Research On Resilience Assessment Method Of Communication-Based Train Control System In Urban Rail Transit

Urban rail transit is an effective solution to urban congestion because of its advantages of rapidity,safety and large capacity.As an advanced signaling system,Communication-Based Train Control(CBTC)system is the basis of safe and efficient operation of rail transit.The failures of CBTC system often cause disorder of trains and affect passengers'travel.The severity of failure impacts is closely related to various design and management factors,such as line types,train operation plans,signaling degrade modes,corrective maintenance management,dispatcher strategies,and so on.Therefore,the system performance can vary widely in the failure disposal stage and operation recovery stage.In order to minimize the operational impacts of CBTC failures and further optimize its design,it is meaningful to model and measure the changes of system performance accurately after failure occurs.Nowadays,the most related system properties used in signaling engineering are RAMS(Reliability,Availability,Maintainability,Safety),which can only specify the statistical characteristics of the number and duration of failures under certain conditions.It is difficult to reflect the continuous changes of failure impacts with these existing indicators.To address the problem of insufficient indicators of failure impacts,this paper introduces resilience as the indicator to reflect the dynamic changes of system performance.The main innovations are as follows:(1)The definition of CBTC system resilience is proposed.The interaction model of CBTC system during the conversion process of control levels is established.According to the variation of line operation efficiency in the conversion process,the resilience of CBTC system is introduced as the comprehensive ability to absorb failures,adapt itself to failures,and recover from failures.The influencing factors of resilience characteristics are analyzed.And the general resilience assessment framework of CBTC system is proposed to achieve quantitative assessment.(2)Performance-Based Resilience Assessment for CBTC System(PRAC)is proposed to assess the impacts of signaling failures on system operation efficiency.Three indicators of system performance are selected from technical dimension and organizational dimension.Based on the train tracking model,the calculation methods of the indicators are put forward as well as the corresponding resilience calculation methods.Taking the typical failure scenario of CBTC system as an example,the comparative study of the indicators is carried out.The results show that PRAC method can measure the changes of impacts clearly with train arrival interval indicator.In addition,a rail transit operation simulation platform is designed and built to inject signaling failures,simulate failure scenarios and assess system resilience.(3)Structure-Based Resilience Assessment for CBTC System(SRAC)is proposed to assess the impacts of system structure changes on system performance.The CBTC network is established with equipments as nodes and information flows under different control levels as edges.The reachability of the specified paths is taken as the characteristic of network topology,and the event-driven approach is used to describe the changes of network performance,so as to complete the SRAC.Then the real CBTC network is established,and the characteristics of the network structure are analyzed with Pajek,such as scale-free.Finally,the operation disturbance caused by CBTC system failure is taken as an example,in which PRAC and SRAC are used to assess the failure impacts.The assessment results show that both methods can reflect the changes of failure impacts,show the key links of failures and verify the improvement suggestions for the key links.While both methods are feasible and effective,PRAC is suitable for the validation of recovery strategies,and SRAC is suitable for the evaluation of system equipment layout.