Mitigating Expressway Work Zone Congestion and Off-Ramp Queue Spillover via Coordinated Ramp Metering and Variable Speed Limit

Work zones and off-ramp queue spillback are two major bottlenecks on expressways in developed urban areas. However, to our best knowledge, few studies have addressed these two types of bottlenecks simultaneously in expressway traffic control. This paper proposes a coordinated ramp metering and variable speed limit strategy to jointly mitigate work zone congestion and off-ramp queue spillover. A model predictive control framework, consisting of a traffic evolution module and an optimization module, is developed to update optimal control actions in a rolling-horizon manner. The traffic evolution module captures fixed lane drops caused by work zones and predicts dynamic lane drops induced by off-ramp queue spillback. The optimization module incorporates on- and off-ramp storage capacity constraints and designs a hierarchical penalty structure to proactively suppress queue spillover risks. A case study based on a congested urban expressway located in the central urban area of Shanghai is conducted to evaluate the proposed strategy. Results show that the proposed approach effectively mitigates work zone congestion and prevents on-ramp and off-ramp queue spillover. Compared with the no-control scenario, a 23.4% reduction in total time spent is achieved, outperforming traditional coordinated control strategies that neglect off-ramp queue dynamics.