Operational Impact of Shadow Evacuation on Regional Road Networks During Short-Notice Emergency Evacuations

Abstract

As part of evacuation planning, development of effective tactical and operational strategies are essential to safely and efficiently mobilize the public away from the threat. Evacuations are classified by the time between notification and the anticipated arrival of the threat which can be categorized as short, or no-notice emergencies. Emergencies involve the computation of the time required to evacuate the area of risk, which is the time to clear a radius of up to about 10-miles around the nuclear power plant, known as the emergency planning zone (EPZ). These evacuation time estimates (ETE) also account for the evacuation of the public outside the defined area of risk. Typically, this area extends five miles outside the EPZ boundary and it is commonly referred to as the shadow evacuation region. Although shadow evacuation could create significant traffic congestion that affects the EPZ clearance process, there is limited research quantifying this effect. The objective of this research was to study the impacts of shadow evacuation to the overall EPZ clearance process. To accomplish this, the research used microscopic traffic simulation to assess the effect of different shadow participation rates for three hypothetical nuclear power plants with distinct population sizes surrounding the plant (small, medium, and large) and roadway characteristics. The guidance in NUREG/CR-7002 for ETE studies recommends a 20 percent participation rate that was based on previous studies, research related to ETE demographics, public response, and other contributing factors. However, the 20 percent recommendation may be conservative. The results suggested that small population sites are not impacted significantly by varying the shadow participation rates. However, medium and large population sites showed a noticeable effect, particularly in those corridors with less capacity. If the shadow evacuation participation rate is increased to 40 percent, the ETE to evacuate 90 percent of the population is increased by up to 10 percent in medium-sized areas, and up to 19 percent in large areas. Under the same conditions, the ETE to evacuate 100 percent of the population increases by less than 5 percent for medium-sized areas and less than 3 percent for large areas.