Comparison of Simulation Modules of TRANSYT and INTEGRATION Models

Abstract

The TRANSYT simulation/optimization model serves as an unofficial international standard against which many measure the efficiency of other methods of coordinating networks of traffic signals that operate at a constant and common cycle length. However, dynamics due to traffic rerouting, the simultaneous operation of adjacent traffic signals at different cycle lengths, the effect of queue spillbacks on the capacity of upstream links, and various forms of real-time intersection control cannot be modeled using a static model such as TRANSYT. This has created a unique niche for a more dynamic signal network simulation tool. Before modeling such special dynamic scenarios, there first exists a need to validate the static signal control features of such a model and to determine if its unique dynamic features still permit it to yield credible static results. This study has two objectives. First, it attempts to illustrate the extent to which estimates of vehicle travel time, vehicle delay, and number of vehicle stops are related when a standard static signal network is examined using both TRANSYT and INTEGRATION. Second, it strives to illustrate that the types of more complex signal timing problems, which at present cannot be examined by the TRANSYT model, can be examined using the dynamic features of INTEGRATION. The results are intended to permit a better appreciation of both their differences and similarities and permit a more informed decision as to when and where each model should be used. Also demonstrated is that INTEGRATION simulates traffic-signalized networks in a manner that is consistent with TRANSYT for conditions in which TRANSYT is valid. Specifically, the difference in total travel time and percentage of vehicle stops is within 5 percent. In addition, it is also shown that INTEGRATION can simulate conditions that represent the limitations to the current TRANSYT model, such as degrees of saturation in excess of 95 percent and adjacent signals operating at different cycle length durations. This analysis of the simulation features of TRANSYT and INTEGRATION is intended to be a precursor to a comparison of their respective optimization routines.