Effect of phased evacuations in megaregion highway networks

Evacuation phasing or staging is a technique used to disperse traffic so that sudden, wide-ranging surges in travel demand do not overwhelm the available capacity of a road network during an emergency. Despite their many benefits, phased evacuations arc not an appropriate strategy for all locations and conditions. Even though researchers have evaluated various aspects of their use, little, if any, systematic study of staged evacuations has been conducted over large multiregional areas. A research effort to simulate staged evacuations in a megaregion addresses this information gap. Megaregions arc thought to be particularly vulnerable to evacuation problems because of their enormous populations, wide geographic expanses, and common locations along oceanic coasts or major inland waterways. A range of demand levels was used to investigate the effects of phased evacuation under different scenarios of road network congestion. Because mass evacuations arc infrequent and a full megaregion evacuation never has been conducted, this simulation-based framework offered an opportunity to create and assess a megaregion mass evacuation in microlevel detail. Simulation results revealed that the effectiveness of phased evacuations could vary widely according to the level of demand and congestion in the network. In general, no significant improvements could be gained by phasing when the network was only marginally congested or in the absence of congestion. The methods presented can be used for other locations and for other types of hazards, but whether similar llevels of effectiveness would be experienced in other locations or for other events is unknown.