Case Study:

Sacramento, California

Methodology

Calculation of Emissions

The California Air Resources Board's EMFAC7F model was used to develop vehicle emission factors, and The California Department of Transportation's Direct Travel Impact Model 2 (DTIM2) was used to simulate the emissions effects of scenarios. Travel model outputs from the a.m. peak, p.m. peak, and off-peak periods were used in conjunction with regional cold start and hot start coefficients for each hour in a 24-hour summer day, as provided by SACOG.

For metropolitan areas outside California performing a similar analysis, emission factors from the EPA's MOBILE model could be used. The MOBILE6 model, to be released in 2000, will provide the advantage over MOBILE5 that it will explicitly model emissions from starts as well as VMT (the California models already have this capability). This can be important because different scenarios may have different effects on the number of trips vs. trip lengths. A transit scenario without transit-oriented development, for example, may cause a larger decrease in VMT than trips, since many people will access the transit system via a car trip.

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