Using Variable Speed Limits to Reduce Rear-End Collision Risks Near Recurrent Bottlenecks

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Zhibin Li
Pan Liu
John M. Bigham
David R. Ragland

Rear-end collisions would occur if vehicle speeds decrease abruptly when encountering kinematic waves (KWs) emanating from active bottlenecks. This study aims to develop a control strategy in variable speed limits (VSL) to reduce rear-end collision risks near recurrent bottlenecks. Using the crash prediction model developed for rear-end collisions related to risky KWs, the effectiveness of VSL control strategies were evaluated in the cell transmission model (CTM). Several strategies were tested in sequence to determine the best case for risk reduction. Results of this study show that the collision risk can be effectively reduced if the speed limit is lowered in an opportune occasion. The VSL needs to response quickly to the fast changing traffic condition while should simultaneously avoid the potential disturbance to the traffic. According to the simulation results, the following recommendations are made when implementing the VSL to improve safety situation near recurrent bottlenecks: moderate threshold of collision likelihood to active VSL, moderate design speed limit in VSL, fast speed change over time, and small speed difference between consecutive VSLs.

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