TRIP-BASED APPROACH TO ESTIMATE EMISSIONS WITH ENVIRONMENTAL PROTECTION AGENCY'S MOBILE MODEL

Abstract

The Environmental Protection Agency's (EPA's) MOBILE model outputs an emission rate per vehicle mile of travel (VMT). The rate is based on the federal test procedure (FTP), which represents typical driving conditions for an urban vehicle trip. In current practice, however, links instead of trips are used to estimate both VMT and many of the travel characteristics needed as inputs to MOBILE. For example, average link speeds are provided as input to MOBILE in current practice, although trip speeds might be more appropriate, given the FTP basis of MOBILE emission factors. A different approach to application of emissions factors from MOBILE is presented. The approach is based on trips rather than on links and therefore more consistent with the trip basis used to develop MOBILE's emissions factors. The approach also allows development of data on travel characteristics from travel model output and travel survey data in a straightforward manner and does not require the special efforts to account for missing VMT needed in the link-based approach. However, its most important advantage over the link-based approach is that it facilitates estimation of impacts of transportation control measures on non-VMT MOBILE inputs such as cold-start percentages, vehicle mix, and trip length distribution.