Vulnerability Study In Complex Bilayer Network Of Urban Public Transport Under Rainstorm Extreme Weather

Public transport is an important part of urban transport and bears the daily travel needs of a large number of urban residents.However,in recent years,extreme weather,especially rainstorms and snowstorms,have frequently occurred in many cities,causing detrimental effects on the urban public transport system(UPTS).The UPTS usually operates stably,but in extreme weather,part of stops(stations)and lines in the system will fail and cannot provide passenger transport services due to water logging or snow,resulting in the transfer of passengers to other stops(stations)and lines,which may eventually lead to the cascading failures of stops and lines and collapse of the whole system.In order to study the dynamic changes of UPTS under extreme weather,this paper takes rainstorm as an example to analyze the mechanism of the impact of extreme weather on UPTS,and researches the relationship between rainstorm intensity and traffic flow.Secondly,according to the theory of complex network modeling,the conventional ground bus and metro subsystems are abstracted into a Bus-Metro Complex Bilayer Network(Bus-Metro CBN).Based on the Couple Map Lattices(CMLs)model,a cascading failure model of nodes and edges in Bus-Metro CBN is proposed,and the passenger flow transfer rules under node and edge failures are established.Thirdly,this paper uses the terminology of vulnerability to describe the adverse effects of extreme weather on UPTS.From the perspectives of network topology and passenger transport function,the loss rate of the node scale in the maximum connecting subgraph,the whole network efficiency and the passenger volume are selected to synthesize a vulnerability operator.Based on this operator,the vulnerability of UPTS under extreme weather can be quantitatively calculated.Finally,taking the UPTS in the old urban area of Xi'an as an example,the cascading failure process of the UPTS under rainstorm extreme weather are simulated by MATLAB.Through the simulations,this paper finds that the Bus-Metro CBN may experience a secondary failure process due to the capacity of nodes and edges.There is a rainstorm intensity threshold(s(28)1.80,h(28)90 mm/24h)that causes the network to collapse.At the same time,the increase of the nodes and edges capacity can reduce the vulnerability of CBN,and the optimal nodes and edges capacity is 1.4 times of their initial load.In addition,network vulnerability analysis shows that the reduction of node coupling strength has more potential in reducing network vulnerability than the reduction of edge coupling strength.In most scenarios(17 scenarios/ a total of 20 scenarios),the vulnerability of the Bus-Metro CBN mainly comes from the reduction of the whole network efficiency,and the improvement of emergency response capability of key nodes and edges is better than capacity improvement in reducing network vulnerability.This article enriches the related researches on vulnerability of urban public transport network,promotes the development of multi-layer transport network modeling,provides a new method for introducing disturbance variables of natural disasters such as rainstorm,and provides an analytical basis for public transport management departments to formulate emergency trategies under rainstorm extreme weather.