Modeling

Overview

SACOG Travel Demand Model

To make plans that will shape how people will live, work, and play, we need to understand how people travel today and think about how they will travel in the future. SACOG uses the travel demand model to understand how people move and the information gained from the models help create plans for the future. 

What is SACOG’s travel demand model?

SACOG’s travel demand model, known as SACSIM, predicts how people in the six-county SACOG region travel on a typical weekday, including where they go, when they make trips, why they make trips, what travel mode or modes they use, and much more.

Why does SACOG have a travel demand model?

Travel behavior predictions made using SACSIM are at the heart of some of the key policy questions SACOG tackles, including:

  • How are proposed investments in the transportation system likely to affect peoples’ travel habits and choices?
  • How will these changes in travel affect air quality, traffic congestion, and greenhouse gas emissions?
  • Which proposed projects show the greatest potential to further regional policy goals like reducing congestion, improving air quality, reducing greenhouse gas emissions, and promoting alternative modes of travel like cycling, walking, and public transportation?
  • How will planned development affect travel patterns in the region?
  • How will proposed projects and developments affect different communities, and in particular disadvantaged communities?

What information does the travel model use to predict travel behavior?

A rich array of input and reference data is used to develop, adjust, and maintain SACSIM. Some of the key sources are:

  • Survey data – Household travel surveys gather detailed information from a sample of the region’s population, including how they travel and what affects their travel choices.  SACOG completed a survey of 4,000 households in the region in 2018 and is using the results to help update SACSIM to better reflect current travel patterns. Other household travel surveys, like those conducted by periodically by the state or federal agencies, are also useful references.
  • American Community Survey (ACS) –  This is the best source of data on ongoing demographic changes in our region, like aging of the population, changes in income and worker status, etc.  ACS data are used to track these changes over time and help determine the demographic assumptions to be used in SACSIM. 
  • Transportation system data – detailed data on roads and highways, transit service, and bicycle and pedestrian facilities also go into the model. Data on system usage, like traffic counts on major roadways and transit ridership, are also used to validate SACSIM’s outputs.  Together, this system data ensures the model accurately represents the regional transportation in its present form while providing the ability to show what the transportation system would look like under different scenarios and project proposals.