Evaluation of traffic mitigation strategies for pre-hurricane emergency evacuations

Hurricanes cause tremendous and expensive threats to both public and private property. More urgently, affected residents face life threatening conditions. Therefore, it is imperative for government officials and citizens to have an efficient plan when an evacuation is ordered. Leading up to Hurricane Irma in September of 2017, significant traffic congestion occurred during the ordered evacuation. Mitigation strategies that were implemented could not handle the high volume and demand of vehicles. In addition, resources needed to support mass vehicle evacuations, fuel and water, become scarce due to the high demand and can prevent high risk evacuees from getting to safety. It is critical to perform a scenario analysis to analyze and compare strategies that mitigate vehicular traffic congestion during an emergency evacuation. This study investigates how a variety of strategies could affect traffic flow during an evacuation when the highway infrastructure exceeds capacity with vehicles all traveling in the same direction. A baseline simulation model was constructed in VISSIM, a traffic microsimulation software, and separate simulations were run with adjustments to the baseline structure to reflect implementations of different mitigation strategies. Results from each strategy's simulation are compared to the baseline to evaluate the impacts of the strategy on the number of people and vehicles that make it to safety. Measured in discharge rates, the contraflow strategy showed the most improvement over baseline conditions, and an exponential relation between discharge rate increases and demand scaling was also found to be accurate.