Optimal critical infrastructure retrofitting model for evacuation planning

In emergency situations, it is necessary to safely evacuate the population in order to save lives. The road network infrastructure is vulnerable for extreme events, and as a result its ability to supply the required capacity can be seriously hampered. Hence, it is crucial to identify those critical segments which prohibit safe evacuation, and find an optimal retrofit scheme at the network level in order to minimize evacuation time. This work introduces an emergency evacuation model that considers infrastructures vulnerability, event location and magnitude, road network, transportation demand and evacuation areas in order to identify the critical infrastructures and recommend budget allocation for increasing network capacity for minimizing evacuation time, given budget alternatives. The infrastructures' analysis was based on the knowledge about mechanics characteristics of a set of bridges, and about a set of possible seismic scenarios related to the area of interest. By using fragility curves of bridges, the damage state of them has been assessed. By making a series of hypotheses on how a bridge damage state can influence links' functionality, reduced capacity was assigned to the road network. The result is the estimation of the retrofit cost needed for a specific seismic scenario, considering the most effective retrofit intervention type, previously identified for each bridge. The infrastructures' analysis results were used by the evacuation model for optimal budget allocation of retrofits strategies in order to attain a desired evacuation time frame. The procedure has been applied to an urban network in north Italy.