One key impediment to promoting transportation demand management (TDM) programs as measures to improve air quality has been the difficulty in quantifying benefits--specifically, the lack of quantification tools accessible to the nonspecialists who are responsible for implementing TDM programs in local government and in workplaces. To address this issue, the Environmental Protection Agency (EPA), supported by Sierra Research, Inc., developed a user-friendly spreadsheet-based model called COMMUTER to calculate the travel and air quality benefits of programs that encourage commuter travel modes other than solo driving. The model assesses the benefits of measures that provide information about and encouragement to use alternative modes other than in-vehicle travel time for automotive modes. Hence COMMUTER does not estimate roadway pricing, the impacts of roadway expansions, signalization improvements, and the like. It uses a pivot-point method to estimate changes in trips and vehicle miles of travel from baseline conditions and a lookup table of emissions factors from EPA's MOBILE model to estimate the resulting emissions changes. The model uses key shortcuts in the amount of data used and the number of microlevel calculations performed to judiciously trade off some accuracy for a significant increase in ease of use. Regional analyses can be performed on programs covering defined subregions within an urban area, such as a central business district or a highly traveled corridor. Site-specific analyses enable benefits to be projected for programs at individual work sites.
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