Variable Speed Limit Systems: Safety and Operational Impacts for Freeways Applications

A candidate Variable Speed Limits Sign (VSLS) control algorithm was applied to an urban freeway in Toronto, Canada using microsimulation. The microsimulation model was combined with a categorical crash model to quantify the impacts of VSLS implementation on safety and traffic performance. The VSLS control strategy was developed as a practical algorithm that responded to real-time measures of traffic conditions. Evaluation of the VSLS impacts revealed that the control strategy could produce desirable impacts (i.e. reduced crash potential associated with a small travel time penalty) but only for a limited range of traffic conditions. Modifications to the algorithm parameters revealed that considerable improvements to the original results could be achieved. The travel time penalty was significantly reduced while a high reduction in crash potential was maintained.