Evaluation And Optimal Allocation Of The Accessibility Of EMS Under The Pluvial Flood And Traffic Congestion Scenarios

Emergency medical service(EMS)is an independent branch of a city’s medical resources.Being extremely time-sensitive,EMS is vulnerable to adverse weather conditions and traffic congestion.In the context of global warming and rapid urbanization,pluvial flash flood has been quite often in urban areas,causing phenomenon like “bound to flood whenever it rains” and “vehicles can hardly move at peak hours”.Once roads are cut off due to pluvial flood or traffic congestion,the ambulances will be forced to detour,slow down or even stop.Thus,the response time of EMS will be extended,which might bungle the chance of saving patients.In recent years,how to scientifically evaluate the accessibility of EMS,ensure the timely response of EMS,and realize the equity of EMS has gradually become a thorny concern of experts and relevant government departments.For the case study,we selected the inner-city of Shanghai as the study area.By constructing the “pluvial flood—traffic congestion” scenarios,we analyzed the effect of pluvial flood,traffic congestion and both of them on the EMS.And then,we employed the Two-step Floating Catchment Area method(2SFCA)to calculate the accessibility of EMS under different scenarios.Based on the results of accessibility analyses,we used the Lorenz curve method and Gini coefficient to evaluate the equity of EMS resource in the study area.Finally,we provided relevant strategies for optimizing the EMS system to improve its efficiency.The main conclusions are as follows:(1)On constructing compound scenarios by incorporating pluvial flood and various traffic conditions: In order to model pluvial flood scenarios,the precipitation of 100-year return period was calculated based on the Shanghai rainstorm intensity formula and Keifer and Chu method.Then,FloodMap-HydroInundation 2D,a hydrodynamic modeling toolset,was used to simulate the pluvial flood under the 100-year precipitation scenario.Meanwhile,based on tile map method,Baidu Map was used to reveal the real time traffic status during the morning rush hours,the leisure hours and the evening rush hours.Then,the road situation information under three periods was obtained through splicing,integration and vectoring.Finally,a total of 8 compound scenarios were generated by incorporating 2 weather conditions and 4 traffic congestion levels.(2)On studying the effect of pluvial flood and traffic congestion on the accessibility of EMS: The shortest travel time between the EMS stations and the census tracts were calculated.Then we analyzed the service areas of EMS under different scenarios based on the accessibility range analysis method.Meanwhile,2SFCA method was used to calculate the spatial accessibility of EMS in the study area under different scenarios.The results show that the accessibility of EMS is mainly attenuated along the road network with the emergency station as the center.It was clear that pluvial flooding and traffic congestion may affect EMS.First,ignoring traffic congestion to evaluate the accessibility of EMS will seriously overestimate the accessibility of EMS.Second,the spatial and temporal distribution of traffic congestion will affect the evaluation results of accessibility,among which the accessibility during evening peak hours is the worst.Third,areas with sparse roads and simple road networks are less affected by the spatial and temporal changes of traffic congestion.Fourth,the pluvial flood will reduce the accessibility in some census tracts,evenly where there are areas of high accessibility.Fifth,the EMS has the smallest service scope and the lowest efficiency under the “pluvial flood-evening rush hour” scenario.(3)On assessing the equity of EMS under different scenarios.According to the distribution of accessibility of EMS under different scenarios,Lorentz curve and Gini coefficient were adopted to evaluate the equity of EMS in the study area.The results show that the equity of EMS under the fine weather condition or pluvial flood scenarios is excellent,given that all ambulances can move at the maximum speed.However,when considering the traffic congestion,the equity of EMS declines sharply in all kinds of weather scenarios,and is in the absolutely unfair level.In addition,compared with the fine weather condition,pluvial flood may reduce the equity level,which increases Gini coefficient by approximately 0.02.Overall,it is clear that the equity level under the fine weather condition is better than that under the pluvial flood scenarios,and the equity level during leisure hours is better than that during the morning peak hours and then the evening peak hours.(4)On studying the optimization strategies for EMS under different scenarios: According to the distribution of EMS in the inner-city of Shanghai,the maximum coverage model method was adopted to optimize the layout of EMS under “pluvial flood-evening peak hour” scenarios.Then,from the perspective of constructing traffic network,the ability of urban flood control and civic awareness,scientific suggestions were provided to improve the efficiency of EMS.