Simulating Impacts of Variable Speed Limits on Traffic Safety on Freeways

To reduce the occurrence of rear-end collisions during the propagation of kinematic waves in freeway section upstream of a recurrent bottleneck, a simulation platform for variable speed limits (VSLs) was developed using the PARAMICS microscopic simulation model. The simulation network is a freeway section containing an on-ramp bottleneck. A crash prediction model was adopted to quantify the real-time rear-end collision risks accompanying the propagation of kinematic waves in the section upstream of the on-ramp bottleneck. Control strategies for VSLs were proposed to reduce the collision potential. Results show that the optimal strategy to reduce collision risk is that the startup threshold of collision probability is set to 0.25, time step for VSL change to 120 s, speed step for reduction to 20 km/h, speed step for recovery to 10 km/h, and difference between adjacent speed limit signs to 20 km/h. Using the optimal control strategy for VSLs, the rear-end collision risk in the freeway section upstream of the recurrent bottleneck is reduced by 20%.