Cell transmission model based variable speed limit control for freeways

摘要

Variable speed limit (VSL) can be used on freeways to manage traffic flow with the goal of improving capacity. To achieve the objective, this study proposes a novel VSL control strategy that explicitly considers the fundamental diagrams (FDs) at active bottleneck, and its upstream-downstream segments. To deeply understand the effectiveness of the VSL control, an analytical model based on the cell transmission model (CTM) is developed. Two modifications in the FD are proposed to model: (1) active bottleneck in which there is a capacity drop once feeding flow exceeds its capacity; and (2) variable free-flow speeds for the cells operated with VSL control. To allow these modifications, the local demand-supply approach is adopted to change the boundary condition of the CTM. As part of the VSL control algorithm, the proposed VSL control model is implemented in a North American urban freeway corridor with the model predictive control approach. This simulation study reveals that, in terms of traffic mobility, VSL is mostly effective during congestion periods.