Although the TRANSYT traffic model simulates transit vehicles in mixed traffic operation, it does not adequately consider the effects of bus or streetcar stops on the travelled roadway near signalised intersections. Specifically, it assumes that transit vehicles loading and unloading passengers do not delay other vehicles. This reduces the validity of TRANSYT evaluations for cycles in which buses stop at or very near signalised intersections. The overall TRANSYT predictions and optimisations for an average cycle will be seriously threatened if total bus or streetcar dwell time per hour is significant. Therefore, an alternative type of network formulation, which uses dummy nodes and dummy links with appropriate link costs, is proposed for modelling the effects of transit stops on intersection performance. Although it requires one dummy node and four or six dummy links for each transit stop that delays traffic, it significantly improves TRANSYT's realism for such operations. Parameters for these dummy links have been tested over a wide range, and a set of operational values is recommended. Flow profiles illustrating the need for the effects of the recommended formulation are presented in this paper.
Abstract