Modeling and Analysis of Evacuation Contraflow Termini

Over the last five years, the Department's of Transportation in 12 coastal states threatened by hurricanes have developed plans for the implementation of contraflow traffic operations on freeways during evacuations. Contraflow involves the use of one or more inbound travel lanes for the movement of traffic in the outbound direction. It is both a logical and cost effective strategy because evacuation traffic can be loaded into underutilized inbound lanes, thereby significantly increasing outbound capacity without the need to construct additional lanes. This paper summarizes the results of two recent studies to evaluate the implications of contraflow evacuations on freeways. The research focused on what are widely regarded to be the most critical locations of contraflow segments, the initiation and termination points. The termini configurations are important because they effectively dictate the capacity of these segments because they control how many vehicles can get in and out. In the research, traffic simulation models were developed to simulate the operation of planned configurations under varying levels of traffic demand to assess their operating characteristics. The results showed that many of the current designs of the initiation and termination points will likely restrict the ability of these segments to be used to their maximum effectiveness. Another key finding was the extent to which the spatial and/or temporal spreading of traffic demand can yield significant benefits to the overall effectiveness of contraflow freeway evacuations. It is hoped that with an increased awareness of these issues, these findings can be used to enhance the effectiveness of existing evacuation plans.