Mobility Benefits of Intermediate Crossovers on Contraflow Facilities during Hurricane Evacuation

A contraflow facility, in which the direction of traffic on one or more travel lanes is reversed to increase outbound capacity, is a major component of hurricane evacuation plans in many coastal states. Contraflow facilities typically are implemented when significant evacuation demand is expected (e.g., during a severe hurricane). Typical contraflow plans have one upstream crossover that routes vehicles into the contraflow lanes and one downstream crossover that routes vehicles back into the regular lanes. How can contraflow facilities best be used to optimize evacuation performance? The impact on mobility of additional intermediate crossovers between the beginning and termination points of contraflow is investigated. The proposed heuristic algorithm is the first attempt in the literature to provide a systematic approach–-with iterative elimination–-to determine the critical intermediate crossover locations that provide maximum improvement in evacuation performance. Results of a case study of I-64 in Hampton Roads, Virginia, indicate that adding intermediate crossovers improves network performance for medium-and high-demand evacuation situations. For low-demand situations, the addition of intermediate crossovers does not improve network performance. Therefore, any consideration of intermediate crossovers for low-demand evacuations must be solely to provide access to roadside facilities such as gas, food, and emergency services. For medium- and high-demand situations, the average travel time improved 28% when four intermediate crossovers of the 44 potential crossover locations were deployed in the I-64 corridor.