New Methodology for Development of Regional Vehicle-Mapping Tables for MOBILE Emissions Model

Among the many input factors to the MOBILE emissions model, vehicle miles traveled (VMT) fractions (the percentage of VMT for different types of vehicles by roadway functional classes) plays an important role because different types of vehicles produce emissions at different rates. In addition, since the vehicle classification scheme of MOBILE is different from the FHWA vehicle types used in traffic data collection, a vehicle-mapping table that converts VMT fractions from FHWA types to MOBILE types deserves special attention. The research described in this paper produced a new methodology to develop a vehicle-mapping table by using readily available data sources, namely, (a) vehicle registration data from the Department of Motor Vehicles of Virginia and (b) Vehicle Inventory and Use Survey data from the Bureau of the Census. To evaluate the new methodology, a vehicle-mapping table for Virginia was developed and then compared with three commonly used mapping-table methodologies. In addition, on the basis of the four vehicle-mapping tables, VMT fractions, emissions rates, and final emissions for the Hampton Roads region of Virginia were estimated. An analysis of the results illustrates that use of the proposed mapping-table development methodology affects VMT fraction estimates. In turn, the VMT fraction estimates result in significant differences in the emissions rate estimates generated by the MOBILE model.