SCAG Transportation Demand Model

SCAG by federal mandate is required to maintain two major planning documents: the Regional Transportation Plan and the Regional Transportation Improvement Plan. These two plans and other SCAG transportation studies rely heavily on the Transportation Demand Model for predicting the impact of travel growth and evaluating potential transportation improvements.

The Transportation Demand Model comprises a large number of data files in order to represent the many facets of the transportation environment. These data sets provide assumptions on population, employment, income, roadway and transit networks and transportation costs. Using this data the model estimates:

  • Traffic congestion (Highway level-of-service)
  • Freight traffic (heavy duty trucks)
  • Passengers riding existing and future transit services
  • Smog caused by automotive emissions

SCAG's transportation demand model is similar to models used by other transportation planning agencies nationwide. All such models divide analysis into in four stages:

  • Trip Generation (How often to people travel? How many workers are drawn to any give
    employment center?)
  • Trip Distribution (Where do persons travel to work, school or shopping)
  • Mode Choice (How many persons drive alone, share a ride or take transit?)
  • Trip Assignment (What routes do travelers use and how much congestion results?)