8.4Level of Analysis

The analysis of the thing is not the thing itself.Aaron Allston, novelist, 1960–2014

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 Planning Level, to an Operational Analysis, and down to a very detailed 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/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:

• 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/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;
• Operational Analysis: 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/or the relevant authorities. However, where additional detail is required for complex intersections or networks, a Microscopic Simulation will be necessary;
• Microscopic Simulation: This involves the computer simulation of the behavior and movement of individual vehicles, bicycles, and/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.