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\chapter{8}{Traffic-Impact Assessment}
\label{volume:operations:chapter:traffic-impact-assessment}
% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 1-4: code points 1-85

\quotation{A life is not important except in the impact it has on other lives.}{Jackie Robinson, first African American to play in Major League Baseball, 1919–1972}
% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 3-4: code points 1-85

Any changes in a transportation network could result in changes to the operations of that network. This also applies to the introduction of a BRT system along city streets and arterials. The planning of a BRT system typically follows an iterative process to identify the best routes. One of the criteria to consider is the impact of the BRT on general mixed-traffic operations. For this reason, the traffic impacts need to be understood and quantified even during the planning and preliminary phases of a BRT system. The major reasons for conducting traffic-impact assessments are:\par
% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 6-11: code points 1-72

\begin{itemize}
\item Impacts of general traffic on BRT operations:\highlight{ }Congestion at intersections that could have an impact on vehicle operations or queue spill-backs from neighboring intersections should be defined and mitigated, the main purpose being to ensure zero impact on vehicle operations during all hours of the day;% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 13-16: code points 1-8
\end{itemize}
% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 13-16: code points 1-8

\begin{itemize}
\item Impacts of BRT on general-traffic operations: Departments responsible for general traffic require quantification of the possible traffic impacts of the BRT implementation and also, where necessary, assurances that negative impacts can be mitigated;% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 18-20: code points 1-39
\end{itemize}
% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 18-20: code points 1-39

\begin{itemize}
\item Required environmental procedures: Many cities have environmental legislation, which requires evaluation of all impacts, and any proposed mitigation measures.% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 22-23: code points 1-64
\end{itemize}
% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 22-23: code points 1-64

In many cities, the impact of public transit vehicles operating in mixed traffic on the operations of the facility can be severe due to the way the services are operated, such as the frequent starting and stopping in mixed-traffic lanes, pulling out and merging where stops are at the curb, and undisciplined lane changing and driver behavior. Introducing a BRT service with the focus of formalizing the public transit services into dedicated lanes will remove the disruptive operations of the current public transit services, and will improve the operations for mixed traffic. This could not only improve travel times for all private vehicles, but could also have a positive impact on business-travel and freight movements during all times of the day.\par
% @ guide/08-traffic-impact-assessment/00-traffic-impact-assessment.src: lines 26-33: code points 1-28

\ifxetex
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		\img{\hsize}{operations/assets/f3712e9f640d68d27b3dc62567355f90211cf67d.jpeg}
		\fignote{1}{The Gangding conventional bus stop,in Guangzhou, China\label{chapter:traffic-impact-assessment:figure:the-gangding-conventional-bus-stopin-guangzhou-china}}{Karl Fjellstrom, itdp-china.org.}
	}
\fi

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{operations/assets/2a8938aadbbc8f8e6db7a226260d0c84b97143ed.jpeg}
		\fignote{2}{The Gangding BRT station in Guangzhou, China. Despite 24 meters being taken from the center of the roadway for the BRT stations and roadways, both capacity and speed of the road for mixed traffic and buses improved dramatically. Conditions for pedestrians were also greatly improved, with customers waiting in the station rather than on the side of the road.\label{chapter:traffic-impact-assessment:figure:the-gangding-brt-station-in-guangzhou-china-despite-24-meters-being-taken-from-the-center-of-the-roadway-for-the-brt-stations-and-roadways-both-capacity-and-speed-of-the-road-for-mixed-traffic-and-buses-improved-dramatically-conditions-for-pedestrians-were-also-greatly-improved-with-customers-waiting-in-the-station-rather-than-on-the-side-of-the-road}}{Duan Xiaomei, GMEDRI}
	}
\fi

\section{1}{Requirements for a Traffic-Impact Assessment}
\label{volume:operations:chapter:traffic-impact-assessment:section:requirements-for-a-traffic-impact-assessment}
% @ guide/08-traffic-impact-assessment/81-requirements-for-a-traffic-impact-assessment.src: lines 3-14: code points 1-0

Traffic-Impact Assessments (TIAs) could be required for several reasons. First, the planners and designers of the BRT system need to ensure that the system will work and that the possible adverse impacts on the general traffic are mitigated, or at least quantified and understood by all involved. Second, the authorities and\slash{}or departments within the authority that are responsible for the road network who need to approve the plans will often require the quantification of all transport-related impacts. Third, in many countries the environmental management legislation requires all impacts of new developments to be quantified and mitigated. This will require a full TIA. Last, the people, property owners, and business owners that could be affected by the proposed BRT will require details of the impacts and how they will affect their lives, properties, and businesses.\par
% @ guide/08-traffic-impact-assessment/81-requirements-for-a-traffic-impact-assessment.src: lines 5-14: code points 1-0

\section{2}{Data Needs}
\label{volume:operations:chapter:traffic-impact-assessment:section:data-needs}
% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 3-37: code points 1-19

\quotation{Data is not information, information is not knowledge, knowledge is not understanding, understanding is not wisdom.}{Clifford Stoll, astronomer, 1950-}
% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 5-6: code points 1-35

For any detailed traffic-engineering study, data representing the existing conditions will be required. This will form the baseline against which proposed alternatives can be compared, and which can be used for future traffic projections. During the planning stages of the project, data should have been collected with the focus on link volumes and distribution of traffic volumes during the day. This data would typically include classified hourly counts of both vehicle (classified by vehicle type) and customer volumes (occupancies in vehicles). Also from the planning stages of the project, data such as Origin-Destination patterns (OD Patterns), vehicle occupancies, existing public transit ridership, and an assessment of possible modal shifts should be available. This information should be sourced for input and evaluation in the Traffic Impact Assessment. Depending on the detail required for the TIA and the extent of the TIA, it could be necessary to collect the following additional information:\par
% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 8-17: code points 1-67

\begin{itemize}
\item {Classified vehicle turning movement counts at all the major intersections;\par
% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 19-20: code points 7-0

\begin{itemize}
\item These counts must be categorized in fifteen-minute intervals and done for at least two hours (preferably three hours) during each typical peak period of a typical day;% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 20-22: code points 1-0
\item Where significant issues are expected during shopping peaks on Saturdays or Sundays, these peak periods should also be counted;% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 22-24: code points 1-0
\item The counts must be classified by type, i.e., cars, buses, minibuses, paratransit, trucks, pedestrians, and bicycles;% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 24-25: code points 1-13
\end{itemize}
% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 20-25: code points 1-13

}
\item Turning-movement counts at the major accesses along the corridor with similar requirements for the counts as outlined above;% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 26-28: code points 1-0
\item Link-volume counts (between major intersections) classified by vehicle type on all the major routes in the proposed BRT corridors and also along important parallel routes. These counts should preferably be done for a full day in order to define the variation in traffic demand over a typical day, not only in terms of the total traffic volume, but also the variation in demand for each of the different modes;% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 28-32: code points 1-0
\item {If not available from the local agencies or from the planning studies for the BRT, the following information must also be collected (see Chapter 4);\par
% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 32-34: code points 7-0

\begin{itemize}
\item Vehicle occupancies;% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 34-35: code points 1-0
\item Modal shift;% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 35-36: code points 1-0
\item Public transit ridership;% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 36-37: code points 1-0
\item OD patterns.% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 37-37: code points 1-18
\end{itemize}
% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 34-37: code points 1-18

}
\end{itemize}
% @ guide/08-traffic-impact-assessment/82-data-needs.src: lines 19-37: code points 1-19

\section{3}{Study Area and Extent of Assessment}
\label{volume:operations:chapter:traffic-impact-assessment:section:study-area-and-extent-of-assessment}
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\quotation{All you need is the plan, the road map, and the courage to press on to your destination.}{Earl Nightingale, author, 1921–1989}
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Study areas for traffic-impact assessments are often well defined in local guidelines and are mostly based on the extent of the increase in traffic demand through the network and specifically through critical intersections. The introduction of BRT operations should not result in an increase in traffic volumes, but in fact should reduce the number of single-vehicle occupancy trips along a corridor. However, there will be impacts along the route and parallel routes as a result of:\par
% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 8-12: code points 1-67

\begin{itemize}
\item The possible removal of general-traffic lanes;% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 14-15: code points 1-0
\item The possible removal of parking lanes;% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 15-16: code points 1-0
\item The narrowing of general-traffic lanes;% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 16-17: code points 1-0
\item Signal-timing changes that could result in less green time for general-traffic operations;% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 17-18: code points 1-0
\item Restrictions and banning of certain turning movements at intersections and changes in local turning movements and access patterns;% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 18-20: code points 1-0
\item Diversions from the arterial along which BRT operations are planned due to capacity constraints to alternative parallel routes;% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 20-22: code points 1-0
\item Removal of local bus routes from general-traffic lanes.% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 22-22: code points 1-61
\end{itemize}
% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 14-22: code points 1-61

The traffic impacts are not necessarily restricted to the corridor itself, but could also be introduced on alternative parallel roads. At a minimum, the study area should include the actual corridors along which the BRT is planned, with specific attention to all the major intersections. Ideally, the impact assessment would also include impacts to cross streets and along parallel alternative routes. The purposes of the impact assessment must always be clearly defined, and care should be taken not to introduce unnecessary mitigation measures along the corridor and along alternative routes. The BRT in itself can be argued as a major mitigation measure to improve the capacity of a corridor. Mitigation measures should be restricted to the route along which the BRT is planned unless there are compelling operational reasons to expand improvements to the road network in the immediate vicinity of an intersection where, for example, turning movements are banned and\slash{}or restricted as a result of the BRT system.\par
% @ guide/08-traffic-impact-assessment/83-study-area-and-extent-of-assessment.src: lines 24-33: code points 1-69

\section{4}{Level of Analysis}
\label{volume:operations:chapter:traffic-impact-assessment:section:level-of-analysis}
% @ guide/08-traffic-impact-assessment/84-level-of-analysis.src: lines 3-44: code points 1-10

\quotation{The analysis of the thing is not the thing itself.}{Aaron Allston, novelist, 1960–2014}
% @ guide/08-traffic-impact-assessment/84-level-of-analysis.src: lines 5-6: code points 1-36

The impact analysis can be done at various levels of detail. This will depend on the specific needs of the planning and design team and on the requirements of the responsible authorities. The level of analysis can vary from a course \emphasis{Planning Level}, to an \emphasis{Operational Analysis}, and down to a very detailed \emphasis{Microscopic Simulation} level. The purpose of the analysis should be to get a thorough understanding of the current traffic volumes and the current operations during all the critical time periods of a typical weekday. These will include at least the normal morning and afternoon\slash{}evening commuter peaks, but if necessary the midday commercial and possible weekend peak hours should also be evaluated. The three levels of analysis are not mutually exclusive but can be performed in steps or phases and can be described as follows:\par
% @ guide/08-traffic-impact-assessment/84-level-of-analysis.src: lines 8-16: code points 1-8

\begin{itemize}
\item \emphasis{Planning and Preliminary Analysis:} The first phase of analysis is normally a Planning Level analysis, which should be conducted during the planning phase of the project, but can also be applied during the detailed analysis phase of the project. The planning analysis allows for the use of default input values instead of using more relevant field-measured values. The results of the planning level analysis should be sufficient to clearly indicate which elements of the transportation network are currently, or with the future BRT system, at or over capacity and require mitigation, or which elements will be operating well below capacity and require no mitigation. Based on the results of the planning analysis, the project team and\slash{}or the relevant authority can then decide on doing a more detailed operational analysis of the network elements where the desired operational outcomes will not be met, i.e., those elements where the transport demand will exceed the capacity of the element;% @ guide/08-traffic-impact-assessment/84-level-of-analysis.src: lines 18-28: code points 1-0
\item \emphasis{Operational Analysis}\emphasis{:} Following the planning analysis, the next level of analysis will be at an operational level. This is similar to the planning analysis, except the analysis of the critical elements is done in more detail, specifically refining the input assumptions, ensuring that the analysis is based on field-measured variables such as lane-widths, signal timings, gradients, etc. This level of analysis should also include a sensitivity analysis specifically to quantify variation in future operations based on the possible variation in input assumptions. For example, the future traffic demand will depend on the modal shift from private to public transport, and this could vary depending on the modal shift. The results of the operational analysis should, in most cases, provide sufficient detail to satisfy the project team and\slash{}or the relevant authorities. However, where additional detail is required for complex intersections or networks, a Microscopic Simulation will be necessary;% @ guide/08-traffic-impact-assessment/84-level-of-analysis.src: lines 28-38: code points 1-0
\item \emphasis{Microscopic Simulation:} This involves the computer simulation of the behavior and movement of individual vehicles, bicycles, and\slash{}or pedestrians on the transportation network. At this level, every detail of the operations based on the predicted demand and the simulated geometric conditions can be assessed. For this analysis to be accurate it needs to include actual field-measured inputs. There are several challenges with microsimulation, of which the most important is the validation of the model against field data. Without validation of the simulation model, the results should be questioned and interpreted with care.% @ guide/08-traffic-impact-assessment/84-level-of-analysis.src: lines 38-44: code points 1-10
\end{itemize}
% @ guide/08-traffic-impact-assessment/84-level-of-analysis.src: lines 18-44: code points 1-10

\section{5}{Estimating Traffic Volumes}
\label{volume:operations:chapter:traffic-impact-assessment:section:estimating-traffic-volumes}
% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 3-36: code points 1-27

\quotation{If you have to forecast, forecast often.}{Edgar R. Fiedler, economist, 1929–2003}
% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 5-6: code points 1-40

The changes in traffic volumes due to the introduction of new BRT corridors are not always simple to determine. BRT is typically introduced along existing public transport corridors where the demand is already serviced by buses or forms of paratransit such as minibuses. In some cities, these existing public transport vehicles can make up as much as 10 percent of the general traffic stream. Because of this, introducing organized BRT services in dedicated lanes, which might require reducing lane capacity for general traffic, might not necessarily have significant negative operational impacts.\par
% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 8-13: code points 1-85

The demand estimation on the network post-implementation of the BRT can be done in the following steps:\par
% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 15-16: code points 1-0

\begin{enumerate}
\item Identify all the design alternatives in terms of new infrastructure, route alignment frequencies, and BRT route capacities;% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 16-18: code points 1-0
\item Remove all the relevant existing buses from the existing mixed-traffic lanes in the corridor. The traffic demand needs to be adjusted to account for the removal of the current public transport volumes on the network. This process should be informed by the planning and phasing of the BRT, since this will guide how many, if any, of the current buses will be removed from the network;% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 18-22: code points 1-0
\item Add the proposed BRT vehicles back to the network, specifically along the corridors where the BRT will operate in mixed traffic;% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 22-24: code points 1-0
\item Determine the extent of any modal shift from private automobiles to the proposed BRT. The modal shift should be defined by the BRT planners, and preferably supported by “Stated Preference” surveys (for more details, refer to Chapter 6: Service Planning). Reduce the private vehicle demand with the estimated shift away from private vehicles to BRT. The modal shift will depend on a variety of factors, one of which is the capacity and delay along the general traffic lanes. Therefore, the estimated network operations as determined in the next step should inform the modal split, hence there could be iteration between Step 4 and 5;% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 24-31: code points 1-0
\item Estimate the possible changes in the capacity of the network for general traffic and determine possible diversions to other routes as a result of the capacity constraints. This could be a result of lanes being reduced due to the exclusive-use requirements of the BRT, or because of traffic-signal timing changes to accommodate the BRT;% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 31-35: code points 1-0
\item Determine localized changes in traffic volume demands due to changes and\slash{}or restrictions to turning movements at intersections.% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 35-36: code points 1-27
\end{enumerate}
% @ guide/08-traffic-impact-assessment/85-estimating-traffic-volumes.src: lines 16-36: code points 1-27

\section{6}{Methodologies and Performance Measures}
\label{volume:operations:chapter:traffic-impact-assessment:section:methodologies-and-performance-measures}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 3-213: code points 1-0

\quotation{Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more.}{Nikola Tesla, inventor, 1856-1943}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 5-6: code points 1-35

Once the traffic volumes for all modes and for the different scenarios are determined for the target year, it is necessary to express the performance of the roadway facility using one or more quantitative measures that characterize the service experienced by the users. These measures are not only useful to the planners and engineers in evaluating options and impacts, but are also beneficial in describing operations to officials, policy makers, administrators, and the public. It is important that the selected measures are well defined and understood by all involved in the project. Performance measures must include all modes. Often an unwarranted focus is placed on the use of a single general-performance measure (i.e., level-of-service), but which is not necessarily universally applicable. The various available measures that could be used to evaluate the traffic impact of BRT systems can be classified into two broad categories: macroscopic and microscopic measures. Macroscopic level measures focus on:\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 8-17: code points 1-74

\begin{itemize}
\item Throughput of the road, arterial, corridor, or wider system, measured in passengers per time unit, typically per hour;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 19-21: code points 1-0
\item Average speeds along the road, corridor, or in the system;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 21-22: code points 1-0
\item System and corridor door-to-door travel times;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 22-23: code points 1-0
\item Vehicle emissions from all modes on the corridor or greater transportation system.% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 23-23: code points 1-88
\end{itemize}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 19-23: code points 1-88

On the microscopic level, the measures relate to:\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 25-25: code points 1-49

\begin{itemize}
\item Specific intersection or bottleneck capacities and demands;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 27-28: code points 1-0
\item Average delay per vehicle;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 28-29: code points 1-0
\item Number of stops per vehicle;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 29-30: code points 1-0
\item The saturation levels of the individual movements at an intersection.% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 30-30: code points 1-75
\end{itemize}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 27-30: code points 1-75

To successfully evaluate the impact of a BRT system, it is essential that not only the performance measures that will be used be defined and confirmed with all stakeholders, but also for the performance-measure criteria to be established and confirmed with all stakeholders. The methodologies and analysis tools that are used to define traffic impacts not only vary among states and provinces in one country, but also vary across the world. However, all methodologies include at least some measure of capacity and a comparison of the expected or current demand and how that relates to the capacity (volume-to-capacity ratio) of the facilities, and often also include operational descriptors such as average speed, average delay, densities, walkability, etc. The latter can be for a specific part of a route (intersection or link), a complete route, or even for a whole corridor or area.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 32-40: code points 1-62

A widely used reference for these types of analyses is the \emphasis{Highway Capacity Manual }(\emphasis{HCM}) developed by the USA Transportation Research Board (TRB). The 2010 edition of the \emphasis{HCM} includes methodologies to estimate individual measures such as automobile travel speed, automobile stop rate, automobile traveller-perception score, pedestrian travel speed, pedestrian space, pedestrian-perception score, bicycle travel speed, bicycle-perception score, public transit vehicle travel speed, public transit wait–ride score, and public transit customer-perception score. It also provides a methodology for combining the individual measures into a single measure for the street, and it is often expressed as a level-of-service (LOS). LOS is also considered a performance measure, and can be computed individually for the automobile, pedestrian, bicycle, and transit travel modes. The individual measures can also be combined to collectively express a single measure for the facility. The latter, a collective approach to describing the performance of the system, is critical for a balanced evaluation of the impact of a BRT system. The \emphasis{HCM} has evolved over the years from an automobile-oriented focus to a comprehensive multimodal focus, the multimodal focus only coming to the fore in the 2010 edition. The new edition puts forth principles and methodologies that are useful to consider for capacity analysis of any part of the transportation system and for most modes.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 42-55: code points 1-94

Although the LOS concept is very useful to describe operations with a single measure, the criteria used to define the various modes are based on North American data and standards. These are not necessarily universally applicable, except possibly the criteria for the automobile modes since they are based on performance measures that are field-measurable. Level of service at intersections is related to ranges of average delay per vehicle, in seconds per vehicle. That means that for a given average delay at a junction, the delay is equally experienced by the 1.2 customers in the private vehicle and the 60 customers in the transit bus. If average delay per customer is used as a performance indicator, instead of delay per vehicle, an improvement for transit vehicles will have a much higher impact on intersection average delay.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 57-65: code points 1-6

The criteria for the pedestrian and bicycle modes, which are based on scores reported by users indicating their perception of service quality, however, may vary from country to country. Similarly, the criteria for the public transit modes, which are based on measured changes in patronage due to changes in service quality, will also vary from country to country. This should be kept in mind, and where necessary adapted for local conditions. This is especially important when evaluating pedestrian and bicycle operations in countries where the behavior and prevalence of these modes are significantly different from that in the United States.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 67-73: code points 1-18

The table below summarizes the capacity methodology for the four major modes and the linkages between the modes and the infrastructure elements. Following the methodology presented in the \emphasis{HCM}, the level of services of all four of the major modes can be determined.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 75-77: code points 1-61

Apart from understanding the relationship between the demand for a facility and the capacity of that facility, it is important to understand the acceptability of the operations. The latter is typically presented as a level-of-service, which is based on predefined criteria and as follows:\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 79-81: code points 1-86

\begin{itemize}
\item Automobiles: travel speed as a percentage of base free-flow speed;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 83-84: code points 1-0
\item Pedestrians: the density of pedestrians on the facility combined with a score which is based on several factors outlined below;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 84-86: code points 1-0
\item Bicycle: a score based on the weighted average bicycle-travel speeds along the facility;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 86-87: code points 1-0
\item Public Transit: a score based on the weighted average speeds of the services along the route.% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 87-87: code points 1-99
\end{itemize}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 83-87: code points 1-99

Level-of-service is denoted by a number ranging from LOS A to LOS F, where LOS A represents the best operations and LOS F represents the worst operations where the demand typically exceeds the capacity of the facility. Table 8.1 illustrates the level-of-service for the automobile mode as a function of travel speed.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 90-93: code points 1-13

\tabletitle{1}{Automobile LOS Criteria}
\label{chapter:traffic-impact-assessment:table:automobile-los-criteria}
\halign to 30\tablemodule{%
	\vtop{\sffamily\footnotesize\noindent\hsize=15\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 Travel Speed as a Percentage of Base Free-Flow Speed (\%)& \color{gray75}\bfseries LOS by Critical Volume-to-Capacity Ratio*& \color{gray75}\bfseries  \cr
	\noalign{\vskip 1mm} \hline \noalign{\vskip 2mm} 
	\color{gray50}&
	\color{gray50}<= 1.0&
	\color{gray50}> 1.0\cr
	\noalign{\vskip 2mm 
}	\color{gray50}>85&
	\color{gray50}A&
	\color{gray50}F\cr
	\noalign{\vskip 2mm 
}	\color{gray50}>67-85&
	\color{gray50}B&
	\color{gray50}F\cr
	\noalign{\vskip 2mm 
}	\color{gray50}>50-67&
	\color{gray50}C&
	\color{gray50}F\cr
	\noalign{\vskip 2mm 
}	\color{gray50}>40-50&
	\color{gray50}D&
	\color{gray50}F\cr
	\noalign{\vskip 2mm 
}	\color{gray50}>30-40&
	\color{gray50}E&
	\color{gray50}F\cr
	\noalign{\vskip 2mm 
}	\color{gray50}<=30&
	\color{gray50}F&
	\color{gray50}F\cr
	\noalign{\vskip 2mm 
}}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 96-129: code points 1-9

\emphasis{Note: }* The critical volume-to-capacity ratio is based on consideration of the through movement volume-to-capacity ratio at each boundary intersection in the subject direction of travel. The critical volume-to-capacity ratio is the largest ratio of those considered.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 131-133: code points 1-66

Source: Highway Capacity Manual, 2010.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 135-135: code points 1-38

The pedestrian LOS presented below is a function of both density of pedestrians and a “score,” which is based on several factors such as:\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 137-138: code points 1-36

\begin{itemize}
\item Widths of the traffic lane, bike lane, shoulders, and sidewalk;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 140-140: code points 1-69
\end{itemize}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 140-140: code points 1-69

\begin{itemize}
\item Buffer presence of open space, on-street parking, and street trees;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 142-142: code points 1-73
\end{itemize}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 142-142: code points 1-73

\begin{itemize}
\item Volumes and speeds of general traffic and permitted turns on red at signals;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 144-144: code points 1-82
\end{itemize}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 144-144: code points 1-82

\begin{itemize}
\item Crossing distance and distance to the nearest cross walk;% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 146-146: code points 1-63
\end{itemize}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 146-146: code points 1-63

\begin{itemize}
\item Pedestrian delay.% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 148-148: code points 1-23
\end{itemize}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 148-148: code points 1-23


			\ifxetex
				% disabled for now
			\else
				{  % group required to avoid fignote settings escaping
					\tabletitle{2}{Pedestrian LOS Criteria}
\label{chapter:traffic-impact-assessment:table:pedestrian-los-criteria}

					\img{\hsize}{operations/assets/222f51ab73e5595a18737b46972475327f0b1fc0.png}
				}
			\fi

As pointed out earlier, the values used for the actual scoring outlined in the \emphasis{HCM} are not necessarily internationally applicable. However, the methodology provides a framework within which calibration for local conditions is possible. The operational requirements for pedestrians vary significantly from hot-dry or hot-humid climates to cold climates. In hot-dry climates, the availability of shade is important, while in cold climates protection against the cold and wind is important. Such factors can be included in the pedestrian scoring and hence the LOS.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 154-159: code points 1-44

The bicycle and public transit level-of-service summarized below is only in terms of a score that is based on a weighted average cycling speed and\slash{}or public transit speed. The average cycling speed can be estimated by using the methodology outlined in the \emphasis{HCM} \emphasis{2010}, and depends on several variables such as bicycle and vehicle volumes, lane widths, number of vehicle lanes, heavy vehicles, and pavement conditions. The public transit average speed can also be estimated applying the \emphasis{HCM 2010} methodologies, and is dependent on, among other things, running speed, acceleration-deceleration delays, dwell times, reentry delay, as well as the pedestrian scores.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 161-167: code points 1-48

\tabletitle{3}{Bicycle and Transit LOS Criteria}
\label{chapter:traffic-impact-assessment:table:bicycle-and-transit-los-criteria}
\halign to 30\tablemodule{%
	\vtop{\sffamily\footnotesize\noindent\hsize=5\tablemodule#}\hbox to 0.5\tablemodule{}&
	\hbox to 0.5\tablemodule{}\vtop{\sffamily\footnotesize\noindent\hsize=24\tablemodule#}\cr
	\color{gray75}\bfseries LOS& \color{gray75}\bfseries LOS Score \cr
	\noalign{\vskip 1mm} \hline \noalign{\vskip 2mm} 
	\color{gray50}A&
	\color{gray50}<= 2.00\cr
	\noalign{\vskip 2mm 
}	\color{gray50}B&
	\color{gray50}> 2.00-2.75\cr
	\noalign{\vskip 2mm 
}	\color{gray50}C&
	\color{gray50}> 2.75-3.50\cr
	\noalign{\vskip 2mm 
}	\color{gray50}D&
	\color{gray50}> 3.50-4.25\cr
	\noalign{\vskip 2mm 
}	\color{gray50}E&
	\color{gray50}> 4.25-5.00\cr
	\noalign{\vskip 2mm 
}	\color{gray50}F&
	\color{gray50}> 5.00\cr
	\noalign{\vskip 2mm 
}}
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 170-192: code points 1-9

Source: Highway Capacity Manual, 2010.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 194-194: code points 1-38

Similar to the analysis for pedestrians, the local conditions related to cyclist operations can vary among different countries, depending on the local climate, the prevalence of the mode, and the mindset of motorists toward other mode users. The proposed methodology should be calibrated for local conditions.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 196-198: code points 1-105

The methodology provides a tool that can be used to compare routes based on the operation of all modes. The impact assessment should focus on all modes, and not just the public transit mode or the automobile mode.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 200-202: code points 1-5

What is often overlooked and not always explicitly considered in analysis methodologies and impact-assessment tools is the positive impact of the removal of existing public transit vehicles from mixed-traffic lanes in a corridor. This invariably results in a reduction in bus and general traffic volumes and even a possible increase in capacity along a route. Formal and informal bus and paratransit operations not only tend to stop in one or more curb lanes, blocking the lane for the duration of the stop, but also frequently merge and weave at will through the mixed-traffic lanes. The stopping and weaving movements have a negative impact on the capacity of the operations along a roadway facility. This behavior negatively impacts the automobile stream, and also negatively impacts transit customer safety and comfort, as well as cyclist and pedestrian safety and comfort.\par
% @ guide/08-traffic-impact-assessment/86-methodologies-and-performance-measures.src: lines 204-213: code points 1-0

\section{7}{Mitigation}
\label{volume:operations:chapter:traffic-impact-assessment:section:mitigation}
% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 2-67: code points 1-0

\quotation{You can never protect yourself 100\%. What you do is protect yourself as much as possible and mitigate risk to an acceptable degree. You can never remove all risk.}{Kevin Mitnick, consultant, 1963-}
% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 4-5: code points 1-34

From the detailed engineering analyses, transportation engineers will be able to estimate the impacts BRT will have on all modes, based on standard practice and\slash{}or the methods outlined above. The impacts essentially will depend on:\par
% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 7-9: code points 1-27

\begin{itemize}
\item The amount of actual road space available to mixed traffic, including private vehicles, general public transit vehicles, and commercial vehicles;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 11-13: code points 1-0
\item The extent of the space available for pedestrians and cyclists;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 13-14: code points 1-0
\item The extent of road space that will be created for the BRT services;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 14-15: code points 1-0
\item The time constraints at intersections where the different modes mix and or cross;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 15-16: code points 1-0
\item The capacity constraints at bottlenecks in the system.% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 16-16: code points 1-60
\end{itemize}
% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 11-16: code points 1-60

The illustration below presents a typical summary of such an analysis of a part of a BRT corridor. A summary is provided of the existing situation as well as the expected future situation with and without proposed mitigation measures.\par
% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 18-20: code points 1-29

\ifxetex
	% disabled for now
\else
	{  % group required to avoid fignote settings escaping
		\img{\hsize}{operations/assets/88bbeab637a9d42198b0d3a4e2779b3c9dc807fb.png}
		\fignote{3}{Example of recommended improvements.\label{chapter:traffic-impact-assessment:figure:example-of-recommended-improvements}}{ITS Engineers.}
	}
\fi

Defining impacts and the associated mitigation measures are closely linked to the expected future demand on the system, which depends to a large extent on the future mixed-traffic demand. In corridors where BRT has been successfully implemented, a reduction in general traffic demand often materializes. The reduced general traffic demand often negates the need for significant geometric improvements, such as adding more lanes. As pointed out earlier, the reduction in traffic demand is not always easy to estimate. Therefore, a practical approach to most impact assessments should be the evaluation of different scenarios based on different travel-demand estimates. The scenario analysis should present operators and decision makers with sufficient clarity on the possible impacts under different future demand scenarios. This applies specifically to the mode-shift scenarios from private vehicles to the BRT system.\par
% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 24-32: code points 1-89

Typical mitigation measures that could be considered along a corridor include the following:\par
% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 34-34: code points 1-92

\begin{itemize}
\item Removing on-street parking in order to maintain capacity for mixed traffic;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 36-37: code points 1-0
\item Improving channelization and the separation of modes;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 37-38: code points 1-0
\item Increasing the length of turning lanes to accommodate the design queues;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 38-39: code points 1-0
\item Increasing the number of lanes by widening the roadway at stations and intersections. Lane widths must not be wide enough to encourage speeding;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 39-41: code points 1-0
\item Reducing the number of signal phases by restricting low-volume turning movements;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 41-42: code points 1-0
\item Increasing the enforcement of street-vendor activities that might have an impact on transport capacity;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 42-44: code points 1-0
\item Implementing sidewalks and bicycle lanes alongside the BRT route, either on the same street or in a parallel corridor. This can often assist in improving the modal shift from an automobile to BRT and\slash{}or walk and cycling;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 44-47: code points 1-0
\item Banning turning movements at priority-controlled intersections and forcing drivers to make right turns instead of left turns (when driving on the right) or left turns instead of right turns (when driving on the left);% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 47-50: code points 1-0
\item Implementing median islands to prevent unnecessary turning movements and providing shelter for pedestrians;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 50-52: code points 1-0
\item Various signalization strategies to either benefit public transit vehicles and\slash{}or to improve the regulation of normal automobile traffic;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 52-54: code points 1-0
\item In extreme cases, the implementation of grade separation of vehicles and\slash{}or pedestrians might be necessary;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 54-56: code points 1-0
\item Consider parking areas near outlying BRT stations to allow park-and-ride. Parking areas could have negative land use impacts, specifically when compared to transit-oriented development, and should be considered with care;% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 56-59: code points 1-0
\item The BRT should always be considered as a mitigation measure in itself. It provides additional capacity along the corridor and provides an alternative mode for commuters, which will be more affordable than travelling by private car, at least as safe and possibly more comfortable, and with at least the same travel time as a car.% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 59-62: code points 1-26
\end{itemize}
% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 36-62: code points 1-26

The implementation of a BRT system immediately emphasizes the NMT modes, since customers need to travel to\slash{}from the stations. Therefore, as a general rule, pedestrian and cycling space should be provided in and along the BRT corridors as much as possible, specifically where many short trips are being served.\par
% @ guide/08-traffic-impact-assessment/87-mitigation.src: lines 64-67: code points 1-0

