Cascading Failure Evacuation Path Planning Of Urban Road Traffic Network Based On Comprehensive Importance Of Nodes

With the continuous growth of traffic demand,the traffic pressure of urban road network is increasing,and the traffic congestion problem is becoming more and more serious.In the urban road network,the occurrence of congestion is not independent.When the traffic jam occurs at a node in the traffic network,if the traffic jam cannot be evacuated in time,the jam will spread throughout the whole network and then lead to large-scale network congestion.This phenomenon is also described as Cascading failure.The traditional solution is to increase the infrastructure construction,but if there is no corresponding planning and management strategy,congestion alleviation is difficult to achieve the desired effect.Therefore,it is of great significance to analyze the propagation rules of congestion in urban road network and formulate reasonable,effective and widely applicable evacuation strategies to alleviate traffic congestion,so as to improve the traffic distribution efficiency of urban road network.This paper uses complex network theory to establish the topological structure of urban road traffic network,analyzes network characteristics and node relationship establishes a successive congestion model of urban road traffic network,studies the evolution mechanism of successive congestion in the urban road network,and formulates evacuation from the perspective of route guidance.The research work mainly includes the following four aspects:(1)Study on complex characteristics of traffic network and comprehensive importance of nodesBased on the complex network theory,the topological structure of urban road traffic network is constructed.This paper combined the relevant definitions of complex network characteristic parameters,selecting node degree,strength,clustering coefficient and compactness,and used grey system evaluation and analytic hierarchy process(AHP)to construct a network node importance evaluation model.On this basis,in order to analyze the attributes of the network nodes more comprehensively,the time impedance of the node and the distributable load of the node are integrated to establish the node's comprehensive importance index,and the entropy weight method is used to determine the index weight.(2)Construction of successive congestion model of transportation networkThe temporal and spatial distribution and evolution characteristics of successive congestion in the urban road traffic network are analyzed using the CML theory,and the successive congestion model of the urban road traffic network is established for the two situations of frequent congestion and occasional congestion.Calculate the collapse threshold that causes the local collapse of congested nodes,and quantify the scope of diffusion influence in the network after the key nodes of the transportation network are congested under different conditions.The Moran's I index is used to illustrate the impact of congestion on the spatial autocorrelation of urban traffic networks.(3)Construction of a dynamic congestion evacuation model considering the comprehensive importance of nodesAccording to the time-varying characteristics of the traffic network load,a calculation method for node distributable load is constructed.Considering the distributable load constraints and node collapse threshold constraints during the evacuation process,for the two situations of frequent congestion and occasional congestion,a frequent dynamic congestion evacuation model and a sporadic dynamic congestion evacuation model are constructed.Aiming at the proposed evacuation model,based on the Dijkstra algorithm,with the goal of maximizing the comprehensive importance of evacuation route nodes,an optimization algorithm for successively congested evacuation routes in urban road traffic networks is established.(4)Case analysisThe transportation network in the downtown area of Changchun is selected as a case study.First,based on the actual conditions of the road network,the topological structure of the traffic network is analyzed and the complex characteristic parameter values of the network are calculated.On this basis,the node importance of the road network is calculated,and the successive congestion model is used to judge the congestion node and the congestion influence range.Secondly,according to the calculated congestion node and influence range,the dynamic evacuation model is used to evacuate the road network congestion.Finally,considering the scale of different congested nodes,the model and algorithm of this paper are verified.