Pedestrian–bus route and pickup location planning for emergency evacuation

Lu, Weike; Wang, Feng; Liu, Lan; Hu, Guojing; Mao, Jiannan · 2021 · DOAJ

DOI: 10.3846/transport.2020.13674

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Summary

This paper addresses the challenge of planning efficient bus-based regional evacuations for urban environments prone to emergencies such as hurricanes or floods, particularly for transit-dependent populations. The authors develop an optimization-based decision-support model that integrates pedestrian evacuation guidance with bus route planning. The primary research objective is to minimize the total evacuation duration time—defined as the time until the last evacuee reaches a shelter—by simultaneously determining optimal pickup nodes for pedestrian assembly and allocating a constrained bus fleet to transport evacuees to designated shelters. This approach distinguishes itself from prior studies by explicitly accounting for bus quantity and capacity constraints, whereas previous models often assumed unlimited vehicle availability. The methodology employs a mixed-integer nonlinear programming (MINLP) model that couples a pedestrian network with a bus network. Evacuees travel on foot from origin nodes to selected pickup nodes, where they board buses for transport to shelters. The model incorporates several key constraints: flow balance for pedestrian routes, a "one-one-one" evacuation structure (one origin to one pickup node to one shelter), and bus resource limitations requiring multiple trips if demand exceeds capacity. The objective function minimizes the upper bound of evacuation times across all origins. The model was implemented using the General Algebraic Modelling System (GAMS) and tested on a modified Sioux Falls street network from North Dakota. Two scenarios were evaluated: Scenario 1 utilized 21 buses with sufficient capacity for single-trip transport, while Scenario 2 reduced the fleet to 14 buses, necessitating multi-trip optimization and balanced bus assignment across multiple pickup locations. The results demonstrate the model’s effectiveness in optimizing evacuation logistics. In Scenario 1, the optimal solution assigned all 21 buses to a single pickup node (node 15) to transport evacuees to shelter node 22, achieving a minimum evacuation duration of 20 time units. This configuration was driven by the shortest bus route and the ability to transport the total demand of 630 evacuees in a single trip. Validation via 1,000 random evacuation schemes confirmed that no random allocation yielded a duration shorter than 20 time units, verifying the optimality of the GAMS solution. In Scenario 2, with fewer buses, the model successfully distributed buses across multiple pickup nodes and shelters, optimizing routes to handle the increased number of required trips. The study confirms that the model can simultaneously determine pickup locations, pedestrian routes, and bus assignments under resource constraints. The significance of this work lies in its practical application for emergency management in densely populated areas. By integrating pedestrian and bus networks and accounting for realistic fleet limitations, the model provides a robust tool for minimizing evacuation times. The findings highlight that consolidating evacuees at strategically located pickup nodes can significantly reduce duration when bus capacity allows, while distributed pickup strategies are necessary when resources are scarce. This approach offers a more comprehensive planning framework than previous models that ignored bus constraints or treated pedestrian and vehicular movements separately.

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• evacuation egress