Alternative Methodology for Collecting Local Vehicle Start Information for Use in MOBILE6

Abstract

MOBILE is the regulatory model of emissions factors from mobile sources that the Environmental Protection Agency (EPA) requires all states except California to use in developing emissions inventories and performing conformity analyses. The agency released the latest version of the model, MOBILE6, early in 2002. It is dramatically different from previous versions of the model and allows users to provide local input data for new and revised variables. It also includes a mechanism for producing separate start emissions rates by hour of the day and vehicle class. The default data are based primarily on start data collected from a series of instrumented vehicle studies in two metropolitan areas. However, EPA explicitly warns of the limitations such “national averages” can have on effectively representing individual metropolitan areas. Finally, the resources used to acquire the default data may not be readily available to, or economically feasible for, many metropolitan planning organizations. An alternative procedure for collecting vehicle start profile data and a preliminary comparison of these profiles to the default values proposed for MOBILE6 are presented. Profiles representing vehicle start characteristics in Knoxville, Tennessee, were developed from collected data. The method of data collection varied considerably from EPA’s practices yet produced comparable results. The profiles developed were compared with EPA default data, and preliminary results indicate that the Knoxville profiles for average starts per day per vehicle were somewhat lower than the default “national average” values included in MOBILE6. Although the profiles for daily distribution of vehicle starts followed the general pattern of MOBILE6 default data, some differences were found.