On the Use of Congestion Information for Rerouting in the Disaster Evacuation Guidance Using Opportunistic Communication

In recent years studies on disaster evacuation guidance effective against situations of large-scale urban disasters have been undertaken. Recently we have proposed the disaster evacuation guidance using opportunistic communication where evacuees collect disaster information of the locations of impassable and congested roads in their smartphones by themselves and share it with each other opportunistically by short-range wireless communication between nearby smartphones in order to not only navigate crowds of evacuees to refuges, but also rapidly aggregate the disaster information in real time. The proposed guidance was valid in evacuation scenarios under the condition that the mobile communication is disabled by disaster. We numerically showed by simulating a simple mathematical model that the guidance effectively shortened evacuation time of the evacuees. Since the crowds of evacuees simultaneously rush to refuge areas in the evacuation, on the other hand, the emergence of congestion by evacuees is inevitable and the evacuation time could be seriously delayed by the congestion. In this paper we investigate effects of the use of congestion information on the evacuation time by switching a detour evacuation route around congested roads. We introduce three simple algorithms to divert the route and numerically compare their performances using a new stochastic congestion model. In consequence we find that the use of congestion information has less impact on the evacuation time than that of the information of impassable roads, and also that slower route switching decision coming around congested roads is worse in the performance because evacuees tend to be sandwiched between some congested areas and are forced to go back and forth in vain by repeated evacuation route changes.