Inputs

Input Volumes & Routing

For vehicle inputs, the consultant should include hourly flow rates in 15-minute intervals, except for the seeding period where a single time interval can be adjusted as appropriate. The consultant may need to vary the 15-minute input values according to the peak hour factor or based on the variation in the collected volume counts.

Static routes should typically extend through the length of the model. In general, it is not realistic to assume that vehicles make new decisions in short increments. If necessary, the consultant can use routing breaks only for locations when the signal spacing in conducive (e.g., signal spacing is close to a mile). The consultant can, at times, break routing at the freeway ramps, but both the freeway and arterial routing should be continuous. The consultant should consider separate routing decisions for heavy vehicles, if 1) their travel patterns do not match those of passenger vehicles or 2) if there are high occupancy vehicle (HOV) lanes in the model. The consultant should coordinate with UDOT Traffic Management Division if deviating from this routing methodology. 

The consultant should always input vehicle routing as hourly flows rather than as percentages, and the consultant should verify that pedestrians are included in the traffic counts and in the Vissim models.

Other Inputs

While Vissim has several other input variables that can be modified based on project needs, the consultant should generally use the default values from the UDOT template. The consultant should discuss changes with UDOT and fully document the modifications and reasons why the changes are needed.