Case Study:

Sacramento, California

Methodology

Travel Demand Model

This study uses the 1996 Sacramento regional travel demand model (SACMET96). According to the study authors, the SACMET96 model includes a number of features that make it well-suited for modeling land use, transit, and pricing measures. Some of these features include:

• Feedback of travel impedances to the trip distribution step;

• Accessibility as a determinant of auto ownership and trip generation;

• A joint destination and mode choice model for work trips;

• A mode choice model with separate walk and bike modes, walk and drive transit access modes, and two carpool modes (two and three or more occupants);

• Land use, travel time and monetary costs, and household attribute variables included in the mode choice models;

• All mode choice equations in logit form; and

• A trip assignment step that includes separate a.m., p.m., and off-peak periods.

The mechanism for incorporating land use into the mode choice models is through a pedestrian environment factor (PEF). The PEF is a rating assigned to each zone based on how conducive that zone is to pedestrian travel. The rating is similar to that used in the Portland LUTRAQ study and is based on sidewalk availability, ease of street crossing, connectivity of the street/sidewalk system, and terrain. Additional documentation of the SACMET96 model can be found in DKS (1994).

The study authors also note that the SACMET96 model, like many travel demand models, contains a number of limitations that mean that not all transportation choices are fully sensitive to the range of policy options tested. For example:

• In the trip distribution step, non-work trips are sensitive only to travel time and not to travel cost;

• Time-of-day factors are applied after mode choice and, as a result, only the work trip purposes use peak or congested travel times during the trip distribution and mode choice steps;

• The trip assignment step is not directly sensitive to travel cost and only the home-based work trips use congested times. As a result, the models sensitivity to the HOT lanes and pricing policies is somewhat limited;

• Only the home-based work mode choice model uses three income groups; other mode choice models are not based on income groups, which restricts the sensitivity of the simulation;

• SACMET96 does not include a time-of-day choice model and cannot simulate the phenomenon known as peak spreading.

The Travel Model Improvement Program has identified short-term and long-term ways to enhance travel demand models to more accurately model a broader range of transportation investments and policies.

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