Evaluation of the effects of variable message signs at urban traffic network

In the context of serious congestion in most metropolitan areas and the development of intelligent transportation technology, variable message signs (VMS), as a part of route guidance system, are developed to alleviate congestion via providing drivers real-time travel information. It is expected that by providing dynamic travel time to drivers, both the congestion in network and average individual cost will be reduced. So getting the knowledge of the efficiency of a VMS system is important to researchers and designers. In order to evaluate the effects of variable message signs at urban network, a simulation-based, time-dependent traffic assignment model is proposed in this paper. The model uses a cell-based network loading model and the Method of Successive Average algorithm to achieve stochastic user equilibrium at each sampling interval. A numerical example of the VMS system in Beijing is used to illustrate the effects of the variable message signs. The evaluation process is both based on network level and user level in situations of recurrent congestion and non-recurrent congestion. Finally a conclusion is drawn that the VMS system can alleviate congestion even if not all links in network are displayed by VMS.