Travel Demand Model Enhancements
Congestion pricing strategies for the study will be evaluated by using an enhanced version of the SCAG regional travel demand model. The current SCAG model has four separate steps to estimate travel patterns in the region.
Trip generation estimates the number of trips produced by each household or job
Trip distribution estimates where people will travel for work, shopping, etc.
Mode choice estimates how people will travel - by auto, carpool, bus, rail, etc.
Trip assignment allocates vehicular traffic to the highway network and person-trips to the transit network, based on optimum routing and within suitable time periods
Most of the steps were developed and calibrated to existing conditions, where most auto travel is not priced. Several enhancements were applied to the model to measure travel under priced conditions.
- Trip suppression or consolidation due to pricing is reflected in a new substep that is added immediately before trip assignment. This compares the added cost of travel for priced movements against changes in travel time for these movements to estimate the change in tripmaking that may take place in reaction to pricing. Reductions in tripmaking occur as people make fewer trips or combine multiple trips into one trip.
- Trip distribution and mode choice steps are merged into a combined "destination/mode choice" model that uses travel costs and other travel accessibility measures to compare the relative attractiveness of different zones.
- The time-of-day process that splits trips into different times of day is modified to consider travel delay and distance, among other factors, in travelers' choice of time of travel. This allows the model to estimate how travelers may shift back into the peak hours should pricing improve travel times in the peak hours.
