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Objective

Software implementations of the Highway Capacity Manual are suitable for obtaining post-processed speeds from traffic forecasts. However, traffic microsimulations may be used to provide much more refined outputs of speeds and travel times in and near a highway project with unusual geometry or complicated arrangements of traffic controls. True hybrid models, which involve traffic microsimulations, are discussed in Multi-resolution models. Speed and travel time refinements are described in Refining speeds for evaluation.

Traffic microsimulations are considered superior to travel models in their estimates of delays, but microsimulations may be costly. It is important that any traffic microsimulation be set up such that turning movements are identical to the traffic forecast. Since results from traffic microsimulations vary from run to run, it is important to repeat any given simulation several times with different random seeds.

Traffic microsimulations can provide other indicators of traffic performance, such as queue lengths, and microsimulations can precisely pinpoint the location of potential traffic problems. Traffic microsimulations can also provide a good evaluation of the suitability of specific traffic controls.

List of Acceptable Traffic Analysis/Microsimulation Software

Agencies are encouraged to develop a list of acceptable software packages for post-processing results from a traffic forecast. Software documentation should be consulted for the proper use of each product and the interpretation of the product’s outputs.

References