A network assignment based approach to modeling mobile source emissions

This study proposes a methodology to determine alternative operating mode fractions to the outdated operating mode mix derived from the Federal Test Procedure (FTP) driving cycle. The Nationwide Personal Transportation Survey (NPTS) data were analyzed to determine operating modes of vehicles at trip origins and destinations. The chain of all trips made by each vehicle in a household were identified to conduct a soak time distribution analysis and to determine the operating modes at trip origins. The start mode analysis was performed for different trip purposes. The information on travel time and vehicle miles of travel were analyzed to determine areawide operating mode fractions.; It was observed that the start modes at trip origins and destinations vary not only by time-of-day but also by trip purpose. The operating mode fractions developed from the NPTS data analysis indicated that the proportion of vehicle miles of travel (VMT) in cold transient mode are underestimated and the VMT in the hot transient mode are overestimated by the FTP mode mix.; A specialized traffic assignment program called TAPES (for Traffic Assignment Program for Emission Studies) was developed for the purpose of tracing cold and hot start trips up to a threshold at which they operate in the stabilized mode. An application of the assignment technique was demonstrated using the transportation planning network for Charlotte, NC. It was observed that the operating mode fractions in transient and stabilized modes could vary widely across different facility types and geographic locations. Based on a comparison of operating mode fractions derived from the FTP driving cycle, NPTS data analysis and the Charlotte case study demonstration, a set of guidelines were recommended for using these operating mode fractions in emission inventory studies.; For a coarse area wide emission inventory study, operating mode fractions derived from the NPTS data analysis are recommended. For detailed corridor oriented and high resolution emission inventory studies, it is recommended that a specialized traffic assignment analysis be conducted using TAPES for deriving micro-scale (on individual network links) operating mode fractions.