Necessary condition for self-organized follow-me evacuation guidance using opportunistic networking

There is a serious problem in disaster evacuation guidance in urban areas: When a large-scale disaster strikes in the areas, how can many crowds of evacuees are smoothly evacuated to refuges without any major confusion by lack of disaster information? In recent years, we have proposed a method for disaster evacuation guidance using opportunistic networking where the evacuees gather and share disaster information using wireless communication by smartphones on the way in their evacuation, and we have shown numerically that our method drastically reduces evacuation time and efficient disaster information gathering. In our numerical simulations, however, there was an assumption that all evacuees totally follow our evacuation guidance. In this paper, we loosen the assumption for investigating the scenario that only a certain percentage of evacuees can follow our guidance, but the rest of unguided evacuees tends to follow movement of the majority of nearby evacuees. By this synchronous movement, a small group of evacuees including a core leader who instantly leads the other nearby evacuees by our guidance at the initial stage of evacuation will gradually aggregate nearby evacuees to form a self-organizing large group of evacuees, which creates a evacuation flow of evacuees along evacuation routes. We call these processes self-organized follow-me evacuation guidance. To evaluate the performance of the newly proposed guidance, we propose a model of Majority Voting Mobility (MVM) for simulating the formation of the self-organizing groups of evacuees. We use evacuation time and the cumulative number of evacuees arrived at a refuge for evaluation measures. Furthermore, we also consider a simple mean-field theory of MVM to discuss the necessary condition for the self-organized follow-me evacuation guidance. Consequently, we can numerically obtain reasonable numerical results which are consistent with an earlier study by Sugiman and Misumi, and we also show a threshold of the ratio of the core leaders to total evacuees that they can successfully form the self-organizing group.