Urban Road Network Vulnerability Assessment Model Research

Road network is the vessel of a city.However,with the development of economy,the number of vehicles increases gradually,which directly makes the contradiction between traffic supply and demand more and more acute.Traffic jam almost occurs every day.In addition,some emergencies like natural disasters and traffic accidents make the traffic circulation more difficult.News that emergencies like heavy rain,road landslide and traffic accidents lead to severe traffic jam are not uncommon.It is possible for us to do targeted prevention,and adopt traffic dispersion measures to avoid the expansion of jam when failure occurs if we could make a research on the vulnerability of urban road network and find its weak points.Then impacts of emergencies on road network as well as economic loss will be reduced.Urban road network is the object of research.Through searching relevant literatures and analyzing the existed estimate methods,the research category of road network vulnerability was found out.Based on the influencing factors of vulnerability,generalized cost variation M1,network efficiency index M2,network robustness index M3,etc.,total seven indices were applied to evaluate the road network vulnerability respectively considering the accessibility and the relation of supply and demand.After that,the results of comprehensive evaluation were achieved by CUBE software and simulation software DTALite.Lastly,the practical application value of the evaluation of road network vulnerability was analyzed from disaster prevention and mitigation.The following are the main works:(1)The principle theoryFirstly,the similarities and differences between the existed definitions of vulnerability were analyzed from two aspects of narrow sense and broad sense.And under the condition that part of roads are not available,the reduction of performance of road network system was the focus of the study.Secondly,the conceptions of riskiness,reliability,etc.,six indices which are analogous to vulnerability,were illustrated and analyzed.Lastly,the existing studies were reviewed from the view of beyond macroscopic,macroscopic,medium and micro.(2)The influence factors,evaluation methods and indicesFirst,the factors influencing the road network vulnerability and correlativity were expounded respectively from the aspects of internal and external.After that,the evaluation methods of road network performance were classified according to the disaster life cycle,the index type,the uncertainty modeling technology,the analytic method and the optimization method.Next,the evaluation indices of vulnerability were divided into four types,respectively based on accessibility,based on the relation between supply and demand in static model or dynamic model,and the others.And the typical calculation formulas were listed.(3)The comprehensive evaluationSeven indices on the basic of accessibility and the relation between supply and demand were selected,including generalized cost variation M1,network efficiency index M2,network robustness index M3,etc..M1 ~ M5 neglect the effect of dynamic characters and reverse propagation of congestion,they would be achieved by CUBE software.However,M6 ~ M7 consider the above effects,and they were applied into the case study,which was conducted by DTALite.(4)The analysis of practical valueFrom the view of disaster prevention and reduction,the evaluation of vulnerability before accidents could be used as the consequence evaluation indices,and help to recognize the weak point in network,and provide reference for emergency resources distribution.And in disaster relief,the practicability and function of vulnerability in three stages,including the assessment of current situation,making strategy and determining the priority of recover.Besides,the practical value in other aspects was introduced briefly.