Combined Ramp-Metering and Variable Speed Limit System for Capacity Drop Control at Merge Bottlenecks

This paper proposes a ramp metering and variable speed limit (RM-VSL) control strategy to prevent and recover from capacity drop at freeway merge bottlenecks. Using bounded acceleration kinematic wave theory, we propose a strategy designed to prevent disruptive lane-changing maneuvers at the merge that cause capacity drop. This strategy gives more flexibility to control the ramp queue length by transferring some congestion to the freeway while maximizing total system discharge rate. Simulation experiments showed that the proposed RM-VSL system outperforms both individual components in isolation for preventing or curtailing traffic breakdown. The proposed strategy can be implemented with current technology.