Traffic Signal Timing for Urban Evacuation

Chen, Ming; Chen, Lichun; Miller-Hooks, Elise · 2007 · OpenAlex-citations

DOI: 10.1061/(asce)0733-9488(2007)133:1(30)

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Summary

This thesis addresses the critical gap in urban evacuation planning regarding traffic signal timing. While significant research has focused on freeway management and routing for evacuations, there has been no systematic consideration of how signal control impacts traffic flow during no-notice urban evacuations, such as those triggered by terrorist attacks or hazardous material releases. The study aims to determine the state-of-the-art in signal timing for evacuation and to assess the effectiveness of various timing plans in facilitating the rapid movement of evacuees from endangered urban areas. To achieve this, the author developed a traffic simulation model using data from Washington, D.C., specifically focusing on two primary evacuation routes. The experimental design involved creating two master scenarios—a terrorist attack near the Capitol and a federal shutdown—each containing multiple sub-scenarios to account for variables like traffic incidents, contraflow operations, and roadside parking. Evacuation demand was estimated using census data, with simulations run under average and worst-case demand conditions. The study compared existing signal timing plans, including standard PM-peak plans, a 240-second cycle plan, and flash mode, against alternative plans designed specifically for evacuation. Performance was measured by the total number of vehicles evacuated over a 10-hour period and the average vehicle delay. The results indicate that significant trade-offs exist in setting signal timing for evacuation. Long cycle lengths were found to reduce overall evacuation times by prioritizing main evacuation routes, but this came at the expense of increased delay on minor roadways. The study found that the most effective compromise plans employed cycle lengths greater than those used in ordinary peak hour plans. These optimized plans allocated significantly more green time to main evacuation routes compared to minor roadways, thereby increasing the capacity of the primary network for evacuees. The simulation demonstrated that resetting signal timing to favor evacuation flows could substantially improve network clearance compared to standard operational plans or flash modes. The significance of this work lies in its provision of empirical evidence for traffic engineers and emergency planners. It establishes that signal timing is a potent tool for managing urban evacuations, particularly in no-notice scenarios where traffic demand arises suddenly and intensely. By identifying that longer cycles with biased green time allocation improve evacuation throughput, the thesis offers specific, actionable recommendations for developing evacuation signal timing plans. This contributes to the broader field of emergency transportation operations by shifting focus from solely freeway management to comprehensive urban network control, potentially reducing fatalities and injuries by minimizing the time required to move populations to safety.

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• evacuation egress