Examining the effectiveness of variable speed limit from a long-term equilibrium perspective with empirical data

This paper examines the effectiveness of variable speed limits (VSLs) on improving traffic flow efficiency in a stylized setting of morning commute where a fixed number of individuals commute from home to work through a single bottleneck. We consider a VSL system installed along the freeway towards the bottleneck, which adjusts commuters' cruising speeds in a discrete fashion and essentially regulates the upstream flow into the bottleneck. By investigating the departure-time equilibrium under the proposed VSL system, we establish conditions for the system to improve various performance measures and bound its efficiency. Based on empirical data, we conclude that the proposed VSL system can avoid or delay capacity drop associated with an active bottleneck and thus reduce queuing delay. It can help reduce the schedule delay cost. However, it is unlikely for the VSL system to reduce total travel time, individual travel cost in this particular setting.