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Modeling and Performance Assessment of Contraflow Evacuation Termination Points

About 20 hurricane evacuation contraflow segments are planned for use in the United States. When activated, these routes will serve as lifelines for people fleeing the potential destruction of approaching storms. The termination points of these segments are critical because they move traffic from the reverse-flowing lane into the normal flow direction. They are also thought to affect the overall effectiveness of the sections significantly because they can regulate the amount of volume that exits the section. The research effort described in this paper was undertaken to assess and compare the operational characteristics of contraflow evacuation termination point designs that would be used under threat from catastrophic storms. Among the developments of the research was an approach and set of assumptions for using CORSIM to model contraflowing freeway traffic under evacuation conditions. These models were used to assess and rank the planned termination designs comparatively and to identify the factors that made some designs more effective than others, including the effect of reducing traffic volumes before the termination. The quantification of the operations revealed several important concepts relative to the use of contraflow evacuation segments. First, it is advantageous to maintain all lanes through the termination point with split rather than merge designs. Also, it is advantageous to reduce the volume entering the termination point by maintaining exit points along the route. The study suggests that merge zones located after exits, instead of before them, and the use of channelization or separation devices well in advance of forced maneuvers can enhance the quality of the flow through the termination vicinity.