Assessing The Vulnerability Of Urban Rail Transit Network Under Dynamic Restriction

In the urban transportation system,rail transit meets the massive travel needs of urban residents,and has become the main mode of travel for urban residents.In recent years,many cities have frequently experienced heavy pollution such as smog.In order to improve urban air quality,in China,many cities have implemented One-Day-Per-Week(ODPW)and Odd-And-Even(OAE)vehicle dynamic restriction policies according to the degree of weather pollution reduce exhaust emissions.The implementation of the vehicle restriction policy has caused some travelers who travel by private cars to change their travel methods and instead take subways and other rail transits,which has brought tremendous pressure to the rail transit network.Under normal circumstances,the passenger flow of the rail transit network is stable,and there are few passenger flow changes.After the vehicle restrictions are implemented,part of the passenger flow will be transferred from the road to the subway and other rail transit,causing the rail transit network to be affected by a large number of passenger flows.Some stations have been suspended due to overload failure,which in turn caused station cascading failure,reducing the operational efficiency of the entire rail transit system.In order to analyze the dynamic changes of the urban rail transit network(RTN)under dynamic restriction policies,first,this paper abstracts the urban RTN into a complex network based on the complex network modeling theory.Secondly,a cascading failure model of complex network nodes based on load capacity model is proposed and established the rules of passenger flow transfer under the node failure scenario.Thirdly,the vulnerability is used to reflect the adverse impact of dynamic restriction policies on urban RTN.From the aspects of complex network topology and passenger transport functions,the average shortest path,congestion degree,and average passenger flow intensity are selected to construct an RTN’s vulnerability assessment index,based on this,the generation and change rules of RTN’s vulnerability under dynamic traffic restrictions are quantitatively analyzed.Finally,taking the subway system in Xi’an as an example,the cascading failure process of urban RTN under dynamic restrictions was simulated based on simulation technology.The simulation results show that,inconsideration of the node capacity,after implementing the vehicle dynamic restriction policy,the cascading failure will occur in the urban rail transit complex network;and the node capacity is the main factor affecting the vulnerability of the complex network of rail transit.Increasing the node capacity can effectively reduce the vulnerability of the complex network of urban rail transit.At the same time,it was found that when the restriction policy was changed from ODPW to OAE,RTN was more likely to cause cascading failures,and its vulnerability increased sharply.This also confirmed that the more passenger flow impacts,the larger the difference between the actual load and the node capacity,the more serious the cascading failure process of the complex network of urban rail transit.This article introduces the influencing factor of passenger flow,expanding the research scope of the factors affecting the vulnerability of urban rail transit complex network,and adds the traffic policy of vehicle dynamic restrictions to urban RTN cascades for urban traffic management departments to prevent and control dynamic restrictions.Failure provides theoretical guidance and policy basis.