University of California Transportation Center

After describing the current emission modeling regime, the paper identifies and discusses the major problems with the existing emission modeling approaches. The current short-term modeling improvement programs of the US Environmental Protection Agency and the California Air Resources Board are discussed. The paper then outlines the three long-term modeling improvement approaches that are currently being investigated by regulatory agencies: a multiple-cycle method, an engine map approach, and a modal modeling technique. Finally, the vehicle activity and emission rate data needs for each modeling approach (both for model development and implementation) are described.