关键词: 应急疏散, 路径规划, 算法优化, 洪灾避难, MiniGIS

Abstract:

Well-planned evacuation routes definitely contribute to reducing traffic congestions and mitigating logistics costs during an emergency evacuation. With an objective to minimize the total evacuation time, an approach to seek optimum evacuation routes in a capacity constrained road network was presented in this paper, and then it is carried out based on a scenario with severe surge floods affecting an island county in Zhejiang province, China. The classical Dijkstra algorithm is improved by addressing the issues aroused with respect to evacuees' demands, traffic congestion, and the equal accessibility to and assignment of relief resources. Besides, regarding the fact that, since the evacuee units contain a large population, it is hard to find a closest shelter with enough capacity at one time, thus the mixed split delivery model is adopted. Namely, a unit might be divided into several groups and sent to different shelters separately. Using C#, an applet with built-in algorithms named MiniGIS is developed for the visualization of the dynamic evacuation flow. As presented in this paper, the ideal algorithm, though being capable of finding out the optimal evacuation routes, is based on a highly ordered scenario in which only simple traffic congestion is considered. Next, the additional delay caused by mode transferring and slow down at road cross-sections, turnings and crowded segments is taken into consideration. In addition, the delay-improved algorithm, which records the state of each group at road conjunctions, is able to calculate the total delay if given the time when evacuation state swifts from one to another. Undoubtedly, it provides more reliable results than the ideal algorithm does; however, due to route adjustments, several retrogressions are captured in the routes planned by delay-improved algorithm using the tracking animation in MiniGIS, implying that a certain vehicle is required to return to a former earlier location before heading toward the destination according to the new planned route. Considering routes with retrogressions are not common and easily being identified and adjusted, such routes are artificially fixed and then input to the retrogression-improved algorithm, which would calculate the new evacuation time and meanwhile avoid redundant retrograde motions. Basically, though the total travel time would slightly exceed that of delay-improved algorithm, results of retrogression-improved algorithm is still regarded as the optimum solution giving priority to efficient evacuation management and resource economization.

Key words: emergency evacuation, routes planning, algorithm optimization, flood events, MiniGIS