An Operational Analysis of the Hampton Roads Hurricane Evacuation Traffic Control Plan

About the report:

The Hampton Roads region of Virginia has developed a hurricane evacuation plan to facilitate the movement of large numbers of vehicles as they attempt to leave the region in advance of a storm. Although the plan considers many aspects of hurricane evacuation, this evaluation focuses on its impacts on traffic operations. A traffic control plan (TCP) was developed that describes the procedures to be followed in the event an evacuation is ordered. Ramps providing access to I-64 are designated as open or closed, and many are metered in an attempt to influence the route choice of evacuees and thereby balance the demand across available evacuation routes. Although considerable work has gone into the development of the TCP, it has not been evaluated from a microscopic perspective to determine the performance characteristics with respect to traffic flow. This study provides that microscopic analysis for the freeway portions of the evacuation routes. The evaluation found that under less severe hurricane conditions (Category 1 or 2), the TCP performs reasonably well under the assumptions made in this study. The most significant assumption made was that all background traffic, including individuals evacuating their homes but remaining within the region, will not use the interstates during the evacuation period. Although background traffic will likely exist, there was insufficient information available in this phase of the study to assign background traffic to the network in any reasonably accurate manner. As the intensity of the hurricane intensifies to a Category 3 or 4, the TCP begins to be less effective. Ramp metering rates, designed in the TCP to ensure free-flowing conditions on the interstate mainlines, result in significant queues at the ramps and back onto the arterial network. Under Category 4 conditions, these queues would likely result in gridlock throughout the arterial network and lead evacuees to search out alternative routes, possibly negatively impacting the performance of those routes as well. The evaluation concludes that lane reversal is warranted under any storm predicted to make landfall as a Category 4 or higher and should be strongly considered for any Category 3. The study further finds that when lane reversal is implemented, the ramp metering rates should be significantly increased to reduce ramp queuing and allow more efficient use of available mainline capacity. The recommendations offered in this report will help to ensure an efficient evacuation of vehicles from the Hampton Roads region, should one be required. The revised ramp metering strategies and guidance on the use of lane reversal will help to maximize the available capacity provided by the interstate routes. Assumptions made throughout the study could render the results uncertain. Background traffic using the interstate routes could add to the congestion reported here. In addition, conditions outside the bounds of the network modeled in this project could negatively impact evacuating vehicles leaving Hampton Roads.

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