Research On Identification Of Critical Links And Robustness Optimization Of Urban Road Networks

Transportation is an important support for urban social and economic activities,and it has an important impact on residents' travel and logistics.Urban transportation is an open and complex system.During the operation of the system,it is often affected by emergencies such as natural disasters,extreme weather,traffic accidents,and malicious attacks.Some links play an important role in the urban road network.Once interrupted,they will significantly reduce the connectivity of the road network structure and affect the performance of the overall performance of the road network.The interruption of ciritical links will cause large-scale congestion of the road network,and even the entire road network will be paralyzed for a long time.How to accurately and efficiently identify critical links based on the dynamic complexity of the spatial and temporal distribution and evolution mechanism of the traffic flow in an urban road network,and to optimize the urban road network based on critical links to avoid or mitigate the negative impact of the interruption of critical links on the road network.This is a research with practical significance.This paper considers the operating characteristics of urban road networks when encountering unexpected events,and establishes an indicator for critical links identification and approaches that take into account the cascading failure effect to ensure the accuracy of the identification results.This indicator is a systematic indicator.It uses the full scan method to identify critical links,that is,each link in road networks is interrupted in turn,traffic assignment is performed,and the deduction in the efficiency of the road network caused by the link interruption is evaluated.In order to avoid the repeated iterative calculation of the full scan method and improve the calculation efficiency,a method for quickly identifying the critical links based on the traffic flow betweenness index is proposed.The rapid identification method based on the traffic flow betweenness index is based on the system index considering the cascading failure effect as a benchmark to calibrate the parameter in the traffic flow betweenness index,in order to achieve a balance of calculation efficiency and accuracy of the identification result.Finally,based on the identified critical links,road network partition optimization is performed to enhance the road network's ability to resist risks.The research in this paper mainly includes the following aspects:(1)Identification of critical links considering cascading failure effects in urban road networksAccording to domestic and foreign research on the identification of critical links in road networks,it is found that most of the critical links are identified using systemic indicators.Using systemic indicators,the variation in the operating efficiency of the road network system before and after the interruption of the link is determined to identify critical links.At present,the systematic indicators adopted basically do not consider the cascading failure effect of the urban road network.When encountering serious emergencies,the probability of the cascading failure effect of the crowded urban road network is high.This paper considers the characteristics of the urban road network when links are interrupted,and establishes a systematic index that takes into account the cascading failure effect.A dynamic multi-path traffic allocation strategy is constructed by combining the adaptability of the traffic network and considering the global information of the road network.The strategy not only considers travellers to re-plan the travel path based on the global network information under the condition of link interruption,but also considers the congestion dissipation of the interrupted link to characterize the evolution process of cascading failures in urban road networks more accurately.(2)Identification of critical links based on the traffic traffic flow betweenness index in urban road networksThe systemic index is to identify critical links using the full scan method.It is to measure the consequences of the interruption of each link from the perspective of the entire system.The urban road network has a huge number of links.If the full scan method is adopted,the calculation efficie ncy is poor,and even the operation cannot be performed.In order to improve the calculation efficiency,the traffic flow betweenness index is established by considering the link betweenness,link traffic flow and transferring demand.Based on this indicator,a method for quickly identifying the critical link in urban road networks is proposed.Based on the traffic flow betweenness index,the index value of all links is calculated,and candidate critical links are pre-selected.Finally,according to the values of the identification indexes of the critical links based on the cascading failure effect of all candidate critical links,the final critical links are determined.(3)Robust optimization of urban road network based on critical linksThe purpose of identifying critical links is to design or optimize road networks to reduce the impact of the interruption of critical links.If only the redundant capacity of critical links is increased,the traffic paradox may occur if the network is not optimized from the perspective of the network.That is,after the capacity of some critical links is improved,the overall efficiency of the road network is reduced.If the robust optimization design is performed for the entire large-scale urban road network,the computing burden will be heavy.Considering that the impact range of the interruption of critical links does not necessarily spread to the entire road network,it is often the consequence of the local road network within the area of its impact that is more serious.Based on this,the concept of robust optimization sub-region is proposed.Based on the interruption affected area,the idea of l-shell algorithm for community division in complex networks is used to generate the optimization sub-regions.Dividing the whole urban road network into many optimized communities will reduce the complexity of optimizing the whole road network.A robust optimization model is constructed with the goal of minimizing the systemic travel time of the road network before and after encountering the emergency,and the model is used to optimize the sub-regions to enhance the road network's survivability.(4)Empirical analysisTaking the road network within the scope of the ring road of Changchun as an example,the proposed method for critical links identification considering the effect of cascading failures,the method of quickly identifying the critical links based on the traffic flow index and the optimization method based on the critical links The effectiveness.The method for critical links identification based on cascading failure effect and the critical links identification method based on traffic flow index are used to determine the critical linkss of Changchun road network,and the calculation results and operation efficiency of the two identification methods are compared and analyzed.Based on the identified critical links,a robust optimization community is generated,and the constructed robust optimization model is used to propose a road network improvement plan.