Research On Urban Roadway System Resilience And Safety Evaluation Under The Influence Of Flood Disaster

With the development of China’s economy and the improvement of infrastructure,urban critical infrastructure system has become more complex and interactive,which make it more vulnerable to damage impact and difficult to restore its capability.Urban roadway system is one of the core infrastructures to ensure the stability of social and economic developments.It is more susceptible to flood disasters and consequently lead to huge economic losses.Flood disasters can directly destroy the roadway infrastructure,impact the pedestrians and vehicles,damage the roadway network,interrupt the vehicular mobility and cargo transport,which can make it difficult for the plagued city to maintains its basic functionality.Considering that the unpredictable and destructive nature of disasters can bring about serious safety issues to the urban transportation system,safety researchers pay great attention to the damage as a result of disaster events and would like to understand how a system recovers back to a stable state.The focus of traffic safety studies have gradually shifted from the traditional system risk to resilience and sustainability.The thesis attempts to study the influence of flood disasters on the transportation network and evaluate the resilience and safety aspects of the urban roadway system.The study adopts roadway segment saturation rate to describe the changes of system performance upon damage in the process of quantifying the resilience and safety of urban road traffic system.The study builds capacity recovery model which includes several core concepts of resilience characteristics(i.e.,absorptive capacity a,recovery rate b,and recovery level λ).The parameters a,b and λ can describe the performance changes under various hazardous scenarios,and thus show the flexibility for the application of the model.The study integrates the topology property of road network with recovery speed(as one of the system resilience parameters)and treat the evaluation of roadway topology structure as the segment and node importance,which paves the way for the emergency rescue under the flood impact.Furthermore,in order to evaluate the system resilience of the roadway network,the study utilizes crash rate and severity under different speed intervals in combination with safety performance function(SPF)during the change of system performance.The thesis uses the CRITIC method to establish a comprehensive evaluation model which can account for safety and resilience concurrently to capture how system safety changes with resilience.Finally,the research employs the roadway system in Ninghai County as the case study to implement the proposed methodology and put forward with the recommendations for the emergency rescue response.The study unearths some interesting relationships between vehicle speed and crash rate/severity.Crash rate of urban roadways decreases with the increase of vehicle speed,while the proportion of fatal crashes is increased.The results show that freeways are relatively safer as opposed to other urban roadways.In terms of system safety and resilience evaluation,the thesis finds that the system safety will decrease along with the system performance levels upon the flood impacts.More importantly,the system safety shows a hysteresis effect corresponding to the decline of the system performance,that is,when the system performance level reaches the lowest point,the safety level still keeps declining.During the system recovery phase,the most dangerous circumstance of the system does not occur in the place where the roadway damage is the most serious but the roadway segment where traffic detours take place.In summary,the following suggestions are recommended for government management and individual drivers.First,when urban roadways suffer from flood events,the government should broadcast the information in time about road water-logging to avoid serious safety crashes.Second,during the emergency rescue period,government officials should strengthen the management of damaged but not completely blocked road segments to avoid the increase of safety crashes caused by vehicle detours.Third,drivers should minimize the necessity of travel during floods and choose the arterials with less water accumulation while avoiding secondary and local roads for detours if they have to move.