Mitigating the impact of transportation network disruptions on evacuation

Homeland Security Presidential Directive-8 establishes a framework for national preparedness, including a vision, specific scenarios of concern, as well as a task list and target capabilities to be developed. The Department of Homeland Security Science and Technology Directorate has fostered enhanced resilience through sponsorship of tools to simulate the impact of the various disaster scenarios identified. However, the default simulations implemented for each of these scenarios implicitly assume availability of public transportation networks for task such as evacuation and response, yet such availability cannot be guaranteed without explicit consideration of the triggering events on transportation networks. Transportation is especially important as a majority of the scenarios indicate that over half of the affected population will need to be evacuated or self-evacuate and this population may be on the order of hundreds of thousands of people. Given the volume of traffic such scenarios may generate, the automobile transportation network will need to carry the majority of this flow of evacuees. Thus, methods to assess and mitigate the negative impact of transportation network disruptions on all aspects of disaster management, will be essential to reduce communal risk. This paper examines the criticality of public transportation in the context of the planning scenarios, suggesting methods to explicitly incorporate the impact of transportation network disruption. Methods based on dynamic traffic assignment are explored and applied to a small hypothetical scenario inspired by the 2010 Times Square car bombing attempt.