Assessing An Urban Rail Transit Network Resilience Considering Time-varying Demands

The urban rail transit(URT),as a complex and giant system,plays a huge role in guaranteeing the daily travel of residents and the normal operation of the city.But in practice,all kinds of sudden internal and external disturbance factors,such as flood,signal failure,pose a serious threat to the security and stability of the system performance.Previous studies mainly focused on the static structure of the system,which ignored the system participants which passengers are an important factor.Therefore,considering the time-varying characteristics of passenger travel demand and based on complex network theory,this paper conducted in-depth analysis on the performance changes of URT system under the influence of daily operation failures from the perspective of elasticity and vulnerability.The specific content is summarized as follows:First,the definitions and relationships of the related concepts of transportation system performance are analyzed.And then,from the perspective of system vulnerability,a new system performance analysis method is proposed combining dynamic travel demand and static topology,including the establishment of a URT system delay scenario and disruption type under the daily operation failure,a dynamic identification method of station importance based on accessibility,and an index to measure the vulnerability of URT system which supply can not meet travel demand due to different degrees of operation delay.This method does not need passenger flow distribution,but uses a reasonable path database to characterize passengers’ entry and exit and transfer characteristics conveniently and quickly,so as to explore the impact of travel demand changes on the performance of the URT system.Then,in the identification of the line importanc,it is found that the loop line is a special and important structure in the URT network.From the perspective of system resilience,the influence of loop structure on the disruption and recovery process of URT system is further analyzed based on the improved cascade failure model.In the system disruption stage,the improved coupled image lattice model was used to simulate the cascade failure scenarios of the system at the station and line levels respectively.The node failure ratio,cumulative failure ratio and operational efficiency were used as metrics to analyze the change of system resilience.In the recovery stage,the recovery performance of system resilience is studied by using different station and line recovery sequence.Finally,an empirical analysis of Beijing URT is carried out by using this method.Some important conclusions are found:(1)the importance of stations and lines is different in different time periods,and there are certain changes and distribution rules,which are affected by static topology and dynamic demand.(2)For short-term time delay,the impact of important stations on system performance is nonlinear with the increase of delayed travel demand.For the long-term station delay,the URT system shows different vulnerability in different periods,but it shows exponential decline and heavy tail distribution under the station disruption.In the case of interval continuous interruption,the degradation of system performance is obviously segmented and stratified.(3)When the robustness of the stations on the loop line is improved,the system resilience is improved more obviously,and the disruption of the transfer stations on the loop line has the greatest impact on the system resilience.In addition,loop lines closer to the center are more important than peripheral ones,such as Beijing URT Line2 and Line 10.This thesis provides a reference for rapid identification of important components and measurement of system performance by considering dynamic passenger flow changes,and also provides an important supplement for the corresponding performance metrics system.In addition,it also has a reference significance for many URT systems with loop structure to effectively improve the ability of risk resistance and antidisturbance,and provides an important theoretical basis for the planning,follow-up construction and operation management of the actual URT network.