Modeling Traffic Congestion Using Simulation Software

Traffic simulations are being increasingly utilized as transportation systems have become more complex and congested. However, most simulation models have limitations in overcapacity demand conditions. When traffic in a congested area "fills" the available roadway space additional traffic demand may never be allowed to enter the network. The intent of this paper is to explore one possible means to address the issue of unserved vehicles in overcapacity conditions using the VISSIM trip chain. The VISSIM trip chain feature is used for this analysis as it has the advantage of not eliminating a vehicle when congestion hinders its entrance onto a network, instead holding the vehicle until an acceptable gap exists on the entry link. A sample network is built to investigate the difference between standard traffic flow inputs and the trip chain method in overcapacity conditions. Also, simulations with different minimum space headway parameters in the priority rules are analyzed, allowing for an initial investigation into the sensitivity of the model to this parameter. Based on the analysis conducted it is concluded that, with appropriate calibrations, the trip chain feature in VISSIM is a potentially useful method to provide realistic modeling of various overcapacity conditions.