ALTERNATIVE OPERATING MODE FRACTIONS TO FEDERAL TEST PROCEDURE MODE MIX FOR MOBILE SOURCE EMISSIONS MODELING

An emission inventory is a key component of an air quality control program. The emission rates of carbon monoxide and hydrocarbons are sensitive to the variations in the inputs related to cold transient, hot transient, and hot stabilized operating mode fractions. Therefore it is important to provide realistic values for these parameters while modeling emissions using air quality models such as the MOBILE model. The objective of the research presented is to derive aggregate operating mode fractions as alternatives to the federal test procedure (FTP) mode mix on the basis of a detailed analysis of personal travel data. The data source used for the analysis of personal travel information is the 1990 Nationwide Personal Travel Survey. Issues related to data quality, screening, and aggregation are discussed. After determining of the percentages of start mode as cold starts and hot starts, the percentages of vehicle miles of travel (VMT) operating in different modes are derived by trip purpose and for different time periods. The VMT weighted operating mode fractions derived from these start mode fractions indicated a significant difference from the FTP operating mode mix. It is observed that the FTP operating mode mix generally underestimates the portion of travel in cold transient mode. Also, it is observed that the percentage of VMT in cold transient mode decreases with the increase in the size of the urban area.