The study limits for a project are determined during the scoping process. The study limits incorporate the project limits plus the area of influence, which have an impact on the operations in the study area. Wherever applicable, it is recommended that the model extends a minimum of one intersection or interchange both upstream and downstream of the farthest intersection or interchange within the study area.

Figure 13-1

below shows an

example

from the FHWA Interstate System Access Informational Guide of potential study limits on an interstate project

See

Section 13.6

of this chapter for more information about incorporating unmet demand into a microsimulation model. Preferably, travel speeds at the study limits remain near free-flow speeds throughout the analysis period. This allows the modeler to fully capture the formation and dissipation of congestion within the study area limits.

Study time periods are selected such that they include the time prior to the buildup of congestion and end after the dissipation of congestion. A simulation model is developed for a period of time that is necessary to replicate the full extent of congested traffic operations within the study area peak period or peak hour. For models that are oversaturated, the study period is typically expanded to include the buildup and dissipation of congestion. Otherwise, a peak hour analysis and seeding period (the initial time it takes for the model to represent real-world conditions) may be sufficient. The seeding period is typically at least twice the minimum amount of time that it takes one vehicle to traverse the longest extent of the network. The peak hour is defined as four consecutive 15-minute intervals of turning movement traffic count data that represents the highest traffic volume in an hour. A peak period consists of two or more hours, including the time segment when traffic demands are highest and traffic operations are typically sub-standard. Land use adjacent to the project is considered as it may impact not only the time when data is collected, but also which study time period to use.

As stated in

Chapter 4

of this manual, MOE provide information to decision makers on the performance of the microsimulation model and help determine similarities and differences between alternatives. These MOEs are projectand tool-specific but generally aim to quantify mobility, reliability, and accessibility. Modelers typically measure some or all of the following network MOEs while conducting a microsimulation analysis:

In addition to network MOEs, link MOEs are used if the results of specific roadway segments are of particular interest. MOEs for links include volume, density, speed, emissions, and relative delay. Add a caveat when reporting density directly from a microsimulation model since microsimulation tools have their own way of interpreting density while the HCM density is based on converting all vehicles to a passenger car equivalent. Network MOEs are also an output from some microsimulation models. These MOEs include environmental MOEs (total emissions released), total number of vehicles, average speed, total stops, average stops, fuel consumption, latent demand, total travel time, and total delay. These MOE types describe the results of the entire network rather than specific intersections or links. See

Chapter 4

for additional guidance on MOE selection.

Due to the complex and resource-intensive nature of microsimulation tools, carefully consider the tool based on project scope, project schedule, project type, needs, complexity, MOEs, and budget. There is often more than one suitable traffic analysis tool for a given project. Only use microsimulation when necessary.

Microsimulation is often used to analyze locations with the following characteristics: