Analysis & Comparative Study of Reliability & Safety for Various Redundant Computerized Interlocking Systems Based on Continues-time Markov Chains Approach

Articles in Press

Document Type : Original Article

Authors

1 School of Railway Engineering, Iran University of Science & Technology (IUST)

2 Signalling Senior Engineer. Khatam Equipment and Development Company

10.22034/tri.2021.254855.2825

Abstract

Interlocking as a heart of railway signaling system is an important part of this safety-critical system. Looking at the interlocking tasks including correct routing, locking the routes and releasing them timely and commanding to wayside equipment, including signals, point machines and track circuits, will be revealed due to the critical nature of these tasks, interlocking necessarily must have a high tolerance against different probable faults. The best way to design a fault tolerant system is redundancy in processors. Structures with 2 processor units (dual hot stand-by), 3 processor units (3-vote-2 redundancy) and 4 processor units (double 2-vote-2 redundancy) are the most practical techniques which manufacturers have used in the interlocking systems. These redundancies improve reliability, safety and fault tolerancy of system. Each structure has its own advantage. In the Markov method by considering the different states of processors and failure rate, system state diagram is obtained. Then the system transitions between the various operating modes can be expressed by a matrix. The state transition equations formed the behavior of the system to fully assess the safety, reliability and mean time to failure of interlocking system to quantify these indexes. In this article we evaluate and compare the reliability and safety of mentioned structures and study the impact of system parameters (such as failure rate and coverage factor) on the dependability property. We showed that the increasing of coverage factor can straightly improve the safety and also reliability of the system, in addition the control strategy of switch in the hardware of redundant interlocking system is very important in the dependability of this system.

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Main Subjects

Journal of Transportation Research

Articles in Press, Accepted Manuscript
Available Online from 30 June 2021

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