Coordination of Ramp Metering and Surface Road Signal Control to Concurrently Prevent On-Ramp Spillover and Enhance Freeway Traffic Flow

Ramp metering is a widely implemented strategy for managing freeway congestion; however, its effectiveness is often compromised by limited ramp storage capacity, which can cause queue spillback into adjacent signalized intersections and disrupt overall network performance. To address this issue, this study proposed a real-time coordinated ramp-arterial control (R-CRAC) system that synchronizes ramp metering with adjacent intersection signal timing control to prevent queue spillback and enhance freeway operations. The R-CRAC system integrates three core components: 1. an enhanced freeway mainline congestion management scheme considering the upstream flow modified from coordinated and sharing ALINEA, 2. dynamic ramp queue estimation and adaptive metering, and 3. coordinated signal control at adjacent intersections for regulating ramp inflows. Microscopic traffic simulation experiments, calibrated using real-world data from the Dawan Interchange in Tainan, Taiwan, were conducted to evaluate the system’s performance. Results show that R-CRAC consistently achieves higher freeway speeds and more stable ramp queue management than other strategies under the constraint of a short ramp length. Sensitivity analysis further identified optimal parameter settings that effectively balance operational performance across the freeway, ramp, and surface street subsystems. The findings demonstrate that R-CRAC offers a robust, practical solution for improving traffic efficiency at urban freeway interchanges.