Trip-Based Model

Existing Travel Demand Model


Trip Based Model Banner Image

Primary Purpose

The Regional Travel Demand Model provides travel forecasting capabilities for the analysis of SCAG’s plans and programs. The current trip-based model was developed and adopted for the 2012 Regional Transportation Plan/Sustainable Communities Strategy (RTP/SCS) analysis.

About the Trip Based Model

Network based transportation modeling is a mandated Federal Conformity Rules requirement. The trip-based model was Peer Reviewed in May 2011 and found consistent with the state-of-the-practice. Currently, this model is the only approved model for regional transportation plans and programs analysis within the SCAG Region.


SCAG’s trip-based model includes a very advanced mode choice component capable of forecasting all travel modes within the Region, including high-speed rail. Additional capabilities have been added to capture pricing and the travel effects of smart growth.


The model runs on the TransCad software platform and is based on a four-step model structure, which includes trip generation, trip distribution, mode choice, and trip assignment.

Inputs & Outputs

  • Transportation Analysis Zones (TAZs) (4,109 tier 1 zones, 11,267 tier 2 zones)
  • Socioeconomic Data (population, employment, households, workers, school enrollment)
  • Highway network (70,000+ street segments, posted speed, number of lanes, and functional classification)
  • Transit network (2000+ routes/patterns, headway, service hours, fares, stop locations)
  • Seaports (heavy duty trucks)
  • Airports (passenger and cargo trips)
  • External (interaction with other regions and pass-through trips)
  • Vehicle trips
  • Traffic volumes
  • VMT by link and geographic areas
  • Trips origin/destination
  • Trip length
  • Mode shares
  • Transit boarding


SCAG Regional Travel Demand Model and 2012 Model Validation