Evaluating Reliability of TRANSYT-7F Optimization Schemes

Abstract

This paper investigates the reliability of TRANSYT-7F optimal solutions from two perspectives: (1) the effect of the selected optimization criterion on the values of various system performance measures; and (2) the extent to which TRANSYT-7F signal plans remain optimal when evaluated in a microscopic and stochastic traffic environment. The well-established CORSIM model was used for the latter test. A customized code has been developed that can automatically generate statistical distributions of selected performance measures in CORSIM based on various TRANSYT-7F optimization runs. The method has been applied to a calibrated test network in Chicago consisting of 9 signalized intersections with 50 nodes and 74 links. It was found that while good correlation existed between the corresponding performance measures in TRANSYT-7F and CORSIM under light traffic, their correlation diminished under congested flow. In particular, the best signal strategy identified in TRANSYT-7F was not the best in the CORSIM environment. The discrepancies are undoubtedly due to the basic difference between the two models: TRANSYT-7F is deterministic, CORSIM is stochastic.