Influence of departure time spans and corresponding network performance on evacuation time

Estimation of the time needed to evacuate a population from a threatened area in case of a disaster is one of the main issues in the design of an evacuation plan. The challenge is to develop a strategy that optimally uses the network capacity to minimize the total evacuation time. In this paper, the impacts of various departure time spans on evacuation time and network performance are investigated with a microscopic traffic simulation model. The network performance has been analyzed with the use of the macroscopic fundamental diagram (MFD). Although the MFD usually shows a decrease in travel production after a peak is reached, this is not the case in the simulation of evacuation scenarios. The outflow of the network remains constant because it depends on the capacity of local bottlenecks upstream of the limited number of destinations, but the number of vehicles in the network increases because of an increase in congestion. Although the overall network performance is insensitive to the evacuation time spans, it is observed that for shorter evacuation time spans, internal gridlock effects cause lengthy delays for specific groups of drivers, who, it turns out, are unable to leave the network in time. The use of a simulation study in combination with an MFD can therefore identify the routes used and the bottlenecks on these routes leading to the destinations, while the maximum production level (defined as the number of arrivals, determined in the MFD) indicates the optimal level of demand.