Transportation Modeling

Models are important tools in the transportation planning process.  Travel demand forecasting models can simulate traffic levels and travel patterns for a specific geographic area.  The model’s output includes projections of traffic volumes on major roads and important metrics needed for emissions forecasts and environmental impact analysis, such as vehicle miles of travel (VMT).

MCAG uses a travel demand forecasting model to prepare long-range transportation planning studies, like the Regional Transportation Plan. This will provide MCAG with the information needed to forecast potential future scenarios of where people will live, work and travel and to plan accordingly with appropriate resources.  It is also used to analyze the impact of regionally significant transportation projects on the transportation system.

About MCAG'S Travel Demand Forecasting Model

The MCAG model has been calibrated and validated to 2015 base year conditions using observed traffic counts, census data travel survey estimates, and land use data.

The model is consistent in form and function with standard travel forecasting models used in transportation planning. The model includes a land-use based trip generation module, a gravity-based trip distribution model, a capacity-constrained equilibrium traffic assignment process, and a simplified mode choice component that estimates transit, walk, and bike trips and generates auto trips for drive alone, shared ride with two people, and shared ride with three or more people. 

The model uses Version 6.4.3 with GIS of the Citilabs Cube Voyager transportation planning software, which is consistent with many of the models used by local jurisdictions in California and throughout the nation.  

The model area encompasses Merced County. To represent travel into and out of Merced County, the model also includes 20 “external gateways” at major roads that cross the county line.  San Joaquin and Stanislaus counties were removed to better reflect the changes of land use and travel choices within Merced County.

Limitations

The MCAG model has been developed for regional planning purposes within a trip-based model framework. The model conforms to the recommendations outlined in the 2017 California Regional Transportation Guidelines for Group B2 metropolitan planning organization (MPO) but does have limitations.

  • The current structure has limited sensitivity to factors that may affect trip generation rates such as significant declines in economic activity. (e.g., COVID-19 effects). However, since the model has a land use occupancy component, economic cycles can be reflected in the assumed intensity of land uses within the model.
  • Although the model network includes all local roadways, not all local roadways are assigned vehicle trips. Use of the model for local applications will require sub-area refinements and validation to ensure the model is appropriately sensitive to changes at this scale.
  • Model parameters relying on household travel survey data are based on a small sample size. Future model updates would benefit from a larger sample of households in Merced County.
  • The trip-based model structure does not allow for complete estimates of forecasts of vehicle trips (VT) or vehicle miles traveled (VMT) generated by residential households or individual persons. Vehicle trips are assigned at the TAZ level and any connection to individual land uses that originally generated the trips are lost. VT and VMT can be expressed as ratios such as VMT per capita or VMT per household. But these ratios are based only on dividing total VMT by the number of people or households in the model area. It does not indicate the level of VT or VMT being generated.
  • Although the model passes reasonableness checks, and static and dynamic validation, it is recommended that the model be validated in the study area before it used for local-scale projects. This is especially important in the near-term during the recovery after the pandemic, since land use development and travel patterns may change significantly.

MCAG’s Travel Demand Model Resources

Model Development Report

Model User’s Guide 

How to request data files:

For access to MCAG’s Travel Demand Model, please fill out the Data Request Form and return to Elizabeth.forte@mcagov.org.

Also check out MCAG’s Open Data Hub for readily available GIS layers.