of the intersection is given by the sum of the capacity of each approaching lane. By its turn, the capacity of each approaching lane is given by the sum of saturation flow of the lane multiplied by the sum of the relative green times of the phases for when the lane is active.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 12-14: code points 1-92

No matter how many phases there are on the traffic light, the sum of relative green for all vehicular phases with relative lost time is constant (if there were no pedestrian phases, it would be equal to one). The initial step to programming traffic lights is to divide this fixed amount among the phases with the general assumptions that (1) a movement not allowed during a given phase will block a lane and (2) that the saturation flow per lane is the same (for turning it can be lower): \emphasis{for any given signalized intersection, if a phase is removed (therefore the movements of that phase are removed) and the green time including the approaches for the movements of the removed phase are included into another phase (both in the same phase), then the overall capacity of the intersection will necessarily increase.}\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 16-23: code points 1-99

This is empirically clear for a user arriving in a balanced intersection, since a larger number of phases in a traffic light means waiting longer and having a lower share of green time.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 25-26: code points 1-86

Of course it is not interesting to create capacity for movements without demand. The following subsections will discuss alternatives to divert traffic in order to increase capacity by eliminating phases. We will see that in some cases, intersection capacity is still increased even if the demand for some eliminated movements, namely cross-traffic turns, are forced to pass over the intersection twice.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 28-31: code points 1-86

Widening the intersection can be of great assistance, but doing it alone rarely can achieve the same benefits of reducing phases from four to two. In a relatively normal situation where turning volumes are large enough to the point that after the intersection the straight flow can fit in one less lane than before the intersection (as discussed in Section 24.4.2: Minimizing the Number of Mixed-Traffic Lanes Away from the Intersection), it is possible to narrow the exiting section, allowing the entrance section of the opposite way to be broader (Figures 24.28 and 24.29); the extra width can be useful for mixed traffic, enhancing mixed-traffic capacity, or to allow BRT turning movements where required (see Section 24.6: Allowing BRT Turns).\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 33-40: code points 1-34

\beginbox{1}{Narrowing lanes}
\label{chapter:intersections-and-signal-control:box:narrowing-lanes}
Narrowing lanes is a recognized traffic calming measure and a possible way to increase the intersection approach capacity. Even though the saturation flow will be reduced in each lane, if one more lane can be squeezed into the stop line, capacity may increase and a better use of space for queueing may be provided.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 44-46: code points 1-109

Places where congestion is a serious issue may already have addressed regulation that allows using narrow measures, and, if not, public works guidelines have to be changed.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 48-49: code points 1-73

The United States Federal Highway Administration suggests that, despite the desired lane width of 3.6 meters to maximize flow, right-of-way or pedestrian needs may dictate use of a narrower lane width; lane widths below 2.7 meters are not recommended for new design, but in some very constrained retrofit situations on low-speed roadways, lane widths as low as 2.4 meters should be considered where appropriate (Figure 24.30).\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 51-55: code points 1-7

\ifxetex
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		\img{\hsize}{infrastructure/assets/8c83c36f90757172da9a488bd4ecc2a1c7bcc684.png}
		\fignote{30}{Lanes as narrow as 2.4 meters are an effective way to improve intersection capacity, as in this intersection in Montgomery County, Maryland, USA.\label{chapter:intersections-and-signal-control:figure:lanes-as-narrow-as-24-meters-are-an-effective-way-to-improve-intersection-capacity-as-in-this-intersection-in-montgomery-county-maryland-usa}}{Google Earth.}
	}
\fi

\endbox
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 42-60: code points 1-7

\subsection{1}{Eliminating Intersections}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:eliminating-intersections}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 62-164: code points 1-48

\ifxetex
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		\img{\hsize}{infrastructure/assets/e235c0a934e5cc7811402d7612aa4b4853f7bc15.jpeg}
		\fignote{31}{Prior to Quito’s Ecovía line, mixed-traffic vehicles were allowed to cross through this intersection as well as negotiate cross-traffic and curbside turns. To give priority to public transport, crossing straight and cross-traffic turn movements have been blocked.\label{chapter:intersections-and-signal-control:figure:prior-to-quitos-ecova-line-mixed-traffic-vehicles-were-allowed-to-cross-through-this-intersection-as-well-as-negotiate-cross-traffic-and-curbside-turns-to-give-priority-to-public-transport-crossing-straight-and-cross-traffic-turn-movements-have-been-blocked}}{Lloyd Wright.}
	}
\fi

The extreme case of reducing phases would only allow for one phase, which would be equivalent to eliminating the intersection itself, clearly increasing capacity.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 69-70: code points 1-53

Thus eliminating intersections along the busway seems at first a good idea. For median-side busways this can be done by simply forbidding cross traffic, while still allowing flow from the transversal street to join the mixed traffic in the corridor at the curbside as in Figure 24.31, providing access to the corridor.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 72-75: code points 1-9

The flaw in adopting such an extreme solution is that eliminating phases is based on diverting traffic demand in favor of the exclusive movements, so its movement can be done with other flows. Eliminating the movement (in this case, crossing the corridor) does not eliminate the demand for it; the movement has to happen somewhere else.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 77-80: code points 1-29

This measure will reduce accessibility when applied without discretion and will concentrate crossing demand in a few locations (Figure 24.32). Before eliminating an intersection, it is necessary to understand which alternative paths the demand will use to cross the corridor and compare the impacts of both situations: if the volumes are low or if the alternatives will not generate more delay to the BRT, then it really is a good idea to eliminate the intersection. Eventually, it will become necessary to create new intersections to split conflicting volume of one intersection into several to increase green times for the BRT.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 82-87: code points 1-97

\ifxetex
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		\img{\hsize}{infrastructure/assets/b438bee6afe09c669bb795bef2ea05edb71581bc.png}
		\fignote{32}{Closing intersections reduces accessibility, and may lead to harder to handle intersections. With no stations, BRT vehicles can benefit from signal coordination.\label{chapter:intersections-and-signal-control:figure:closing-intersections-reduces-accessibility-and-may-lead-to-harder-to-handle-intersections-with-no-stations-brt-vehicles-can-benefit-from-signal-coordination}}{Elebeta.}
	}
\fi

If there are no stations in the surrounding area, then BRT vehicles can pass through several intersections at once if a synchronized signal system is used (see Section 24.1.3: Traffic Signal Concepts and Section 24.3.1 Passive Signal Priority). However, when there are stations between intersections, the BRT vehicle will pass through the green phase at the first intersection and then stop at the station for customer boarding and alighting. By the time the vehicle resumes movement toward the second intersection, the signal phase may have changed to red (Figure 24.33).\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 92-97: code points 1-52

\ifxetex
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		\fignote{33}{Coordination for mixed traffic does not help the BRT corridor when there is a station between intersections. If the green time of the green wave has the same length of total dwell time at stations, the effect can be particularly harmful, as it increases the chances that the BRT vehicle’s arrival at an intersection after a station will be during the red time.\label{chapter:intersections-and-signal-control:figure:coordination-for-mixed-traffic-does-not-help-the-brt-corridor-when-there-is-a-station-between-intersections-if-the-green-time-of-the-green-wave-has-the-same-length-of-total-dwell-time-at-stations-the-effect-can-be-particularly-harmful-as-it-increases-the-chances-that-the-brt-vehicles-arrival-at-an-intersection-after-a-station-will-be-during-the-red-time}}{ITDP.}
	}
\fi

But when intersections are too close together in order to optimize the station location relative to them, an assessment has to be made regarding how important the station location is for boarding and alighting customers, the detour forced on mixed traffic close to the station, and to what extent it hinders the whole BRT system due to interference between the station and the intersection. There are three options:\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 104-107: code points 1-103

\begin{enumerate}
\item Close one of the intersections: this generates mixed-traffic detour time and higher cross volumes at other points that may impact the BRT corridor as well;% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 109-111: code points 1-0
\item Transfer or remove the station: this increases walking time for BRT users of that station;% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 111-112: code points 1-0
\item Keep station and intersections: this generates delay for all customers in the BRT that pass through the intersection.% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 112-113: code points 1-17
\end{enumerate}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 109-113: code points 1-17

Even for normal mixed traffic, having two intersections too close together will sometimes lead to problems of the same nature as discussed in Section 24.4.2: Minimizing the Number of Mixed-Traffic Lanes Away from the Intersection and Section 24.4.3: Minimizing the Recommended Distance between the BRT Station and the Intersection from a Mixed-Traffic Perspective vehicles queued at one intersection will back up to the point where vehicles are unable to clear the previous intersection during a green phase. Equation 24.22 below defines the calculation for the distance above which this type of conflict shall not occur.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 115-120: code points 1-103

Eq. 24.23\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 122-122: code points 1-9

$ D_{i1-i2} \geq 3 * Max(T_\text{green-i1},T_\text{green-i2}) $\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 124-124: code points 1-65

Where:\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 126-127: code points 1-0

\begin{itemize}
\item $ D_\text{i1-i2} $: Distance in meters between intersection 1 and intersection 2;% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 127-128: code points 1-0
\item $ T_\text{green-i1} $: Green signal time in seconds at intersection 1;% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 128-129: code points 1-0
\item $ T_\text{green-i2} $: Green signal time in seconds at intersection 2.% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 129-129: code points 1-78
\end{itemize}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 127-129: code points 1-78

A mixed-traffic lane can generally handle 1,800 vehicles per hour. This quantity translates to two vehicles per second (3,600 seconds in an hour). When vehicles are stopped at a stoplight, the average amount of space they take up is 6 meters; this space includes the vehicle and some space between vehicles. This average vehicle distance means that for each second of time, 3 meters of vehicle-equivalents can be moved through the intersection.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 131-135: code points 1-34

This distance between the intersections guarantees that there is enough space for queueing vehicles, so that it does not happen that the green light is open and there are vehicles stuck in the upstream traffic light. Proper synchronization can reduce this distance to practically zero.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 137-139: code points 1-83

\emphasis{Example}\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 141-141: code points 1-9

The following scenario is outlined in order to determine whether two intersections 100 meters apart will result in free-flow operation or in congestion:\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 143-145: code points 1-0

\begin{itemize}
\item D\textsubscript{i1-i2} = 100 meters;% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 145-146: code points 1-0
\item T\textsubscript{green-i1} = 50 seconds;% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 146-147: code points 1-0
\item T\textsubscript{green-i2} = 30 seconds.% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 147-147: code points 1-35
\end{itemize}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 145-147: code points 1-35

To determine if the distance between these intersections is sufficient, Equation 24.19 can be applied:\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 149-149: code points 1-102

$ 100 \geq 2.5 * Max(50,30) $\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 151-151: code points 1-31

$ 100 \geq 150 \leftarrow \text{FALSE} $\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 153-153: code points 1-42

Since 100 meters is less than the required 150 meters, there is not enough space between the intersections.\par
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In the direction from 1 to 2 it is possible (if 2 is red while 1 is green) that vehicles queuing at 2 will back up onto the first intersection and the last 50 meters of queue will be trapped before intersection 1.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 158-160: code points 1-2

In the direction from 2 to 1 it is possible (if 1 green starts the same time the first vehicle from 2 arrives at the intersection), then the last 20 seconds of green in 1 will be useless, since vehicles stop flowing after 30 seconds in intersection 2.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 162-164: code points 1-48

\subsection{2}{Shortening and Eliminating Phases}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 166-365: code points 1-94

In this subsection we name traffic diversion models and traffic sign phase schemes as we describe them in order to refer to them in the following text and in the next subsection.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 168-169: code points 1-75

\subsubsection{1}{Typical 4-Phase-Intersection}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:typical-4-phase-intersection}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 171-190: code points 1-118

In a typical intersection that allows all movements (Figure 24.34), four phases are required; usually each origin has its phase (“standard-four-phase”) but an alternative scheme with one phase for each direction (two ways) in straight movement and curbside turns, and one phase for each direction (two ways), cross-traffic turn may be used as well, which we will refer to as the “symmetrical phase.”\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 173-176: code points 1-76

The standard configuration has the advantage of not requiring dedicated queue space (queue box) for cross-traffic turns and also allow sharing one lane for cross-turn and straight movements (it can be the most median-side or the second closest to it) and let the intensity of the flow variations along the day balance the use of this lane. The symmetrical phases are interesting when cross-traffic-turn flows are relatively low and straight movements are intense in both ways (cross-traffic-turn phase will be short and straight will be long). Our practical experience suggests that symmetrical tends to be better if a clear bidirectional flow exists, but it ultimately requires an assessment of the flows intensity to each application.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 178-185: code points 1-20

A combination of the two is also possible, using cross-traffic-turn phase for one direction, and one phase per origin in the other direction (“mixed-four-phase”).\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 187-188: code points 1-61

\ifxetex
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		\img{\hsize}{infrastructure/assets/6b91592bae0c2b7d2e661868060969c2f3ba01e3.jpeg}
		\fignote{34}{Possible movements and signal phases at a typical four-leg intersection.\label{chapter:intersections-and-signal-control:figure:possible-movements-and-signal-phases-at-a-typical-four-leg-intersection}}{ITDP.}
	}
\fi

\subsubsection{2}{Movements Conflicting with BRT}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:movements-conflicting-with-brt}
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		\img{\hsize}{infrastructure/assets/b8a418aec8c198eab974dd5dbe096b3c90a2c3ed.jpeg}
		\fignote{35}{Along Quito’s Central Norte corridor, vehicles in mixed traffic are given a phase to perform left turns. Image\label{chapter:intersections-and-signal-control:figure:along-quitos-central-norte-corridor-vehicles-in-mixed-traffic-are-given-a-phase-to-perform-left-turns-image}}{Lloyd Wright.}
	}
\fi

When the BRT has to cross a typical four-stage intersection, the main concern is to increase the green time for the corridor direction. Eliminating phases are likely to be very effective in doing so, but it is important to keep in mind that it is not the primary goal. Eliminating phases in a way that green time is not increased for the BRT approaches will improve only mixed-traffic performance.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 197-200: code points 1-89

To eliminate the phases we must focus on the \emphasis{movements that conflict with the BRT} (Figure 24.36) and try to reroute them in such a way that they can cross the corridor in one phase and briefly—that is, providing width to the crossing movement approaches. Providing width to parallel movements is important to improving general traffic, which is also desirable, but not paramount.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 202-205: code points 1-73

\emphasis{For the remainder of the section we will assume that the busway is median-side aligned and that the busway crosses the intersection straight; if the busway is curbside and\slash{}or it is turning between perpendicular roads, the same reasoning applies and the same alternatives for detour mixed-traffic movements will be considered, but in a different and appropriated way.}\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 207-210: code points 1-53

With a median-side BRT, standard-four-phase sign can no longer be applied, as it will conflict with the cross-traffic turn (Figure 24.35), so the symmetrical or the mixed-four-phase has to be used.\par
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\ifxetex
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		\img{\hsize}{infrastructure/assets/01ba165e1a2b3b697638f4b65a0b64e21ba59837.jpeg}
		\fignote{36}{With the insertion of BRT (red) in a four-stage signal, the cross-traffic turn from the same direction needs to have its own phase.\label{chapter:intersections-and-signal-control:figure:with-the-insertion-of-brt-red-in-a-four-stage-signal-the-cross-traffic-turn-from-the-same-direction-needs-to-have-its-own-phase}}{Elebeta.}
	}
\fi

\subsubsection{3}{Diverting Curbside Turns}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:diverting-curbside-turns}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 218-234: code points 1-30

Diverting curbside turns does not remove a phase, but it can free space for queueing and increase capacity for the remaining movements.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 221-222: code points 1-28

Moving curbside turns away from the intersection is usually simple if parallel streets are available (Figure 24.37). It will require a cross-traffic turn in the parallel street corner, which may start to spread the main corridor intersection problems to a broader area. Detouring the curbside flow from the crossing street is particularly interesting because it can leave the width of the whole approach available to conflict movements, reducing the crossing time (red for the corridor) in the same proportion this curbside-turn flow is to the total flow, even if four phases are in use. From a BRT point of view, there is no interest in diverting the parallel curbside flow at the intersection, as it is not a conflicting movement.\par
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\ifxetex
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		\fignote{37}{Curbside-turn detour can leave width in the main intersection available to crossing flows.\label{chapter:intersections-and-signal-control:figure:curbside-turn-detour-can-leave-width-in-the-main-intersection-available-to-crossing-flows}}{Elebeta.}
	}
\fi

\subsubsection{4}{Diverting Cross-Traffic Turns}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:diverting-cross-traffic-turns}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 236-241: code points 1-92

There are several ways of eliminating cross-traffic turns in the main intersection by detouring the flow. These can be applied both to the flows parallel to the corridor and to the flows crossing the corridor (and turning parallel to it). Without cross-traffic turns, the intersection can have only two phases, but applying a detour to only one direction (both ways) means eliminating one phase already.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 238-241: code points 1-92

\subsubsection{5}{Curbside-Turn, Cross-Traffic Turn, and Cross-Traffic Turn (“curb-first”)}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:curbside-turn-cross-traffic-turn-and-cross-traffic-turn-curb-first}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 243-253: code points 1-86

This detour follows a curbside detour proposed through auxiliary streets, with a curbside turn at the parallel street before the intersection, followed by two successive cross-traffic-side turns (Figure 24.38). This variation is more effective to apply to the corridor perpendicular to the BRT, as it frees width in its main approach to straight flow only. When compared with other alternatives (discussed below) this detour might be more beneficial to mixed traffic as opposed to the BRT, since it may justify reduction of proportional green time in BRT’s direction.\par
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		\fignote{38}{By detouring a cross-traffic turn to a curbside parallel street before reaching the intersection, a phase is eliminated in the main intersection.\label{chapter:intersections-and-signal-control:figure:by-detouring-a-cross-traffic-turn-to-a-curbside-parallel-street-before-reaching-the-intersection-a-phase-is-eliminated-in-the-main-intersection}}{Elebeta.}
	}
\fi

\subsubsection{6}{Loop}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:loop}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 255-267: code points 1-41

For the loop, the flow looking to perform a cross-traffic turn has to instead cross straight through the intersection and perform three curbside turns and then cross straight through the intersection again (Figure 24.39 shows an application of this flow that is initially parallel to the BRT), even though this has the clear disadvantage of using the intersection twice. Although the other way can be better, this alternative is always interesting for the BRT crossing flow, because it necessarily reduces red times. For the parallel flow it is interesting while flows are low enough not to take one lane width on the crossing-BRT phase.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 257-263: code points 1-19

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		\fignote{39}{Three curbside turns after crossing the intersection is a simple alternative to eliminating cross-traffic turns; despite crossing the intersection twice, it does not create much conflict with existing flows.\label{chapter:intersections-and-signal-control:figure:three-curbside-turns-after-crossing-the-intersection-is-a-simple-alternative-to-eliminating-cross-traffic-turns-despite-crossing-the-intersection-twice-it-does-not-create-much-conflict-with-existing-flows}}{Elebeta.}
	}
\fi

\subsubsection{7}{Previous Cross Turn (“previous cross”)}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:previous-cross-turn-previous-cross}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 269-298: code points 1-82

Before reaching the main intersection, the diverted flow is allowed to cross-traffic turn in a location where there is no perpendicular crossing traffic (i.e., where previously no crossing intersection existed), the opposite straight flow has to be detained to allow this move, but it can be stopped synchronously to the main intersection. After the cross, the diverted flow follows perpendicular to the main corridor until a suitable location for a curbside turn is reached; from there it will run parallel to the original flow in the direction of another intersection in the crossing road, downstream the main intersection, where it will join the flow by means of another cross-traffic flow in a two-stage traffic light (where previously no crossing existed or now has to be forbidden) also synchronized with the main intersection (Figure 24.40).\par
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		\img{\hsize}{infrastructure/assets/e5a4c0cd5761d4283d74b237f27e13dc4d1cd357.png}
		\fignote{40}{It is possible to provide a two-phase coordination for detouring cross-side turns to leave the road upstream and return downstream of the main intersection; additional synchronized traffic lights are required.\label{chapter:intersections-and-signal-control:figure:it-is-possible-to-provide-a-two-phase-coordination-for-detouring-cross-side-turns-to-leave-the-road-upstream-and-return-downstream-of-the-main-intersection-additional-synchronized-traffic-lights-are-required}}{Elebeta.}
	}
\fi

The “previous cross” detour is the best alternative for the parallel flow to the BRT corridor that wants to turn across traffic on the main intersection because it definitely moves the conflict away from the most crowded intersection. But it cannot be applied in both directions (parallel and perpendicular) as it would require a three-phase intersection for exiting\slash{}returning to the main avenues. It also may create capacity conflict if, in the perpendicular direction of approach, the curbside-turn is being diverted, so consideration should be taken to redirect it back to regular curbside turning at the intersection. If cross-traffic turn, also in the perpendicular direction, is diverted by means of the “curbside first,” then serious conflict would rise, so the perpendicular flow shall be redirected to a “loop.”\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 285-292: code points 1-92

The previous cross alternative is similar in concept to the “displaced left-turn” intersection in the United States (Figure 24.41), which can be applied where width is available.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 294-295: code points 1-76

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		\fignote{41}{In the United States, the concept of previous turn is applied in a less dense urban context by the name of “displaced left turn” intersection.\label{chapter:intersections-and-signal-control:figure:in-the-united-states-the-concept-of-previous-turn-is-applied-in-a-less-dense-urban-context-by-the-name-of-displaced-left-turn-intersection}}{Elebeta.}
	}
\fi

\subsubsection{8}{Curbside Turn and U-Turn (“curb-u”)}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:curbside-turn-and-u-turn-curb-u}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 300-315: code points 1-113

A cross-traffic-flow detour is made by first making a curbside turn at the crossing road, followed by a U-turn in the crossing road at a suitable location approximately one hundred meters from the major route, and then driving straight through the intersection. From the main intersection capacity point of view, this alternative has no advantage over the loop as it takes away the same width as the loop in both approaches. It is suitable when the loop is not an option, because the alternative is already congested or too long, which would create political problems with car drivers; besides, there would have to be sufficient width to accommodate the U-turn as well as length for a waiting area. To be applied to the traffic coming from the perpendicular direction to the BRT, as this movement crosses the bus lanes it creates undesirable conflicts for the BRT system. The U-turn traffic light should be two-phase only, synchronized with the main intersection.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 302-311: code points 1-40

\ifxetex
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		\fignote{42}{Making a U-turn after entering, by means of a curbside turn, the opposite way of the desired direction is another way to perform a cross-traffic turn without need of an exclusive phase. This alternative requires a queueing area and uses two approaches to the intersection as well.\label{chapter:intersections-and-signal-control:figure:making-a-u-turn-after-entering-by-means-of-a-curbside-turn-the-opposite-way-of-the-desired-direction-is-another-way-to-perform-a-cross-traffic-turn-without-need-of-an-exclusive-phase-this-alternative-requires-a-queueing-area-and-uses-two-approaches-to-the-intersection-as-well}}{Elebeta.}
	}
\fi

\subsubsection{9}{U-Turn and Curbside Turn (“U-curb”)}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:u-turn-and-curbside-turn-u-curb}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 317-340: code points 1-6

Another alternative is possible by means of making a U-turn at a median break downstream of the crossing road, followed by a right turn at the crossing road (Figure 24.43).\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 319-320: code points 1-67

The U-turn and queue area may be accommodated at the curbside instead of in the median side, as shown in Figures 24.44, 24.45, and 24.46, where it accommodates cross-side-turn detoured flows from both the parallel and perpendicular streets: parallel doing U-turn then curbside, the perpendicular doing curbside then U-turn.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 322-325: code points 1-12

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		\fignote{43}{U-turns after crossing the intersection are an alternative to eliminate a cross-traffic-turn phase, but they require the flow to cross the intersection twice and require width for queueing downstream.\label{chapter:intersections-and-signal-control:figure:u-turns-after-crossing-the-intersection-are-an-alternative-to-eliminate-a-cross-traffic-turn-phase-but-they-require-the-flow-to-cross-the-intersection-twice-and-require-width-for-queueing-downstream}}{Elebeta.}
	}
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		\img{\hsize}{infrastructure/assets/cc2624c89b40541d3525edd6e989c635ab977393.png}
		\fignote{44}{Waiting area for a U-turn can be placed closer to the curb, instead of close to the median.\label{chapter:intersections-and-signal-control:figure:waiting-area-for-a-u-turn-can-be-placed-closer-to-the-curb-instead-of-close-to-the-median}}{Elebeta.}
	}
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		\img{\hsize}{infrastructure/assets/7ddc5404394eb15ddc8b3760004fae8be6b8ed1d.jpeg}
		\fignote{45}{Dongpu BRT station in Guangzhou, provides at-grade station access at both ends, combined with U-turns.\label{chapter:intersections-and-signal-control:figure:dongpu-brt-station-in-guangzhou-provides-at-grade-station-access-at-both-ends-combined-with-u-turns}}{ITDP with GMEDRI.}
	}
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		\fignote{46}{This intersection near Dongpu BRT Station in Guangzhou was previously a major traffic black spot—a location where traffic accidents often occurred—but now it works very smoothly for all modes, with a two-phase signal combined with U-turns and pedestrian crossings.\label{chapter:intersections-and-signal-control:figure:this-intersection-near-dongpu-brt-station-in-guangzhou-was-previously-a-major-traffic-black-spota-location-where-traffic-accidents-often-occurredbut-now-it-works-very-smoothly-for-all-modes-with-a-two-phase-signal-combined-with-u-turns-and-pedestrian-crossings}}{Karl Fjellstrom, ITDP.}
	}
\fi

\subsubsection{10}{Diverting Straight Flow: Parallel Street}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:diverting-straight-flow-parallel-street}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 342-352: code points 1-45

The use of the immediate parallel street in one way as an auxiliary street is an effective alternative for mixed traffic. Even a narrow two-way street transformed into a one-way street with parking prohibition can be a meaningful alternative for straight traffic and avoid the need for widening and expropriation. If applied both to BRT corridor and the corridor crossing, it can alleviate intersections. In São Paulo it is common that the “auxiliary” streets end up having higher throughput than the main corridors (Figure 24.47).\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 344-349: code points 1-7

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		\img{\hsize}{infrastructure/assets/01efff2d21369b729051c2915561445f2ccc20d4.png}
		\fignote{47}{Auxiliary street (left) has higher mixed-traffic capacity than the main corridor (right) in São Paulo.\label{chapter:intersections-and-signal-control:figure:auxiliary-street-left-has-higher-mixed-traffic-capacity-than-the-main-corridor-right-in-so-paulo}}{Google Maps.}
	}
\fi

\subsubsection{11}{Moving Across or Making a U-turn Away from the Intersection}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:shortening-and-eliminating-phases:subSubSection:moving-across-or-making-a-u-turn-away-from-the-intersection}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 354-365: code points 1-94

If the station location is seen as imperative, the intersection could be closed in order to avoid problems with the BRT system operation. Mixed traffic can be detoured around it. The examples for curbside and U-turn (Figures 24.48, 24.49, and 24.46) applied this detour to straight movements, too, even if the movements do not always surround the station.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 356-359: code points 1-45

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		\img{\hsize}{infrastructure/assets/360fa402eec3c9fd7188e40feb5e1e129babe418.png}
		\fignote{48}{Traffic is diverted past this TransOeste station in Rio de Janeiro before it is allowed to perform U-turns away from the station.\label{chapter:intersections-and-signal-control:figure:traffic-is-diverted-past-this-transoeste-station-in-rio-de-janeiro-before-it-is-allowed-to-perform-u-turns-away-from-the-station}}{Google Earth.}
	}
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		\img{\hsize}{infrastructure/assets/fbf436dc801ed6e96de9914663ccd19591a2e24e.jpeg}
		\fignote{49}{Dongpu BRT station in Guangzhou (see layout at Figure 24.45) provides at-grade station access at both ends, combined with mixed-traffic U-turns.\label{chapter:intersections-and-signal-control:figure:dongpu-brt-station-in-guangzhou-see-layout-at-figure-2445-provides-at-grade-station-access-at-both-ends-combined-with-mixed-traffic-u-turns}}{Karl Fjellstrom.}
	}
\fi

\subsection{3}{Creating Two-Phase Intersections}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:creating-two-phase-intersections}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 367-398: code points 1-31

Many of the detour options assume that an adjacent secondary-street system exists and has the capacity to absorb additional traffic caused by the proposed diversions. When they do not exist, widening one of the roads to accommodate U-turns and\slash{}or previous cross-traffic turns is usually a more feasible alternative. Deciding which detour alternatives apply to each flow requires a careful evaluation of both the demand intensity and fluctuations throughout the day in the intersection and surrounding streets, as well as the possibility of widening the approaches.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 369-374: code points 1-43

An infinite number of designs exist, including roundabouts and hamburger-shaped intersections and others that have yet to be created. \emphasis{The goal is to increase the proportion of green time given for the corridor direction}, which will result in a natural increase of capacity for traffic.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 376-378: code points 1-76

\emphasis{Alternatives that invert the way—that is, making a right-handed system in a location where a left-hand system is used or vice versa—should not be proposed} (in our experience, even if the flow is completely channeled and pedestrians and bicycle crossings are grade-separated, there should be safer alternatives). The common situation of a flowing busway amid congested mixed traffic is enough potential danger to deal with at the intersection. The importance of an enforcement policy to slow down BRT drivers in this situation cannot be stressed enough.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 380-385: code points 1-26

For mixed traffic in particular, measuring travel time alone is not the right metric to evaluate and monitor the quality of a solution. It is very likely (and frustrating) that one will see congestion returning after implementation on a major intersection. When that happens, one must remember that, besides accommodating rapid public transport, there are capacity gains for mixed traffic. Congestion seems to be the only general traffic deterrent, so if a good design will enable more people to cross the intersection by car, then that might mean that either travel times or congestion were eliminated somewhere else or that more people are willing to come to that area and benefit from the activities that part of the city has to offer.\par
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When the adjacent land use is primarily residential, there is likely to be considerable resistance to the above proposals. One should keep in mind that this is a normal pressure of city growth (historically, cities grew out of road intersections), and a broader perspective to regulate the use of land may need to be brought into the project.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 395-398: code points 1-31

\subsection{4}{Comparison Examples}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:comparison-examples}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 400-765: code points 1-0

For an initial general analysis of the possible configuration, we graphically present the cycle time as a function of required relative green times for vehicular phases (Figure 24.50). We consider both the situation where a pedestrian phase is required and not. When required, we assume the pedestrian phase will need 10 seconds plus 4 seconds of clearance, which is the time needed for crossing three lanes. The clearance (or lost time) for each phase is 4 seconds as well.\par
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		\fignote{50}{When demand requirements get too close to traffic signal capacity (overall intersection capacity) required cycles get too long very quickly.\label{chapter:intersections-and-signal-control:figure:when-demand-requirements-get-too-close-to-traffic-signal-capacity-overall-intersection-capacity-required-cycles-get-too-long-very-quickly}}{Elebeta.}
	}
\fi

By observing the chart, it is clear that when the pedestrian crossing phase is present, at the moment green times are required to be 75 percent, the intersection is near to collapse. This threshold is between 80 and 85 percent if no pedestrian phase is required.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 411-413: code points 1-53

The chart also shows that increasing cycles beyond 120 seconds is not efficient in any situation. In the best case (4 vehicular phases plus pedestrian phase), increasing it to 150 seconds (+25 percent) results in a 5 percent increase in capacity, and raising it to 300 seconds will add 10 percent more capacity. Such a desperate measure will of course prevent queueing formation during the peak hour and that certainly reduces travel times, but other measures can be much more efficient.\par
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If the BRT users are not to be stuck in traffic, and delay is computed equally to the car users, then it is very likely that raising cycle times above 120 seconds will result in overall time losses. Furthermore, if curbside turns are detoured or refuge islands are used as discussed in Section 24.9, then a proper set of two-phase signals will not require a pedestrian-only phase. In such a situation cycle times above 60 seconds are likely to be useless, and cycle times above 90 seconds are certainly not justifiable. As seen in Section 24.3, short cycles greatly reduce the chances of spillbacks on the busway, hindering stations.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 421-427: code points 1-9

For a comparison of different configuration impacts, we will assume a very symmetrical four-leg intersection, where the flow from each origin is equal and the left and right turns each represent 25 percent of traffic movements, straight represents 50 percent, and there is no U-turn demand. We will also assume a three-lane approach for mixed traffic in each leg as previous figures in this section show, with saturation capacity flow rate of 1,800 pcu\slash{}hour. When required, only one lane is used for cross-traffic turns per approach. We maintain the same assumptions to draw the chart regarding clearance times (4 seconds per phase change) and pedestrian phases (14 seconds per phase when phase required, and we assume it is not required in two-phase intersections).\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 429-436: code points 1-25

\subsubsection{1}{Typical Four-Phase Intersection}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:comparison-examples:subSubSection:typical-four-phase-intersection}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 438-530: code points 1-23

For comparing the four-phase intersection, we will fix cycle times at 120 seconds (2 minutes) and evaluate the effect of green time for the straight flow in one of the directions considering detouring curbside turns for each direction (two ways), and we will divide the overall capacity of the intersection by the number of lanes approaching it (NLanes in our example is 12 and results are in table 24.3).\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 440-443: code points 1-91

\tabletitle{3}{Four-Phase Capacity Examples}
\label{chapter:intersections-and-signal-control:table:four-phase-capacity-examples}
\halign to 30\tablemodule{%
	\vtop{\sffamily\footnotesize\noindent\hsize=5\tablemodule#}\hbox to 0.5\tablemodule{}&
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	\hbox to 0.5\tablemodule{}\vtop{\sffamily\footnotesize\noindent\hsize=5\tablemodule#}\cr
	\color{gray75}\bfseries Cycle Time (seconds)& \color{gray75}\bfseries Phases& \color{gray75}\bfseries Direction 1 Curb-Side-Turn& \color{gray75}\bfseries Direction 2 Curb-Side-Turn& \color{gray75}\bfseries Direction 1 Straight Movement Green Time (seconds)& \color{gray75}\bfseries Average Lane Capacity (pcu\slash{}hour) \cr
	\noalign{\vskip 1mm} \hline \noalign{\vskip 2mm} 
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% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 445-509: code points 1-9

Under the proposed scenario, a “standard-four-phase” signal has 90 seconds to distribute among the phases (30 out of 120 seconds are for pedestrian plus clearance times of phases changes), so this means 22.5 seconds per phase (rounded to 23 in the table) in the symmetrical situations. By detouring curbside turns to one side only (letting only 75 percent of demand be served), 3 seconds can be removed from the lesser demanded phases and passed to the other two (19 and 26 seconds); the capacity of each lane of each approach is always equal, meaning that 4,050 vehicles overall could pass through the intersection in one hour in the 12 lanes (= 338 x 12).\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 511-517: code points 1-41

In comparison, the “symmetrical phases,” which do not require a pedestrian phase, can distribute 104 seconds among the phases, and it ends up being 31 seconds for the straight traffic and 21 seconds for the cross-traffic turn (this last information is not on the table but is deductible). If lanes could be used in fractions, then allocating three-quarters of a lane to cross-traffic turns would lead to a balanced situation of 26 seconds of green time for each phase, which is the case when both curbside turns are removed from the intersection.\par
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On the balanced situation, when the symmetrical phases have the lowest capacity, they still have the same capacity as the standard phases, the higher throughput being a consequence only of the absence of the pedestrian-only phase. As a general rule, symmetrical phases are more efficient than standard phases. Mixed-phase results are not shown, but they are in between, closer to standard phases as they require pedestrian phases, too.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 526-530: code points 1-23

\subsubsection{2}{Reducing Number of Phases Effects}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:restricting-general-traffic-turning-movements:subSection:comparison-examples:subSubSection:reducing-number-of-phases-effects}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 532-765: code points 1-0

The previous discussion about four-phase intersections lay the groundwork for not considering the “mixed-four-phase” alternative in the following examples. This is also a reason why there is no need to present a previous cross-traffic turn, interlacing the BRT lane and mixed traffic (Figure 24.82), which shifts mixed traffic to the median side into a position that allows a standard four-phase intersection to work where no other alternative is possible; \emphasis{the symmetrical-phases signal works better}.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 534-538: code points 1-70

To compare the effects of alternative schemes for phase reduction, we will consider a 90-second cycle time without a pedestrian-only phase but with an additional BRT lane in one direction on the median side (also as shown on most figures in this section). The resulting green time for the BRT for each alternative is presented beside the intersection capacity of mixed traffic in Table 24.4, where:\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 540-543: code points 1-84

\begin{itemize}
\item \highlight{Average lane capacity:} the average of the mixed-traffic lanes capacity that would be measured at the stop lines approaching the main intersection;% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 545-547: code points 1-0
\item \highlight{Overall intersection capacity per lane:} in certain configurations, some vehicles pass through two stop lines in order to execute their turning movements, and this measure would be similar to average lane capacity above, except that it does not count the second passage of the same vehicle.% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 547-550: code points 1-0
\item \highlight{Total throughput with auxiliary intersections per lane at intersection: }this adds the flows that were completely diverted away from the main intersection (curbside-turn detour and previous cross-traffic-turn detour) as if they were effectively passing through the intersection. By bringing the value to the number of lanes of the intersection, this presents a practical estimate of how much the capacity of the main intersection can be pushed to benefit from using the auxiliary ones.% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 550-554: code points 1-93
\end{itemize}
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 545-554: code points 1-93

\tabletitle{4}{Increasing Capacity Examples}
\label{chapter:intersections-and-signal-control:table:increasing-capacity-examples}
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	\color{gray75}\bfseries \highlight{Option}& \color{gray75}\bfseries \highlight{Cycle Time (seconds)}& \color{gray75}\bfseries \highlight{Phases}& \color{gray75}\bfseries \highlight{BRT Direction Curb-Side-Turn Detour}& \color{gray75}\bfseries \highlight{BRT Direction Cross-Traffic-Turn Detour}& \color{gray75}\bfseries \highlight{Perpendicular Direction Curb-Side-Turn Detour}& \color{gray75}\bfseries \highlight{Perpendicular Direction Cross-Traffic-Turn Detour}& \color{gray75}\bfseries \highlight{Figure}& \color{gray75}\bfseries \highlight{BRT Green Time (seconds)}& \color{gray75}\bfseries \highlight{Average Lane Capacity (pcu\slash{}hour)}& \color{gray75}\bfseries \highlight{Overall Intersection Capacity per Lane (pcu\slash{}lane)}& \color{gray75}\bfseries \highlight{Total Throughput with Auxiliary Intersections per Lane at Intersection} \cr
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	\color{gray50}Fig. 24.35&
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	\color{gray50}Fig 24.37&
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	\noalign{\vskip 2mm 
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	\color{gray50}“clove like”&
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	\noalign{\vskip 2mm 
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	\color{gray50}90&
	\color{gray50}2&
	\color{gray50}-&
	\color{gray50}u-curb&
	\color{gray50}-&
	\color{gray50}curb-u&
	\color{gray50}Figs. 24.43 and 24.44&
	\color{gray50}49&
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	\color{gray50}655&
	\color{gray50}655\cr
	\noalign{\vskip 2mm 
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% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 556-739: code points 1-9

In our scenario, detouring all curbside turns away implies that 25 percent of cars are not using the approaching lanes to the intersection, and 75 percent of them are. So for each vehicle at the intersection, there is an additional third outside, which means a 33 percent increase in “intersection capacity.”\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 741-743: code points 1-99

In comparison with the four-phase (symmetrical) signal, even the three-phase signal implies a considerable increase of green time for the BRT. Reducing 4 phases to 3 leads to a 25 percent increase for the capacity at the intersection (and 50 percent considering auxiliary intersections) with satisfactory relative green time near 50 percent. Meanwhile, from the point of view of mixed traffic throughput, the reduction from 4 to 2 phases in the worst cases (U-turn alternatives and only loops: J, L, and M), an 80 percent increase for the throughput occurs at the intersection, and in the best alternative (option I), there is a 107 percent increase at the intersection while green times are in the same range (except for alternative M, which uses U-turns at the perpendicular street). Implementing a two-phase signal is clearly the best thing to do.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 745-753: code points 1-12

When traffic signals are balanced to serve the demand with a two-phase traffic signal, it will result in the capacity of about 820 pcu\slash{}hour. For this situation a cycle of 90 seconds with 4 seconds of clearance is typically used. Additionally, if the flow looking to turn is placed on the (curbside) parallel streets in both directions (option I), then one can reach an equivalent of 1,092 pcu\slash{}hour. This results in 60 percent of uninterrupted lane capacity as an average for two directions, which is likely to represent 75 percent of the average of the best grade-separated solution and be better than many graded-separated solutions (see Section: 24.10.3 Restricting Turning Movements Together with Grade Separation). Plus, this is 320 percent of the average capacity of a standard four-phase intersection. Clearly, the consideration of the detour alternatives to reduce signal phases can do a lot to increase green time for the corridor as well as capacity for mixed traffic.\par
% @ guide/24-intersections_and_signal_control/245-restricting-general-traffic-turning-movements.src: lines 755-765: code points 1-0

\section{6}{Allowing BRT Turns}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:allowing-brt-turns}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 1-263: code points 1-7

\quotation{An Englishman, even if he is alone, forms an orderly queue of one.}{George Mikes, writer, 1912-1987}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 3-4: code points 1-33

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		\img{\hsize}{infrastructure/assets/f9009374d0d3e50e80065728ddc480203437fd88.jpeg}
		\fignote{51}{A tunnel is used to connect two intersecting corridors in Bogotá. Even if the connection is good, walking times could be reduced if routes shifted from one corridor to another.\label{chapter:intersections-and-signal-control:figure:a-tunnel-is-used-to-connect-two-intersecting-corridors-in-bogot-even-if-the-connection-is-good-walking-times-could-be-reduced-if-routes-shifted-from-one-corridor-to-another}}{Lloyd Wright.}
	}
\fi

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		\fignote{52}{Separated-grade walking connections provide safety but also are limited in convenience. Walking transfers can cause physical hardship.\label{chapter:intersections-and-signal-control:figure:separated-grade-walking-connections-provide-safety-but-also-are-limited-in-convenience-walking-transfers-can-cause-physical-hardship}}{Lloyd Wright.}
	}
\fi

While service plan simplification and organization may, to an extent, minimize turning movements for BRT vehicles in the busway, by concentrating service access to the corridor in a few intersections, turning is necessary and desired where it best serves the demand (in opposition to allowing it where it is convenient by geometry). By planning BRT routes that change between corridors (i.e., with turns), easy platform transfers for the customers are made possible, better, or not even necessary for most users. Thus, turning movements by BRT vehicles should be an integral part of designing an effective overall route structure. As the BRT system expands and provides an increasingly dense network of lines, the connections between these lines become more complex. While a BRT system expands, a growing number of trunk corridors crossing each other is expected.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 12-20: code points 1-23

The costs of not allowing turning movements by BRT vehicles are quite evident, especially in terms of customer convenience. Quito’s three BRT corridors (Trolé, Ecovía, and Metrobus-Q) all operate as independent corridors, despite each intersecting one another at several points in the city. At one of the critical intersections between two intersecting BRT corridors in Bogotá (Caracas and Jimenez), customers must transfer by negotiating passages along stairs and an underground tunnel (Figures 24.51 and 24.52). In both these examples, allowing turning movements by the BRT vehicles could have permitted simpler and more convenient platform transfers for the customer. Furthermore, constructing connecting pedestrian tunnels can add much to the overall infrastructure costs of the system. This is copying the bad parts of rail systems. In the Bogotá situation, customer convenience has been significantly increased by allowing turn movements and direct transfers between the Caracas and Jimenez corridors.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 22-31: code points 1-78

There are several solutions to allow BRT vehicle turning that avoid consuming much of an intersection’s capacity—mostly needed for cars in the intersection—and the appropriate solutions will depend on the available budget and right-of-way, the number of vehicles in the BRT system and their turning volumes, and the level of mixed traffic and its turning volumes. The optimal solution will be location-specific and each intersection must be evaluated and optimized separately. Here are common options for busway turning movements:\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 33-38: code points 1-18

\begin{enumerate}
\item Dedicated turning lanes and additional signal phases for BRT vehicles;% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 40-41: code points 1-0
\item BRT vehicles operating in mixed-traffic turning lanes;% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 41-42: code points 1-0
\item BRT turning movements prior to the intersection;% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 42-43: code points 1-0
\item Transform the crossing into a roundabout;% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 43-44: code points 1-0
\item Grade separation (discussed in Section 24.10).% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 44-44: code points 1-54
\end{enumerate}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 40-44: code points 1-54

\subsection{1}{Dedicated Turning Lanes and Additional Signal Phases for BRT Vehicles}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:allowing-brt-turns:subSection:dedicated-turning-lanes-and-additional-signal-phases-for-brt-vehicles}
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		\img{\hsize}{infrastructure/assets/28e83c49cf8e39a9188d37f3f01dc96fabdc9d45.jpeg}
		\fignote{53}{The green phase for a BRT vehicle entering the Val de Marne busway in Paris.\label{chapter:intersections-and-signal-control:figure:the-green-phase-for-a-brt-vehicle-entering-the-val-de-marne-busway-in-paris}}{National Bus Rapid Transit Institute (NBRTI).}
	}
\fi

A dedicated turning lane for BRT vehicles has the advantage of keeping the BRT vehicles in a controlled space at all times (see Figure 24.53). This arrangement may require an additional signal phase if there was no previous cross-traffic-turn phase. Otherwise, the dedicated turn would take place at the same time that the mixed traffic is allowed to turn left.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 51-54: code points 1-52

Possibly the greatest challenge to this configuration is finding the physical space to place the additional turning lane. The roadway would likely have to accommodate at least five lanes (Figure 24.54). If two lanes of mixed traffic in each direction are to be maintained for straight-car movements, then seven lanes of road space would be required.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 56-59: code points 1-38

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		\img{\hsize}{infrastructure/assets/4f5f990de9466698f4f2bde0fb04ec429d53d5f4.png}
		\fignote{54}{Configuration for a system with a fully dedicated BRT turning lane.\label{chapter:intersections-and-signal-control:figure:configuration-for-a-system-with-a-fully-dedicated-brt-turning-lane}}{ITDP.}
	}
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		\fignote{55}{In order to permit the BRT turning movements suggested in Figure 24.54, a three-phase traffic signal would be required.\label{chapter:intersections-and-signal-control:figure:in-order-to-permit-the-brt-turning-movements-suggested-in-figure-2454-a-three-phase-traffic-signal-would-be-required}}{ITDP.}
	}
\fi

The configuration suggested in Figure 24.54 would require a three-phase traffic signal, as indicated in Figure 24.55, and in the case of a median-station configuration it can provide full access to all route permutations without walking: a southbound vehicle turning east will give customers access to westbound routes via the platform transfer at the first station. In designing this option, one would choose the highest demand routes to receive the transfer-free routing.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 67-71: code points 1-59

In this scenario, one could technically also allow cross-traffic-turn movements for mixed-traffic vehicles for traffic from north and south, but even more additional lanes would be required. Ideally though, mixed traffic should be diverted as proposed in the previous section (Section 24.5: Restricting General Traffic Turning Movements) as the BRT cross-traffic turn phase will usually be very short (like the queue-jumping phase proposed in 24.5.2.1).\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 73-77: code points 1-28

If the turning BRT vehicle frequencies are low enough, the BRT-only short phase can accommodate both right and left turns from one direction as BRT vehicles’ drivers can negotiate entrance to the other corridor. That would avoid the need for two waiting lanes for turns.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 79-81: code points 1-68

The complexity of dedicated turning lanes obviously increases as turning options for both BRT vehicles and mixed-traffic vehicles increase. In the extreme case of permitting all BRT turning options and all mixed-traffic turning options, then a total of six traffic-signal phases would be required (Figure 24.56). This number of phases clearly holds disadvantages in terms of waiting times for both BRT and mixed-traffic movements and reduces the capacity of the intersection so drastically—besides requiring four lanes, four BRT lanes, and likely six for mixed traffic—that is very likely to not be feasible in a location where two important corridors cross each other.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 83-89: code points 1-47

\ifxetex
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		\fignote{56}{To permit a full range of both BRT and mixed-traffic turning movements, six signal phases would be required.\label{chapter:intersections-and-signal-control:figure:to-permit-a-full-range-of-both-brt-and-mixed-traffic-turning-movements-six-signal-phases-would-be-required}}{ITDP.}
	}
\fi

\subsection{2}{BRT Vehicles Operating in Mixed-Traffic Turning Lanes}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:allowing-brt-turns:subSection:brt-vehicles-operating-in-mixed-traffic-turning-lanes}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 94-143: code points 1-38

In this scenario, all turning BRT vehicles must leave the dedicated busway and enter mixed-traffic lanes. Thus, a cross-traffic-turning BRT vehicle will leave the busway and directly enter the cross-traffic-turn lane for cars. A curbside-turning BRT vehicle must leave the median-side busway and merge to the curbside of the street to reenter the median-side busway on the new corridor.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 96-99: code points 1-68

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		\fignote{57}{In Kunming, turning BRT vehicles leave the busway and enter a mixed-traffic lane to finalize the turning movement.\label{chapter:intersections-and-signal-control:figure:in-kunming-turning-brt-vehicles-leave-the-busway-and-enter-a-mixed-traffic-lane-to-finalize-the-turning-movement}}{ITDP.}
	}
\fi

This technique is the most common solution that has been used in many of the “open” BRT systems, such as in Kunming, China, and is being planned on several “direct services” BRT systems (Figure 24.57). If there is no physical separation of the busway, the merge with the mixed traffic can happen anywhere in the proceeding block. If there is physical separation, it must occur at the previous intersection, or a slip lane must be provided.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 104-108: code points 1-29

From a signal phase standpoint, this option is the easiest to implement, as it does not require changing the signal phase, and does not require any major new infrastructure. However, this option does present serious disadvantages in terms of congestion delay for the turning BRT vehicles, not to mention the assumed inefficiency of four stages to mixed traffic. Further, if the mixed-traffic congestion is heavy, the BRT vehicles attempting to turn may not be able to readily leave the busway, and thus can cause delays to all BRT vehicles, even those vehicles continuing in a straight routing. The BRT vehicle turning right has particular challenges since it must essentially cross all mixed-traffic lanes both before and after the intersection. Attempting these lane changes is particularly difficult if the system is using 18.5-meter articulated vehicles or 24-meter bi-articulated vehicles.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 110-118: code points 1-57

Any time BRT vehicles must leave an exclusive busway operation and enter mixed-traffic lanes the system loses a certain amount of psychological status with the customer. Mixed-traffic operation makes the system much more akin to a conventional bus system rather than a highly efficient public transport system.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 120-122: code points 1-99

\subsubsection{1}{Queue-Jump Signalization for BRT Vehicles (Pre-Signals)}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:allowing-brt-turns:subSection:brt-vehicles-operating-in-mixed-traffic-turning-lanes:subSubSection:queue-jump-signalization-for-brt-vehicles-pre-signals}
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\ifxetex
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		\img{\hsize}{infrastructure/assets/7b224cab71d758a3567465926675e5a9292a7d87.jpeg}
		\fignote{58}{While mixed-traffic vehicles are held for an extra ten seconds at the first traffic-signal stop, BRT vehicles are given a queue-jumping head start. Technically this counts as eight phases.\label{chapter:intersections-and-signal-control:figure:while-mixed-traffic-vehicles-are-held-for-an-extra-ten-seconds-at-the-first-traffic-signal-stop-brt-vehicles-are-given-a-queue-jumping-head-start-technically-this-counts-as-eight-phases}}{TCRP}
	}
\fi

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		\img{\hsize}{infrastructure/assets/e8f9053c612b6eb3bee2b4a7ed08f80fa43b277f.jpeg}
		\fignote{59}{Pre-signals for buses, holding normal vehicles in Cape Town, South Africa, work like a queue jump to a straight movement in a mixed-traffic section.\label{chapter:intersections-and-signal-control:figure:pre-signals-for-buses-holding-normal-vehicles-in-cape-town-south-africa-work-like-a-queue-jump-to-a-straight-movement-in-a-mixed-traffic-section}}{Bruce Sutherland.}
	}
\fi

A signal system can be utilized to give BRT vehicles a head start on turning movements prior to private-vehicle turning movements. In this case, a dual traffic signal is utilized for each direction of travel. One traffic signal is located at the intersection, and another traffic signal is located approximately 30 to 50 meters prior to the intersection. At the traffic signal prior to the intersection, the BRT vehicles on the busway would receive a green signal of approximately 10 seconds prior to the green signal for the mixed traffic (Figure 24.58). During this head start, the BRT vehicle would be able to exit the busway and cross to the other side of the street. This is the equivalent of having eight stages and, besides the same problems with congestion in mixed traffic, a BRT vehicle that arrives in the middle of the green phase will be blocked by cross-traffic-turning cars and block eventual vehicles behind it. Figure 24.59 shows an example of pre-signal without BRT turning; it is used as a way to allow mixed traffic turn cross-traffic when the roadway width is constrained.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 133-143: code points 1-38

\subsection{3}{BRT Turning Movements Prior to the Intersection}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:allowing-brt-turns:subSection:brt-turning-movements-prior-to-the-intersection}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 145-156: code points 1-76

To avoid having a special BRT turning phase in a main intersection, an alternative is to create a special bus-only turn (this is as good for left turns as for right) phase at an intersection before a major intersection where there is less crossing demand than in the main crossing corridor, or no demand at all (Figure 24.60). For a few blocks, the BRT vehicle will operate on secondary streets (in mixed traffic or in a dedicated lane) until it rejoins the busway. This option requires the availability of usable secondary streets and consideration regarding the placement and use of stations by turning routes (not to move it too far from the origin\slash{}destination of many trips on the other side of the main intersection).\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 147-153: code points 1-86

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/3c829546e2e1a4a2f81b14852dd8917920f9a340.png}
		\fignote{60}{In this scenario, the BRT turning movement is made prior to the main intersection. The BRT vehicle temporarily operates on the secondary road network.\label{chapter:intersections-and-signal-control:figure:in-this-scenario-the-brt-turning-movement-is-made-prior-to-the-main-intersection-the-brt-vehicle-temporarily-operates-on-the-secondary-road-network}}{ITDP.}
	}
\fi

\subsection{4}{Convert Cross into a Roundabout}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:allowing-brt-turns:subSection:convert-cross-into-a-roundabout}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 158-263: code points 1-7

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/3fdfd776b32d29d28f7dc7ca389a23cc8c1e6e96.png}
		\fignote{61}{In this scenario, the intersection is converted to a roundabout with vehicle queuing areas at points “A,” “B,” “C,” and “D.” The BRT vehicles enter mixed traffic just before the intersection and move through the intersection with a two-phase signal.\label{chapter:intersections-and-signal-control:figure:in-this-scenario-the-intersection-is-converted-to-a-roundabout-with-vehicle-queuing-areas-at-points-a-b-c-and-d-the-brt-vehicles-enter-mixed-traffic-just-before-the-intersection-and-move-through-the-intersection-with-a-two-phase-signal}}{ITDP}
	}
\fi

If two crossing corridors happen to be two broad highways, enough right-of-way may be available to convert a standard four-phase intersection into a two-phase signalized roundabout. This is a clever alternative that should be remembered, as in many developing-nation cities, such right-of-way is available but underutilized.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 164-166: code points 1-113

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/4b2b84ade563b374128088bfcfbc807567ff799c.png}
		\fignote{62}{Vehicle movements for signal phase 1 in a cross converted into a roundabout.\label{chapter:intersections-and-signal-control:figure:vehicle-movements-for-signal-phase-1-in-a-cross-converted-into-a-roundabout}}{ITDP.}
	}
\fi

The exclusive BRT busway terminates approximately 50 meters prior to the intersection with the BRT vehicles entering mixed traffic at that point. This approach essentially turns the junction into a grid of one-way streets. It requires a fairly large amount of right-of-way at the junction.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 170-172: code points 1-86

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/395cf185145b09f518d8882288a83de75eaf028f.png}
		\fignote{63}{Vehicle movements for signal phase 2 in a cross converted into roundabout.\label{chapter:intersections-and-signal-control:figure:vehicle-movements-for-signal-phase-2-in-a-cross-converted-into-roundabout}}{ITDP.}
	}
\fi

Figure 24.61 indicates how the junction between two major boulevards can be turned into a two-phase traffic circle by creating a kind of mini-grid of one-way streets. At low traffic volumes, the BRT buses enter mixed traffic prior to the intersection. A series of queuing areas (marked as “A,” “B,” “C,” and “D” in the figure) help stage vehicle flows through the roundabout. These areas are referred to as “waiting boxes.”\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 176-180: code points 1-7

Figure 24.62 outlines the vehicle movements for the first signal phase for this roundabout conversion. This example is given from the perspective of a British-style road configuration. All eastbound BRT vehicles and mixed-traffic vehicles that are making right-hand turns would pass through the intersection and queue in area “C” at a traffic light. All east- and westbound traffic can proceed straight. All vehicles making left-hand turns can proceed. All westbound traffic would pass through the intersection and queue in area “B.”\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 183-188: code points 1-4

In the second signal phase, all northbound and southbound traffic can proceed straight, all left-hand turns can proceed, and all right turning traffic would queue in areas “A” and “D” (Figure 24.63).\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 191-192: code points 1-97

This solution will work up to the point where the amount of space in areas “A,” “B,” “C,” and “D” is sufficient to accommodate all the turning traffic. The required and available space are discussed in Box 24.2.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 194-196: code points 1-9

Opposite of the rule to increase capacity, the cycle on a signalized roundabout of this type should be short, so the queueing box can handle volumes (manual operators must be very careful when handling these intersections, keeping an eye on the queueing boxes to decide when to alternate to the next phase). Other alternatives of busways through roundabouts are discussed in the next section.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 198-201: code points 1-84

\beginbox{2}{Required and available space for queueing boxes:}
\label{chapter:intersections-and-signal-control:box:required-and-available-space-for-queueing-boxes}
For the purpose of evaluating queueing space, we consider that:\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 205-205: code points 1-63

\begin{itemize}
\item The amount of road space that a passenger car practically uses is 15 square meters; this includes some distance kept between vehicles to separate them from each other when queueing at the traffic light ($ \text{Area}_\text{pcu} = 15 m^2$);% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 207-210: code points 1-0
\item The amount of road space needed for a 12 meter-bus to queue is 30 square meters, therefore its equivalence factor is 2.0, i.e., one 12 meter-bus uses twice the space a pcu;% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 210-212: code points 1-0
\item An articulated BRT vehicle has an equivalent factor of 3.5 pcu;% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 212-212: code points 1-69
\end{itemize}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 207-212: code points 1-69

The available area capacity and the required area (or demanded area) to transform a cross into a roundabout are:\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 214-215: code points 1-4

Eq. 24.24\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 217-217: code points 1-9

$ \text{Available Capacity}_\text{queue box} = {\text{Area}_\text{wait-box} \over \text{Area}_\text{pcu} } $\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 219-219: code points 1-110

Where:\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 221-222: code points 1-0

\begin{itemize}
\item $ \text{AvailableCapacity}_\text{queue box} $: Number of cars that fit in wait box (in pcu);% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 222-223: code points 1-0
\item $ \text{Area}_\text{wait box}$: Amount of space in the wait box (either "A", "B", "C" or "D" in Figure 24.61);% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 223-224: code points 1-0
\item $ \text{Area}_\text{pcu} $: Amount of road space a passenger-car uses 15 m\textsuperscript{2} (it should be expressed in the same unit of $ \text{Area}_\text{wait box} $).% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 224-225: code points 1-38
\end{itemize}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 222-225: code points 1-38

Eq. 24.25\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 227-227: code points 1-9

$ \text{RequiredCapacity}_\text{wait box} = \text{Flow}_\text{left turn} * \text{Time}_\text{cycle} $\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 229-229: code points 1-103

Where:\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 231-232: code points 1-0

\begin{itemize}
\item $ \text{RequiredCapacity}_\text{wait-box} $: Number of cars that need to fit in wait box (in the same unit the numerator of the measure described below, normally pcu);% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 232-234: code points 1-0
\item $ \text{Flow}_\text{left turn} $: Number of vehicles that turn left during the peak (normally expressed in pcu\slash{}hour, see basic concepts of this chapter);% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 234-236: code points 1-0
\item $ \text{Time}_\text{cycle} $: Time duration of a complete traffic light cycle during the peak (normally expressed in seconds, so here the same unit of the flow above needs to be converted, dividing the value by 3,600).% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 236-237: code points 1-101
\end{itemize}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 232-237: code points 1-101

In order for the configuration to function, the available space capacity must be equal or greater than the required capacity.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 239-240: code points 1-22

\emphasis{Example}\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 242-242: code points 1-9

The following scenario provides an example of calculating the required and available capacity of the proposed roundabout queuing space:\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 244-246: code points 1-0

\begin{itemize}
\item Turning movement = 540 pcu\slash{}hour = 0.15 pcu\slash{}sec;% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 246-247: code points 1-0
\item Cycle time = 90 sec.% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 247-247: code points 1-26
\end{itemize}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 246-247: code points 1-26

\highlight{Required capacity = 0.15 * 90 = 13.5 pcu}\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 249-250: code points 1-0

\begin{itemize}
\item Unitary pcu space = 3 m * 5 m = 15 m\textsuperscript{2};% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 250-251: code points 1-0
\item Length = 30 m;% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 251-252: code points 1-0
\item Width = 12 m.% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 252-252: code points 1-19
\end{itemize}
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 250-252: code points 1-19

\highlight{Available capacity = (30 m * 12 m) \slash{} (15 m\textsuperscript{2}\slash{}pcu) = 24 pcu}\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 254-254: code points 1-76

In this case, the available capacity is greater than the required capacity (24 pcu ≥ 13.5 pcu), so the proposed roundabout conversion could function.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 256-257: code points 1-50

Considering the Figure 23.61, when the number of mixed traffic vehicles and BRT vehicles rises to the point that areas “A,” “B,” “C,” and “D” are too small to accommodate them all, turns should be restricted for mixed traffic but not for BRT vehicles. Effectively, the queuing areas “A,” “B,” “C,” and “D” would be reserved for BRT vehicles.\par
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 259-263: code points 1-0

\endbox
% @ guide/24-intersections_and_signal_control/246-allowing-brt-turns.src: lines 203-263: code points 1-7

\section{7}{Merging with Mixed Traffic in Narrow Sections}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:merging-with-mixed-traffic-in-narrow-sections}
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 1-57: code points 1-0

\quotation{Well, you would have to say what is the criteria to determine the success of any merger? It would have to be that the companies are stronger financially, that they took market share, and they are on a very steady footing in terms of their performance.}{Kevin Rollins, businessman and philanthropist, 1952-}
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 3-4: code points 1-54

Sometimes a BRT system must pass through a narrow stretch of road that is impossible to widen. Such areas may include bridges, tunnels, city gates, or flyovers. As shown below, having the BRT running with mixed traffic only in this narrow section may not be too harmful for the public transport system if appropriate measures are taken.\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 6-9: code points 1-19

This situation can be seen as an intersection (a form of a bottleneck) as there is conflict for using the same space. Usually the heaviest congestion occurs not on the narrow link but just before it, forming a large queue just to enter onto the bottleneck point. When the facility itself is not congested, only the approach to the facility, a traffic signal is generally not needed, and it may be better to end the exclusive busway just a short distance before the bottleneck. The distance should be sufficient only to allow a convenient distance for merging (40 to 80 meters). This curtailment of the busway will allow BRT buses to pass through most of the congestion point without provoking any reduction of mixed traffic capacity at the critical section (Figure 24.64).\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 11-18: code points 1-48

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/8520ac801567f949f481a62bb0b90a66680bc4ac.png}
		\fignote{64}{In the case of a severe bottleneck point, it may be best to terminate the exclusivity of the busway prior to reaching the bottleneck.\label{chapter:intersections-and-signal-control:figure:in-the-case-of-a-severe-bottleneck-point-it-may-be-best-to-terminate-the-exclusivity-of-the-busway-prior-to-reaching-the-bottleneck}}{ITDP}
	}
\fi

If the critical link is an approach to a signalized intersection (Figure 24.65), then BRT should be given signal priority (active priority if BRT has lower frequency, passive priority in all other cycles), and the head start in the green phase ($ _\text{Theadstart}$) should be given by:\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 23-25: code points 1-83

Eq. 24.26\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 27-27: code points 1-9

$ T_\text{headstart} = {\text{Dist}_\text{stop to narrow section} \over \text{StartSpeed}_\text{BRT}} $\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 29-29: code points 1-105

Where:\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 31-32: code points 1-0

\begin{itemize}
\item $ T_\text{headstart} $: Time of head start in the green phase;% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 32-33: code points 1-0
\item $ \text{Dist}_\text{stop to narrow section} $: Distance between the stop line of the signal preceding the narrow section;% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 33-34: code points 1-0
\item $ \text{StartSpeed}_\text{BRT} $: An average head start speed that the BRT vehicle needs as an advantage over mixed traffic to reach the section first. We suggest 3 m\slash{}s (\~ 11 km\slash{}hour). Using meters and seconds the equation becomes:% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 34-35: code points 1-107
\end{itemize}
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 32-35: code points 1-107

$ T_\text{headstart}[seconds] = {\text{Dist}_\text{stop-to-narrow-section}[meters] \over 3  } $\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 37-37: code points 1-97

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/be05d070a5cd210293f2d71d5d91537cbef3f92a.png}
		\fignote{65}{In the case of a severe bottleneck approach with traffic lights, signal priority is to be given to BRT (passive or active).\label{chapter:intersections-and-signal-control:figure:in-the-case-of-a-severe-bottleneck-approach-with-traffic-lights-signal-priority-is-to-be-given-to-brt-passive-or-active}}{ITDP}
	}
\fi

The example given in Figure 24.65 essentially acts as a queue-jumping mechanism in which the BRT vehicles are given an advantage through a bottleneck point.\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 42-43: code points 1-50

The head start, however, is useless if the facility itself also becomes congested. If there is a risk that the bottleneck facility itself may become congested (due to mixed traffic spillback of conflicts ahead of the narrow section), active signal priority based on the detection of mixed traffic should be used.\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 45-48: code points 1-5

The signal before the section would work normally (or if a signal did not exist one would be created and flash yellow) until traffic detectors note that the narrow link has become congested (at its most downstream portion). At that point, the signal would be activated, and a red light would be given to mixed traffic until the narrow section clears. The use of such a traffic signal will help to avoid congestion inside the busway. Instead the delay is transferred to the mixed traffic in the previous link, resulting in improved velocity for BRT vehicles at the narrow link. For tunnels, this approach has the extra advantage of avoiding idling vehicles within heavily polluted conditions.\par
% @ guide/24-intersections_and_signal_control/247-merging-with-mixed-traffic-in-narrow-sections.src: lines 50-57: code points 1-0

\section{8}{BRT Lanes at Roundabouts}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:brt-lanes-at-roundabouts}
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 1-65: code points 1-14

\quotation{So many roads. So many detours. So many choices. So many mistakes.}{Carrie Bradshaw (as played by Sarah Jessica Parker), “Coulda, Woulda, Shoulda,” Sex and the City, 2001}
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 3-4: code points 1-104

Intersections with roundabouts can create considerable uncertainty for the busway system. If the BRT vehicle must cross several lanes of mixed traffic within a heavily congested roundabout, the BRT vehicle may be hindered from proceeding.\par
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 6-8: code points 1-32

However, there are some solutions to the difficulties posed by roundabouts. There are at least five distinct possibilities for accommodating BRT systems through a roundabout:\par
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 10-11: code points 1-74

\begin{enumerate}
\item Mixed traffic operation;% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 13-14: code points 1-0
\item Mixed traffic operation with signalized waiting areas;% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 14-15: code points 1-0
\item Exclusive lane along the inside of a roundabout;% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 15-16: code points 1-0
\item Exclusive busway through the middle of the roundabout;% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 16-17: code points 1-0
\item Grade separation.% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 17-17: code points 1-25
\end{enumerate}
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 13-17: code points 1-25

\subsection{1}{Mixed-Traffic Operations:}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:brt-lanes-at-roundabouts:subSection:mixed-traffic-operations}
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 19-25: code points 1-70

If mixed traffic and BRT system volumes are not particularly heavy and\slash{}or if the roundabout has no traffic lights, then simply allowing the BRT vehicles to enter mixed traffic may be an effective and simple solution. In such cases, the BRT vehicle will leave the dedicated busway upon entering the roundabout, which may be either controlled through a traffic signal (eventually a new traffic signal and\slash{}or activated by the vehicle approach) or left to operate on a yield priority basis.\par
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 21-25: code points 1-70

\subsection{2}{Mixed-Traffic Operation with Signalized Waiting Area:}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:brt-lanes-at-roundabouts:subSection:mixed-traffic-operation-with-signalized-waiting-area}
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 27-32: code points 1-37

In this situation, a standard intersection is converted to a roundabout with signalized control as described in the end of Section 24.6.4. When a standard intersection has reached its saturation point, then BRT-only waiting areas should be created and private vehicles must be accommodated in a variety of turning options already discussed.\par
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 29-32: code points 1-37

\subsection{3}{Exclusive Lane along the Inside of a Roundabout:}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:brt-lanes-at-roundabouts:subSection:exclusive-lane-along-the-inside-of-a-roundabout}
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 34-44: code points 1-48

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/153300bb40d694e386f2be3b05e5b60a3b40dbb0.png}
		\fignote{66}{TransJakarta’s first corridor passes along the inside of several roundabouts.\label{chapter:intersections-and-signal-control:figure:transjakartas-first-corridor-passes-along-the-inside-of-several-roundabouts}}{Google Earth.}
	}
\fi

In cases where BRT and mixed-traffic volumes dictate that some priority must be retained for the BRT vehicles, then making the inside lanes of the roundabout exclusive to BRT can be an effective option (Figure 24.66). In this case, the BRT vehicles can access the exclusive roundabout lanes either by crossing mixed-traffic lanes or by receiving priority signalization. Likewise, to exit the roundabout and re-enter the principal busway, the BRT vehicle must cross mixed-traffic lanes. As with the entry to the roundabout, the BRT vehicles can either maneuver across mixed traffic to exit the roundabout or another set of traffic signals can be used to facilitate the operation.\par
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 38-44: code points 1-48

\subsection{4}{Exclusive Busway through the Middle of a Roundabout:}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:brt-lanes-at-roundabouts:subSection:exclusive-busway-through-the-middle-of-a-roundabout}
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 46-60: code points 1-125

Depending on the physical contents of the roundabout, a dedicated lane could be constructed through the center of the roundabout. In this case, the busway is built straight through the roundabout, while mixed traffic continues to circulate around it. Quito’s Ecovía line provides an example of this technique (Figure 24.67). Likewise, the Cali, Colombia, system also makes use of this approach (Figure 24.68). The ability to construct a dedicated lane through the center of the roundabout will only be feasible when the center area of the roundabout does not host a fountain, sculpture, or other permanent piece of urban infrastructure. The construction of the BRT system should not involve the loss of any items of cultural identity. In this design, a traffic signal controls movement through the roundabout.\par
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 48-55: code points 1-96

\ifxetex
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		\img{\hsize}{infrastructure/assets/607f9f173f7bfdf800627f8448486392fcc5139e.jpeg}
		\fignote{67}{Quito’s Ecovía line cuts directly through a roundabout.\label{chapter:intersections-and-signal-control:figure:quitos-ecova-line-cuts-directly-through-a-roundabout}}{Lloyd Wright.}
	}
\fi

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		\img{\hsize}{infrastructure/assets/c9c9a6c9e228e87311f03f54a602d51f4f3befb6.jpeg}
		\fignote{68}{In Cali, the busway also passes through the center of the roundabout area.\label{chapter:intersections-and-signal-control:figure:in-cali-the-busway-also-passes-through-the-center-of-the-roundabout-area}}{Metrocali.}
	}
\fi

\subsection{5}{Grade separation}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:brt-lanes-at-roundabouts:subSection:grade-separation}
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 62-65: code points 1-14

This alternative is discussed at the Section 24.10, after other aspects of grade-separated solutions are presented.\par
% @ guide/24-intersections_and_signal_control/248-brt-lanes-at-roundabouts.src: lines 64-65: code points 1-14

\section{9}{Integrating Pedestrian and Cyclist Movements}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:integrating-pedestrian-and-cyclist-movements}
% @ guide/24-intersections_and_signal_control/249-integrating-pedestrian-and-cyclist-movements.src: lines 1-67: code points 1-41

\quotation{The way I see it, I can either cross the street, or I can keep waiting for another few years of green lights to go by.}{Camryn Manheim, actress, 1961-}
% @ guide/24-intersections_and_signal_control/249-integrating-pedestrian-and-cyclist-movements.src: lines 3-4: code points 1-32

A highly efficient intersection for mixed traffic and BRT vehicles may not be user-friendly to other street users, especially vulnerable users such as pedestrians and cyclists. Further, the entire viability of the BRT system can be undermined if the surrounding pedestrian environment is not amenable to attracting customers to the BRT station. This section examines design options that not only are conducive to effective vehicle movements at intersections but also options that successfully accommodate pedestrian and cyclist movements.\par
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		\fignote{69}{In a standard two-phase traffic signal, pedestrians are potentially at risk during both phases.\label{chapter:intersections-and-signal-control:figure:in-a-standard-two-phase-traffic-signal-pedestrians-are-potentially-at-risk-during-both-phases}}{ITDP.}
	}
\fi

A standard two-phase traffic signal configuration does not offer any exclusive movements for pedestrians (Figure 24.69). The pedestrian is blocked by crossing or turning traffic in either phase. In such circumstances, the pedestrian must seek a discernible break in the traffic and make a quick crossing. Such conditions may put pedestrians at considerable risk.\par
% @ guide/24-intersections_and_signal_control/249-integrating-pedestrian-and-cyclist-movements.src: lines 16-19: code points 1-41

The lack of safe pedestrian options can also be the case for three- and four-phase intersections, depending on the configuration. If intersections are designed to slow turning vehicles and if turning vehicle volumes are not that high, the problem may not be serious, and it is eventually better for pedestrians that do not have to wait a whole cycle to cross. However, if turning volumes are high or intersections allow high speed curbside turns, bicyclists and pedestrians going straight will have problems crossing the road.\par
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The normal solution to this problem is the creation of a pedestrian refuge island between the curbside turn slip lane and the intersection while not allowing curbside turns during the red signal phase (Figure 24.70). Pedestrians can generally cross to this pedestrian refuge island during the red phase and then cross when the light turns green. Another possible solution for this is a short “leading pedestrian interval” that allows pedestrians to cross in front of the curbside turning vehicles prior to the change of the signal to green. This option still requires preventing curbside turns on the red signal but mitigates the need for the pedestrian refuge island. More discussion on safe pedestrian access is included in Chapter 29: Pedestrian Integration and Chapter 31: Bicycle and Pedicab Integration.\par
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		\fignote{70}{The introduction of a pedestrian island between the curbside-turn lane and the crossing can significantly help pedestrians safely cross within the standard two-phase traffic signal.\label{chapter:intersections-and-signal-control:figure:the-introduction-of-a-pedestrian-island-between-the-curbside-turn-lane-and-the-crossing-can-significantly-help-pedestrians-safely-cross-within-the-standard-two-phase-traffic-signal}}{ITDP.}
	}
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		\img{\hsize}{infrastructure/assets/a84aa00b03de5d962ac83d2c26e9435e1a0fdc59.jpeg}
		\fignote{71}{In Chinese cities such as Xi’an, cyclists are given designated waiting areas from which they have priority access to crossing the street.\label{chapter:intersections-and-signal-control:figure:in-chinese-cities-such-as-xian-cyclists-are-given-designated-waiting-areas-from-which-they-have-priority-access-to-crossing-the-street}}{Karl Fjellstrom.}
	}
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		\img{\hsize}{infrastructure/assets/319e99d01e567b69ce2a2402546f74c52e92ada3.jpeg}
		\fignote{72}{In the UK, a priority bicycle stopping area is placed ahead of the stopping line for motorized vehicles.\label{chapter:intersections-and-signal-control:figure:in-the-uk-a-priority-bicycle-stopping-area-is-placed-ahead-of-the-stopping-line-for-motorized-vehicles}}{Lloyd Wright.}
	}
\fi

For cyclists, intersection risks often emanate from turning vehicles that threaten straight movements by the cyclists. Since the motorized vehicles are often traveling much faster than the bicycles, there is a great potential for conflict and risk at turning locations. Cyclists may feel particularly vulnerable when wanting to turn across traffic.\par
% @ guide/24-intersections_and_signal_control/249-integrating-pedestrian-and-cyclist-movements.src: lines 47-50: code points 1-36

There are at least two mechanisms for permitting cyclists to safely navigate intersections:\par
% @ guide/24-intersections_and_signal_control/249-integrating-pedestrian-and-cyclist-movements.src: lines 52-53: code points 1-0

\begin{itemize}
\item Infrastructure giving physical priority to cyclists and allowing them to cross prior to private vehicles; and\slash{}or,% @ guide/24-intersections_and_signal_control/249-integrating-pedestrian-and-cyclist-movements.src: lines 53-55: code points 1-0
\item Dedicated signalization for cyclists.% @ guide/24-intersections_and_signal_control/249-integrating-pedestrian-and-cyclist-movements.src: lines 55-55: code points 1-43
\end{itemize}
% @ guide/24-intersections_and_signal_control/249-integrating-pedestrian-and-cyclist-movements.src: lines 53-55: code points 1-43

In several countries, dedicated areas located in front of the stopping line for motorized vehicles have been an effective option (Figures 24.71 and 24.72). The idea is to give cyclists a head start over motorized vehicles in crossing the intersection. The cyclists are given a designated box to wait for the green signal phase. In some cases, this physical priority can be combined with an advanced green signal phase as well.\par
% @ guide/24-intersections_and_signal_control/249-integrating-pedestrian-and-cyclist-movements.src: lines 57-61: code points 1-21

A schematic of the bicycle priority measures utilized in Xi’an is given in Figure 24.73 for each of the two signal phases.\par
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		\fignote{73}{Schematic of the dedicated waiting area utilized for bicycles wishing to make cross-traffic turns in Xi’an.\label{chapter:intersections-and-signal-control:figure:schematic-of-the-dedicated-waiting-area-utilized-for-bicycles-wishing-to-make-cross-traffic-turns-in-xian}}{ITDP}
	}
\fi

\section{10}{Grade Separation}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:grade-separation}
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 1-529: code points 1-0

\quotation{Conflict can and should be handled constructively; when it is, relationships benefit. Conflict avoidance is not the hallmark of a good relationship. On the contrary, it is a symptom of serious problems and of poor communication.}{Harriet B. Braiker, psychologist, expert on stress management, 1948-}
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Grade separation brings many benefits from the perspective of travel time savings by raising intersection capacity for both BRT vehicles and mixed traffic vehicles. But the infrastructure can be costly, depending on local circumstances. In many instances, the time savings to BRT customers and to private vehicles will fully justify the added infrastructure costs, but limited capital resources will typically constrain infrastructure expenditures.\par
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\subsection{1}{Criteria for Grade Separation}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:grade-separation:subSection:criteria-for-grade-separation}
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In all of our BRT studies to date we have never really had to resort to a single flyover, meaning that there were always solutions to guarantee BRT operations that would reduce overall current travel times with the available space. In other words: without resorting to grade separation, solutions are likely to be found where the advantages to public transport customers are greater than the hindrance to private vehicle users.\par
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Nonetheless, when the capacity of a four-phase intersection is reaching saturation (more than 450 vehicles\slash{}lane\slash{}hour in 180-second cycle times), it is fairly typical for engineers to suggest the construction of a flyover or an underpass that allows straight movement for one main road (two of the twelve movements), while all other movements remain at the same level. Such general inclinations often lead toward a political understanding that flyover constructions along the BRT corridor are necessary. Besides that, a corridor project usually has to deal with existing flyovers.\par
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The introduction or existence of flyovers or underpasses along the corridor requires special treatments for BRT systems, but they represent an opportunity to dramatically improve BRT vehicle operation. Exclusive busway use of a flyover is a successful technique used in several existing BRT systems despite its potential major adverse visual impacts, which are highly undesirable from an aesthetics standpoint in cities and urban areas.\par
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An ideal separated-grade solution should only let low intensity intersections remain (low enough to not require traffic lights). If it removes mixed traffic and BRT intersections, then it is best to keep BRT at the grade where access is facilitated, likely to be street level with at-grade crossing.\par
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If the grade-separation solution will not eliminate all conflicts, the first option is to use grade-separation infrastructure for BRT usage and exclusively for BRT if needed.\par
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While the discussion in this section is concentrated on flyovers as a means of grade separation, underpasses are frequently the preferred option from an aesthetics standpoint. Generally, the cost of a busway on a flyover will be at least ten times the cost of a normal at-grade busway (per kilometer). The cost of a busway in an underpass will be similar to that of a flyover unless there are adverse subsurface conditions such as the presence of services (utilities), high water tables, or hard rock conditions that may result in underpasses not being technically or economically feasible.\par
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\subsection{2}{Station Location with Grade-Separated Solutions}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:grade-separation:subSection:station-location-with-grade-separated-solutions}
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 47-106: code points 1-55

If the grade-separated solution design maintains BRT lanes through intersections, the same concerns discussed without grade separation about queue blocking the stations apply. When a BRT lane is grade separated, hindering the station is not a concern, but effective pedestrian access becomes a major issue.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 49-51: code points 1-105

In most instances (ramp of 3 percent and headroom of 4 to 5 meters), grade separation will require placing the stations more than three hundred meters away from the intersection. This siting restriction will add walking time for customers travelling between the station and the intersection and nearby destinations adjacent to the area. Quito’s Central Norte line uses grade separation quite effectively with tunnels whisking BRT vehicles through congested intersections. However, the tunnels also imply that at important destinations, such as the Plaza de las Américas, the closest station is a considerable distance away (Figure 24.74). Thus, for the likely high number of customers using this busy area, the time savings from the grade separation can essentially be lost due to the longer walk.\par
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\ifxetex
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		\fignote{74}{In the case of Quito’s Central Norte line, the presence of a BRT underpass has meant that the closest station to a key destination, the Plaza of Américas commercial center, is several hundred meters away.\label{chapter:intersections-and-signal-control:figure:in-the-case-of-quitos-central-norte-line-the-presence-of-a-brt-underpass-has-meant-that-the-closest-station-to-a-key-destination-the-plaza-of-amricas-commercial-center-is-several-hundred-meters-away}}{Lloyd Wright.}
	}
\fi

As an alternative to obtain intersection efficiency (with time savings that serve all customers through the section) at the cost of a convenient station location (that serves local-specific customers), it is possible to place the station beneath or above the intersection. The Metro Center station of the Washington Metro exits directly into the basement floors of commercial shops. In such cases, though, accessing ground-level shops and offices will require a grade transfer for customers, implying either stairs, escalators, and\slash{}or elevators.\par
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Both the Brisbane and Ottawa BRT systems site stations at the tunnel level. In Brisbane, the station is just before the tunnel and thus provides good customer access to local destinations (Figure 24.75). In Ottawa, the station connects directly to a commercial shopping center (Figure 24.76). Further, in the case of Ottawa, the tunnel station nicely protects customers from the harsh winter weather. Quito also has achieved great success with its Villa Flora station, which goes beneath a heavily trafficked roundabout on Maldonado Avenue (Figure 24.77).\par
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		\fignote{75}{Placing stations just before a BRT tunnel, as in Brisbane, helps customers comfortably access local destinations. Image\label{chapter:intersections-and-signal-control:figure:placing-stations-just-before-a-brt-tunnel-as-in-brisbane-helps-customers-comfortably-access-local-destinations-image}}{Queensland Transport.}
	}
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		\img{\hsize}{infrastructure/assets/106de242efceeef07d69145ff70910571b490eaa.jpeg}
		\fignote{76}{A station placed inside a tunnel in Ottawa provides easy access and weather protection.\label{chapter:intersections-and-signal-control:figure:a-station-placed-inside-a-tunnel-in-ottawa-provides-easy-access-and-weather-protection}}{Lloyd Wright.}
	}
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		\fignote{77}{BRT Quito’s Villa Flora roundabout traffic with underpasses.\label{chapter:intersections-and-signal-control:figure:brt-quitos-villa-flora-roundabout-traffic-with-underpasses}}{Google Earth.}
	}
\fi

Effective pedestrian access as well as visually neutral solutions can be designed. For TransMilenio Phase II’s “Avenida Boyacá” station along the Avenida Suba Corridor, the solution was to locate the station above Avenida Boyacá, level with the flyover. Pedestrians access the platform via an elevator from a small pedestrian plaza where fares are collected. This solution allowed for the strategic location of this station, which will make future transfer points on the projected Avenida Boyacá closer to each other. Ultimately, the implementation of solutions of this sort will depend on budgetary constraints.\par
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		\fignote{78}{TransMilenio’s Boyacá Station is on the flyover on Suba Corridor, allowing access from Avenida Boyacá below.\label{chapter:intersections-and-signal-control:figure:transmilenios-boyac-station-is-on-the-flyover-on-suba-corridor-allowing-access-from-avenida-boyac-below}}{Google Street View.}
	}
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		\fignote{79}{TransMilenio’s Boyacá Station entrance below flyover is through a small pedestrian plaza along Avenida Boyacá.\label{chapter:intersections-and-signal-control:figure:transmilenios-boyac-station-entrance-below-flyover-is-through-a-small-pedestrian-plaza-along-avenida-boyac}}{Google Street View.}
	}
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		\fignote{80}{Seen from the flyover on Suba Corridor, TransMilenio’s Boyacá Station seems a regular large station with underground access.\label{chapter:intersections-and-signal-control:figure:seen-from-the-flyover-on-suba-corridor-transmilenios-boyac-station-seems-a-regular-large-station-with-underground-access}}{Google Street View.}
	}
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		\fignote{81}{TransMilenio’s Boyacá Station on the flyover is an example of adapting BRT to existing grade separation.\label{chapter:intersections-and-signal-control:figure:transmilenios-boyac-station-on-the-flyover-is-an-example-of-adapting-brt-to-existing-grade-separation}}{Google Street View.}
	}
\fi

\subsection{3}{Restricting Turning Movements Together with Grade Separation}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:grade-separation:subSection:restricting-turning-movements-together-with-grade-separation}
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 109-487: code points 1-113

As said in the introduction to this section, unless all vehicle intersections are eliminated from the BRT lane by the separated-grade solution, the first option is to consider grade-separation infrastructure to be used by the BRT. In such cases, the concern is to determinate if cost of a separated-grade station can be afforded and is justified by the time saved by users of that station. This cost consists of the infrastructure and\slash{}or the time losses generated to private vehicle users that will lose a second or a third lane on the separated-grade infrastructure (and if it is politically affordable, too).\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 111-116: code points 1-92

A second possibility is to direct BRT vehicles to the flyover in mixed traffic (see Section 24.7: Merging with Mixed Traffic in Narrow Sections), which will result in stations being far from the intersections. Additionally, this configuration can be particularly problematic if there is a connecting BRT corridor running on the perpendicular street below the flyover or above the underpass.\par
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The third possibility is building the flyover on the road perpendicular to the BRT corridor. In this case, the flyover does not introduce any special difficulty in relation to the (same-level) intersection already discussed and if it cannot eliminate the intersection with mixed traffic, it can certainly alleviate the intensity and the number of conflicts, increasing the BRT green time (as this subsection will lead us to conclude by analyzing the following last possibility).\par
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The last possibility is that the flyover is designated for mixed traffic alone and BRT remains on the street level. As the others do not create intersection with BRT, this fourth possibility is only of interest for the remainder of this subsection (though all four must be considered when evaluating benefits).\par
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		\fignote{82}{Schematic of Delhi roadway in which BRT vehicles must cross mixed traffic that is attempting to access a flyover. Image\label{chapter:intersections-and-signal-control:figure:schematic-of-delhi-roadway-in-which-brt-vehicles-must-cross-mixed-traffic-that-is-attempting-to-access-a-flyover-image}}{Elebeta.}
	}
\fi

If a single flyover in the median is built, the BRT vehicles in the median will have to cross the mixed traffic going onto the flyover. This scenario creates either the need for a new signalized intersection prior to the flyover, or a merging lane where the BRT buses and mixed traffic can cross, introducing possible delay and confusion for both the BRT system and the mixed traffic. Figure 24.82 shows the conflict.\par
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		\fignote{83}{In Senen Street, TransJakarta interlaces with mixed traffic to avoid the flyover and reach the station near the intersection. The restart of the bus lane is on the ground level, close to the flyover. The flyover has two lanes and only two more are available to reach the intersection below it. The covered pedestrian flyover seen at the left is a link between the inside area of stations in BRT Corridor 2 and Corridor 6 as the user cannot leave the system’s “paid areas.”\label{chapter:intersections-and-signal-control:figure:in-senen-street-transjakarta-interlaces-with-mixed-traffic-to-avoid-the-flyover-and-reach-the-station-near-the-intersection-the-restart-of-the-bus-lane-is-on-the-ground-level-close-to-the-flyover-the-flyover-has-two-lanes-and-only-two-more-are-available-to-reach-the-intersection-below-it-the-covered-pedestrian-flyover-seen-at-the-left-is-a-link-between-the-inside-area-of-stations-in-brt-corridor-2-and-corridor-6-as-the-user-cannot-leave-the-systems-paid-areas}}{Google Maps.}
	}
\fi

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	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/b59ca32455af96a42c9ee149ab4bd56a052f8378.png}
		\fignote{84}{Alternative design for a flyover that allows BRT vehicles to proceed without conflicts to the area below the flyover.\label{chapter:intersections-and-signal-control:figure:alternative-design-for-a-flyover-that-allows-brt-vehicles-to-proceed-without-conflicts-to-the-area-below-the-flyover}}{Elebeta.}
	}
\fi

If two separate access lanes are constructed for the flyover, one for each traffic direction, it is possible to leave a space between them for the BRT system to continue along the surface as in Figure 24.84.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 150-152: code points 1-6

In this configuration, the BRT will intersect the crossing street under the flyover, so we must consider the alternatives of Section 24.5 with the introduction of the flyover to reduce the number of phases. We present the results of a scenario in which BRT has a green signal with the insertion of a grade-separation infrastructure of two lanes per way (Figures 24.87 to 24.89), maintaining the assumptions in subsection 24.5.4: volumes are equal in all approaches, right and left turns each represent 25 percent of the demand and no U-turns are allowed (therefore 50 percent of traffic is straight), no pedestrian-only phases are required (it is possible to cross the intersection with the given phases), and 90 seconds is still the cycle time of reference.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 154-161: code points 1-24

Although the flyover can cause the impression that four new lanes are created, no mid-block extra width is created (Figures 24.82 and 24.84). Eventually the intersection under the flyover can have some extra width, but usually two lanes near the median are used to place the supporting structure of the flyover, so there is in fact only two extra lanes in the intersection as a whole. Below, we will evaluate the uninterrupted flow in these four lanes.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 163-167: code points 1-39

In our example, the first problem with the mixed traffic comes at the point of flyover access, as half of the traffic has turning intentions, and if permitted to do this, turns at the intersection (under the flyover or above the tunnel) are not enough. Or, if the detours start after the ramp begins, the single lane given for mixed traffic to stay on the flyover is not enough. Widening or sharing space with BRT is required. The solution presented in Section 24.7 does not apply here without further complications as there are two downstream sections (overpass and ground) to be managed. Designing with the assumption that the intersection will not congest because the design is good for the forecast demand is simply naive: when it comes to cars, all the designer can expect is to improve capacity, and sooner or later congestion will return. Given our goals, placing BRT in a shared space with cars in this potential bottleneck is a bad proposal.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 169-178: code points 1-15

So the maximum capacity we present for mixed traffic is still subject to the intersection below the flyover working well. If it gets congested, access to the flyover will also be congested. For proper comparison with the solutions without grade separation, and also because the effective access to the “intersection plus flyover” set has three lanes for mixed traffic, we present the results per lane, assuming each intersection approach has three lanes, as detailed below:\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 180-185: code points 1-0

\begin{itemize}
\item \emphasis{Average lane capacity:} the average of the mixed-traffic lanes’ capacity that would be measured at the stop lines approaching the main intersection. On the presence of a flyover, mixed traffic parallel to the BRT’s approach is considered three lanes, but only two of these were effectively used to balance the traffic sign);% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 185-189: code points 1-0
\item \emphasis{Overall intersection capacity per lane:} in the loop configuration, vehicles pass twice through stop lines in order to execute a cross-traffic turn, and the second pass does not count toward this capacity, but rather it is the same result described in the “average lane capacity” above, except that it does not count the second passage of the same vehicle across the intersection.% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 189-193: code points 1-0
\item \emphasis{Total throughput with flyover and auxiliary intersections per lane at intersection:} this adds in the flows that were completely diverted away from the main intersection (detours and flyover) as if they were effectively passing through the intersection. By bringing the value to the number of lanes of the intersection, this presents a practical estimate of how much the capacity of the main intersection can be pushed to benefit from using the auxiliary ones and flyover as a whole.% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 193-197: code points 1-78
\end{itemize}
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 185-197: code points 1-78

Options where the detours are below the flyover assume that the height clearance makes it possible, which is not always the case. Access ramps to and from perpendicular streets may also be taken into account in order to make turning detours on the flyover possible.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 199-202: code points 1-0

\tabletitle{5}{Flyover Capacity Examples}
\label{chapter:intersections-and-signal-control:table:flyover-capacity-examples}
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	\color{gray75}\bfseries Option& \color{gray75}\bfseries Cycle Time (seconds)& \color{gray75}\bfseries Phases& \color{gray75}\bfseries BRT Direction Straight Flow& \color{gray75}\bfseries BRT Direction Curb-Side-Turn Detour& \color{gray75}\bfseries BRT Direction Cross-Traffic-Turn Detour& \color{gray75}\bfseries Perpendicular Direction Curb-Side-Turn Detour& \color{gray75}\bfseries Perpendicular Direction Cross-Traffic-Turn Detour& \color{gray75}\bfseries Figure& \color{gray75}\bfseries BRT Green Time (seconds)& \color{gray75}\bfseries Average Lane Capacity (pcu\slash{}hour)& \color{gray75}\bfseries Overall Intersection Capacity per Lane (pcu\slash{}lane)& \color{gray75}\bfseries Total Throughput with Auxiliary Intersections per Lane at Intersection \cr
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% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 202-413: code points 1-9

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/cc3dc3272982e3dd0ee3c1332b7fccc280fa10cb.jpeg}
		\fignote{85}{While vehicles in mixed traffic can bypass a congested intersection in Bangkok, public transport vehicles are often consigned to serving stations near the intersection. This can result in slow average speeds for public transport.\label{chapter:intersections-and-signal-control:figure:while-vehicles-in-mixed-traffic-can-bypass-a-congested-intersection-in-bangkok-public-transport-vehicles-are-often-consigned-to-serving-stations-near-the-intersection-this-can-result-in-slow-average-speeds-for-public-transport}}{Lloyd Wright.}
	}
\fi

Option A1 is fairly common with conventional bus services (as in Bangkok, Figure 24.85) and BRT (as in Jakarta, Figure 24.86). Mixed-traffic vehicles have access to the flyover and thus are given a substantial priority at the intersection. By contrast, public transport vehicles servicing the intersection area are often mired in heavy congestion. There is limited benefit of using a flyover or underpass if a four-phase signal timing is maintained. In our established scenario, the overall increase in the whole intersection capacity is quite small, with the capacity only rising from 395 pcu\slash{}lane\slash{}hour to 439 pcu\slash{}lane\slash{}hour.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 419-424: code points 1-99

\ifxetex
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\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/f0995896506a599a2d17c6e6a813fb6f345eac20.png}
		\fignote{86}{This five-leg intersection under the Senen Street flyover in Jakarta has several forbidden turns; the intersection of two BRT corridors and a four phase-signal causes delays in both corridors and is even worse than mixed traffic.\label{chapter:intersections-and-signal-control:figure:this-five-leg-intersection-under-the-senen-street-flyover-in-jakarta-has-several-forbidden-turns-the-intersection-of-two-brt-corridors-and-a-four-phase-signal-causes-delays-in-both-corridors-and-is-even-worse-than-mixed-traffic}}{Google Maps.}
	}
\fi

Using three phases, moving from option E to option E1, curiously adds no benefit with the use of the flyover. Even with 50 percent of the traffic being diverted to the flyover and the reduction of the approach parallel to the BRT from three to two lanes (while one lane is used for cross-traffic turns), only one lane is able to process both curbside turns, and cross-traffic turns from the perpendicular direction all result in the same relative green distribution with or without the flyover. But mixed traffic using only one lane for such a long phase (the same as the BRT phase) reduces the intersection’s overall capacity substantially (71.5 percent). Adding the flow on the flyover (60 percent) results in exactly what is coincidentally the same overall capacity as having an intersection plus flyover.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 430-437: code points 1-80

Without a flyover, the best observed configurations consist of the following options: (Option I from Table 4.5, Figure 24.87) doing all detours on the curbside parallel street to turn onto the desired direction once the other street is reached, letting only straight flows in the perpendicular street and in the flyover is the Option (I1) that results in larger capacity for mixed traffic and not coincidentally the shortest green time for the BRT (27 seconds), except for the four-stage alternative (A1). That happens because the only conflict left at the main intersection is perpendicular straight flow (in three lanes) against perpendicular cross-traffic turn (in two lanes). Having 63 seconds of red time may not be unbearable for a low frequency BRT, but it will almost certainly not allow a station to be positioned between the two intersections (the main and the auxiliary), since the resulting saturation for the conjunct station plus intersection will be much higher than that of a station alone.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 439-448: code points 1-67

\ifxetex
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\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/51345592e8c0d36b43432d7bc265c2c383786b38.png}
		\fignote{87}{Curbside detour for perpendicular flows under the flyover.\label{chapter:intersections-and-signal-control:figure:curbside-detour-for-perpendicular-flows-under-the-flyover}}{Elebeta.}
	}
\fi

Applying the same scheme, but using the flyover (Option I2, Figure 24.88), moves all the conflicts to the secondary intersection, which ends up being the capacity limiting element for the conjunct. As there are only two lanes in the flyover to handle the straight flow plus the cross-traffic flow from both directions (i.e., double flow in two-thirds of lanes), its result is worse than some alternatives without a flyover.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 452-456: code points 1-18

\ifxetex
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	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/35bc00bcb575503a62406c64c645025e3c3ce0d7.png}
		\fignote{88}{Curbside detour for perpendicular flows above the flyover.\label{chapter:intersections-and-signal-control:figure:curbside-detour-for-perpendicular-flows-above-the-flyover}}{Elebeta.}
	}
\fi

For the clovelike alternatives (Options K, K1, K2), adding the flyover and maintaining the loops on the ground (Option K1) raises overall capacity for the system by 15 percent (comparing with option K). Making detours in auxiliary streets to take the bridge (Option K2, figure 24.89) will make it look like a “real-clove interchange” and, except for the BRT, there would be no intersection (pedestrian phase is required now). Therefore, the BRT phase would be the minimal 10 seconds and an equivalent average capacity of lanes would be 1,520 pcu\slash{}hour. Nevertheless, as all vehicles willing to do cross-traffic turns at the intersection use it twice, this is equivalent to “only” 1,216 pcu\slash{}hour.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 460-466: code points 1-84

\ifxetex
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\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/f2b32ddd1dc7fc3969b825c05035bc32a8cd53f2.png}
		\fignote{89}{Clovelike intersection.\label{chapter:intersections-and-signal-control:figure:clovelike-intersection}}{Elebeta.}
	}
\fi

The fact that this situation is equivalent to a BRT cross only, the cycle time can be reduced to BRT maximum red time requirements. If this requirement is 50 seconds, then the intersection cycle can be 60 seconds (Option K3) and equivalent overall capacity is reduced to 992 pcu\slash{}hour\slash{}lane. If it is 35 seconds (maybe enough to bring the station 20 meters from the intersection and fit under the flyover), the cycle has to be 45 seconds (Option K4) and capacity is further reduced to 992 pcu\slash{}hour in our example.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 470-474: code points 1-96

Although generic, the assumptions of this exercise are quite common, so there is a strong suggestion that:\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 476-478: code points 1-0

\begin{itemize}
\item Without grade separation, reducing signal phases to two can provide solutions as good as many grade-separated solutions in terms of capacity for mixed traffic and results in better BRT green times than grade-separated solutions.% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 478-481: code points 1-0
\item To prioritize BRT green times and meaningfully increase capacity, the use of separated-grade solutions must be cleverly associated with turn restrictions, and the \emphasis{best solutions are obtained if the flyover is on the perpendicular road} (had that been the case of options I1 and K2, green times for the BRT would be respectively 54 and 76 seconds in a cycle of 90 seconds).% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 481-484: code points 1-60
\end{itemize}
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 478-484: code points 1-60

As mentioned before, an intersection cannot be analyzed in isolation. Optimum results are usually obtained when vehicle movements are analyzed along the corridor and the entire extended area surrounding the intersection.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 486-487: code points 1-113

\subsection{4}{BRT Turning with Grade-Separated Solutions}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:grade-separation:subSection:brt-turning-with-grade-separated-solutions}
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 490-514: code points 1-100

Separated-grade infrastructure can also be used to provide the dedicated turns for the BRT. For heavy traffic corridors where free-flow turning is required to avoid breaking down the system, the time savings certainly justify the costs.\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 492-494: code points 1-28

Bogotá utilizes grade separation to provide dedicated turning infrastructure to BRT operations, such as overpasses and underpasses that link the corridors of 80th Street and Norte-Quito-Sur to an exclusive BRT roundabout (Figures 24.90 and 24.91), as well as provide an exceptional BRT-only third-floor roundabout completed in 2015 to guarantee that the interchange in Norte-Quito-Sur and Calle 6 has no delays (Figures 24.92 and 24.93).\par
% @ guide/24-intersections_and_signal_control/2410-grade-separation.src: lines 496-500: code points 2-17

\ifxetex
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\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/b82112d84ef3adfecc9b14595e8cfb25f7128e89.jpeg}
		\fignote{90}{At the major intersection of TransMilenio’s Calle 80 corridor and NQS corridor is a set of underpasses and an overpass link to the exclusive BRT roundabout.\label{chapter:intersections-and-signal-control:figure:at-the-major-intersection-of-transmilenios-calle-80-corridor-and-nqs-corridor-is-a-set-of-underpasses-and-an-overpass-link-to-the-exclusive-brt-roundabout}}{Google Earth.}
	}
\fi

\ifxetex
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	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/f790bd307d12e32c348dfa606e059315bf53b645.jpeg}
		\fignote{91}{An exclusive roundabout facilitates exclusive turning movements for BRT vehicles between two corridors: the NQS corridor and Calle 80 corridor.\label{chapter:intersections-and-signal-control:figure:an-exclusive-roundabout-facilitates-exclusive-turning-movements-for-brt-vehicles-between-two-corridors-the-nqs-corridor-and-calle-80-corridor}}{Eduardo Plata and Por el País que Queremos (PPQ).}
	}
\fi

\ifxetex
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	{  % group required to avoid fignote settings escaping
		\img{\hsize}{infrastructure/assets/bc5b3f6690234e6113df7e03cfb282972caa262e.jpeg}
		\fignote{92}{This TransMilenio interchange was carefully planned from an operational and aesthetic point of view.\label{chapter:intersections-and-signal-control:figure:this-transmilenio-interchange-was-carefully-planned-from-an-operational-and-aesthetic-point-of-view}}{Instituto de Desarollo Urbano de Bogotá.}
	}
\fi

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		\img{\hsize}{infrastructure/assets/84fc934d15bd8662d60f31d454aa9044c14641e0.jpeg}
		\fignote{93}{Exclusive BRT third-floor roundabout is an unprecedented work of art to guarantee free-flow movements for TransMilenio operation.\label{chapter:intersections-and-signal-control:figure:exclusive-brt-third-floor-roundabout-is-an-unprecedented-work-of-art-to-guarantee-free-flow-movements-for-transmilenio-operation}}{Instituto de Desarollo Urbano de Bogotá.}
	}
\fi

\subsection{5}{BRT through Roundabouts with Grade-Separated Solutions}
\label{volume:infrastructure:chapter:intersections-and-signal-control:section:grade-separation:subSection:brt-through-roundabouts-with-grade-separated-solutions}
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Constructing a busway underpass that goes below the roundabout and avoids all conflicts with mixed traffic—and thus promotes time savings for both BRT and mixed traffic—is also a possibility, as the examples from Quito with good and bad station locations show (Figures 24.74 and 24.94).\par
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\ifxetex
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		\img{\hsize}{infrastructure/assets/307c0b48a78fff6f44be2e715a99076c9d5f2cc5.png}
		\fignote{94}{Quito’s BRT avoids the Villa Flora roundabout traffic with underpasses.\label{chapter:intersections-and-signal-control:figure:quitos-brt-avoids-the-villa-flora-roundabout-traffic-with-underpasses}}{Google Earth.}
	}
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A flyover is also a possibility, but the design of an aesthetically acceptable solution is very challenging. With the exception of the exceptional third-floor roundabout above mixed traffic in Bogotá as mentioned in the previous section, there are no other readily available examples of an aesthetically acceptable flyover.\par
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