With Release 7.3, the Freeways module now models travel time reliability for Travel Time Index and Reliability Rating by analyzing hundreds of scenarios for the variance of demand, weather, incidents, work zones, and special events over time.
Freeway facility reliability analyses evaluate the travel time reliability experiences of motorists on an urban or rural freeway facility. Travel time reliability reflects the distribution of trip travel time over an extended period of time. The distribution arises from the occurrence of a number of factors that influence travel time. The distribution describes how often these factors occur and how severely operations are impacted as a result. The methodology of the application uses the HCM Chapters 11 and 25 procedures.
The general workflow for performing a freeway facility travel time reliability analysis is as follows:
- select a base freeway file
- specify the reliability reporting period
- select the weather location closest to the facility
- specify freeway area type as urban or rural and the base file traffic count data
- input the incident/crash frequency data if available and specify work zone events if any.
After performing the above steps, depending on the selected analysis duration, several scenarios are automatically generated typically within a few seconds. The Events and Summary screens show the descriptions of the generated events and scenarios. Each of these individual scenario files can be independently opened in the Freeways module for further analysis. Finally, the Report page shows a formatted report and a text report option. The formatted report displays travel time distribution graphs.