A multiple user class equilibrium assignment algorithm is formulated to determine vehicle trips and the vehicle miles of travel (VMT) in various operating modes on highway links. A heuristic solution algorithm based on the Frank-Wolfe decomposition of the equilibrium assignment problem is presented. The treatment of intrazonal trips, which are very important for emission studies, is also discussed. The solution algorithm is implemented in a traffic assignment program for emission studies, referred to as TAPES. The use of the algorithm is demonstrated through a TAPES model case study on a Charlotte, NC network database for 1990 AM peak period. The operating mode mix of VMT in cold transient, hot transient and hot stabilized modes, also known as the mix of cold-starts, hot-starts and stabilized mode trips, is derived on a link by link basis. The results are aggregated by facility type and the location of link segments. It is observed that the operating mode fractions in transient and stabilized modes could vary widely across different facility types geographic locations. The aggregated operating mode fractions derived from the assignment analysis indicates that a lesser proportion of VMT operates in cold and hot transient modes when compared to the operating mode mix derived from the Federal Test Procedure (FTP).
Abstract