| Road network is the most basic component of urban infrastructure and plays a vital role in economic development.In developing countries,due to the rapid urbanization,urban road construction projects often lack forward planning,and ignore the impact of extreme weather disasters such as rainstorms and waterlogging.Under the rainstorm scenario,insufficient drainage capacity leads to severe waterlogging on roads,and the failure of key roads will affect the performance of the whole network which will greatly influence commute efficiency and experience,and evenly threaten the safety of the city.From the perspective of urban sustainable development and urban safety guarantee,how to identify and improve the vulnerability of the traffic network under the rainstorm scenario,so as to prevent and reduce the impact caused by extreme disasters has become a hot research issue.In order to assess the vulnerability of urban road network in a more comprehensive way and explore the improvement strategy,this study takes the central urban area of Wuhan city as the research scope to carry out the research of road vulnerability.First,the urban waterlogging maps were obtained under three scenarios:10-year,30-year and50-year return period,based on the hydrodynamic model.According to the maps,the risk analysis of waterlogging was carried out to identify the failure roads under the rainstorm scenario.Secondly,based on Baidu commuting OD data and route analysis tool in Arc MAP10.5,the commuting route and travel time of residents under multiple scenarios were obtained,and the commute loss of residents caused by each failure roads were calculated to represent the vulnerability.And high-risk sections were identified according to the vulnerability results.Finally,based on the bivariate Moran′s I model,the correlative factors and mechanism leading to the vulnerability of the road were explored,which provided classification basis for spatial planning and management,and targeted strategies for improving the vulnerability of the road network were proposed.The key conclusions of this study are as follows:(1)Three rainstorm scenarios,10-year,30-year and 50-year,were selected to simulate rainstorm waterlogging in central Wuhan,and risk analysis was conducted according to the simulation results.The waterlogging areas are mainly distributed in Jianghan District and Jiangan District in the northwest of central Wuhan.With the increase of rainfall intensity,the waterlogging area is expanding and the inundation depth is increasing,and the impact of roads and commuters are also increasing.Under the three scenarios,the inundation area expanded from 62.93km~2 to 90.24km~2 and101.43km~2,and the inundation road length increased from 72.18km to 150.45km and182.45km.The percentage of commutes inundated increased from about 3%to 7%and10%.(2)Based on commuting data and route analysis tool,this study simulated residents’commuting trips under multiple scenarios,and analyzed the impact of residents’commute caused by waterlogging.It was found that the proportion of completed trips decreased from 83.62%in the 10-year scenario to 63.03%in the 30-year scenario and 33.43%in the 50-year scenario.The maximum commuting time increased from 44.76 minutes in normal scenario to 81.33 minutes,106.35 minutes and136.06 minutes in rainstorm scenarios.The maximum travel distance increased from19.54km to 25.11km,32.85km and 39.32km.In terms of vehicle flow distribution,with the increase of rainstorm intensity,flow distribution is increasingly uneven.In terms of regional commuting characteristics,in 10-year scenario,the residents’commutes are mainly diverted,in 30-year scenario,the proportion of unpassable residents increases,and in 50-year scenario,unpassable resident becomes the dominant state in the central city.In terms of commuting time,the proportion of residents’medium-time commute and long-time commute in the rainstorm scenario is increasing continuously,and the proportion of long-time commute in the peripheral streets of the central city is growing the fastest.The short-time commute and medium-time commute are dominant within the second Ring road.(3)Based on the commuting loss perspective,the vulnerability assessment index was designed to evaluate the road vulnerability under the rainstorm scenario.The results showed that the spatial distribution of road vulnerability in central Wuhan had three characteristics:the wider the inundation area,the higher the road vulnerability;Expressway and main roads with heavy commuting flow have higher vulnerability.Roads along the river and around the lake have higher vulnerability,while the densely distributed secondary roads is lower.Only about 1%of roads in the central urban area showed high vulnerability under the 10-year scenario,namely Zhuodaoquan South Road,Fengsheng Road,Xiongchu Avenue,Chukang Road,Hanxi Third Road,Huquan Street.Under the 30-year scenario,the high-vulnerability sections clustered in the area around Nanhu Lake,the central area of Hankou and the middle section of both sides of the Han River.In the 50-year scenario,roads with high vulnerability are mainly displayed in Huquan Street,Xiongchu Avenue,Nanhu Avenue,Luoxin Road,Xiongzhuang Road and other areas.Otherwise,50-year rainstorm scenario is a critical scenario for Wuhan.In this scenario,regional evacuation or rescue of residents is more important and urgent than traffic control and facilitation.(4)Based on the bivariate Moran’s I model,the correlative factors of road vulnerability were explored.It was found that there was a significant spatial positive correlation between road vulnerability and inundation area,and the significant correlation regions were mainly distributed in the northwest of the central urban area.There is a significant positive correlation between road vulnerability and commute traffic flow,and the significant correlation regions were concentrated in Hankou central district,Wuchang central district and the periphery of the study area.The correlation between road vulnerability and road coverage density is weak in global space,but significant correlation exists in local space.(5)Based on the two perspectives of zonal optimization and global guidance,the following strategies are proposed to improve road vulnerability in central Wuhan.In the aspect of zonal optimization,drainage facilities should be improved and urban sponge area should be created for waterlogging prevention zone.Three-dimensional traffic system should be built and the traffic guidance during the disaster should be strengthened for traffic diversion zone.Key road network structure should be improved and the supply of traffic facilities should be increased for road constructed zone.In terms of the global guidance,we should improve the point-polyline-polygon control and guarantee system,and strengthen the pre-incident and post-incident road management.Then we should create a multi-center urban spatial layout and improve the allocation of living neighborhood service functions.Lastly,we should also construct intelligent traffic management system to realize efficient and scientific traffic supervision.In this study a research framework of road vulnerability assessment is constructed,and the research of vulnerability assessment and improvement of urban road network under the rainstorm scenario is carried out based on the commuting loss perspective.This study solves the problems of single perspective,data distortion and small scale in the current vulnerability research.The results of road network vulnerability assessment can help to understand the distribution of vulnerable road network,provide direct support for the priority of traffic system control and resource allocation within the central urban area of Wuhan city,and provide theoretical support and decision-making basis for waterlogging risk control and urban planning. |
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