Calibration of VISSIM models at three-legged unsignalized intersections under mixed traffic conditions

Unsignalized intersections in most of the developing countries do not have stringent traffic regulations causing frequent priority rule violations. Moreover, roads in such countries carry mixed traffic with wide variation in dimensional and operational characteristics of vehicles. Microsimulation has been used in several studies to model mixed traffic behavior. However, such studies are majorly limited to arterial roads and signalized intersections. The present study proposes a methodology for calibrating microsimulation models at unsignalized intersections where traffic is mixed and explicit priority rules are absent. Three unsignalized three-legged intersections were modeled in Verkehr in Staedten Simulation (VISSIM), a widely used microscopic traffic simulation software. Sensitivity analysis was performed to identify the calibration parameters, and the optimum values for these parameters were determined by minimizing the error between simulated and field traffic flow using trial-and-error approach. The calibrated simulation models were then validated using traffic flow and occupancy time as the measure of effectiveness. The calibration and validation were performed on a localized as well as global basis. The calibration and validation errors were found to be within acceptable limits (15%), indicating that the models can reliably simulate unsignalized intersections with reasonable accuracy.