Impact of Dynamic Ramp Closures on Urban Expressway Traffic: A Field Study

Ramp controls, such as ramp metering and closure, have been known as a promising strategy for alleviating traffic congestion in urban expressway networks. While ramp metering is a widely adopted practice globally, dynamic ramp closure has received less attention. The key distinction between the two lies in their signaling and effects on queue formation: ramp metering utilizes short-cycled signals to manage entering traffic, potentially causing long queues during peak arrival times, whereas dynamic ramp closure conveys a noncycled no-entry signal, prompting drivers to plan alternative routes in advance, thereby effectively preventing queues. This difference suggests that dynamic ramp closure has potential to avoid the gridlock issues at adjacent intersections due to spilled queues. In this study, we have developed and implemented the world’s first city-wide dynamic ramp closure system on urban expressways in Changchun, China, leveraging data from both fixed-point detectors and connected and automated vehicles (CAVs). Our field analysis revealed that dynamic ramp closure yields significant improvements, with expressway traffic speed increasing by over 20% and throughput by 10% compared to scenarios without control. Additionally, our research indicated that travel speeds on parallel ground streets remain relatively unaffected, suggesting an overall improvement over the entire road network. We also examined driver noncompliance with dynamic ramp closures and outlined how traffic departments educated the public and mitigated noncompliance. The successful implementation of this dynamic ramp closure system serves as a compelling demonstration of its effectiveness, providing valuable insights and potential solutions for other cities grappling with similar traffic congestion issues.