Incident Occurrence Modeling during Hurricane Evacuation Events: The Case of Alabama's I-65 Corridor

Contraflow on major evacuation routes is one scheme that has been adopted in many Gulf and eastern coastal states for hurricane evacuation. The idea is to reverse one direction of the roadway in order to accommodate the often substantially increased travel demand moving away from the impact area. Efficient planning and operation is critical to a successful contraflow implementation. Alabama has an approximately 140-mile contraflow segment on I-65 between exit 31 and exit 167 and has carried out contraflow operations several times in past hurricane evacuations. The timing for the deployment of equipment and personnel and the initiation and termination of actual contraflow affects the effectiveness, safety, and cost of the operation. Researchers from the University of Alabama were tasked with the design of a decision support system for contraflow evacuation planning. The conceived decision support system consists of three main modules: the demand module, the network optimization module, and the incident and characterization module. This paper focuses on the design of the traffic incident generation and characterization module of the planned decision support system. 1. Introduction Massive evacuations due to tropical storms, hurricanes, and other extreme weather events are becoming routine events in coastal regions around the globe. The normal response to these occurrences is to evacuate inland from the coast. Normal traffic flows turn into congestion, frustration, and gridlock. This reduces the number of vehicles that can leave the affected area if an evacuation order is given. The potential risk for catastrophic loss increases if the hurricane strikes stalled traffic and necessitates further evacuation planning. Among the most common evacuation strategies flowed by traffic management officials during such events is “reverse-laning” or “contraflow.” Contraflow is the process of reversing one direction of traffic on specific routes to facilitate overall evacuation flow. This procedure is generally applicable to interstates, referred to as “denied access routes,” since traffic control can be applied to interchanges and terminal areas. During contraflow operations an increase of vehicular traffic incidents should be expected. Traffic incidents are defined as nonrecurring events, including accidents, that lead to the overcongestion or saturation of a network of roads. During large-scale evacuations such as in the case of a hurricane evacuation, traffic incidents significantly extend the travel time of evacuees; thus, the time needed to completely empty the