Improving the reliability and availability of railway track switching by analysing historical failure data and introducing functionally redundant subsystems

Abstract

Track switches are safety critical assets that not only provide flexibility to rail networks but also present single points of failure. Switch failures within dense-traffic passenger rail systems cause a disproportionate level of delay. Subsystem redundancy is one of a number of approaches, which can be used to ensure an appropriate safety integrity and/or operational reliability level, successfully adopted by, for example, the aeronautical and nuclear industries. This paper models the adoption of a functional redundancy approach to the functional subsystems of traditional railway track switching arrangements in order to evaluate the potential increase in the reliability and availability of switches. The paper makes three main contributions. First, 2P-Weibull failure distributions for each functional subsystem of each common category of points operating equipment are established using a timeline and iterative maximum likelihood estimation approach, based on almost 40,000 sampled failure events over 74,800 years of continuous operation. Second, these results are used as baselines in a reliability block diagram approach to model engineering fault tolerance, through subsystem redundancy, into existing switching systems. Third, the reliability block diagrams are used with a Monte-Carlo simulation approach in order to model the availability of redundantly engineered track switches over expected asset lifetimes. Results show a significant improvement in the reliability and availability of switches; unscheduled downtime reduces by an order of magnitude across all powered switch types, whilst significant increases in the whole-system reliability are demonstrated. Hence, switch designs utilising a functional redundancy approach are well worth further investigation. However, it is also established that as equipment failures are engineered out, switch reliability/availability can be seen to plateau as the dominant contributor to unreliability becomes human error.

On the Fault Detection and Diagnosis of Railway Switch and Crossing Systems: An Overview

“…fault during the maintenance process such as a lack of lubrication, improper tampering, or loose fasteners can lead to failure of the S&C system [50,51]. The environmental conditions, such as snow, rain, or obstruction on the track, have an important role in the failure of some components of S&C systems.…”

Prediction of railway switch point failures by artificial intelligence methods

“…In the case of failures that have occurred, the solution time of the failure can be shortened by obtaining information about the root cause of the failure and the railway operation can be returned to its normal course with minimum interruption. Statistical analysis, classification, and model-based methods are used in the literature to evaluate data related to failures and to make predictions [2][3][4]. In particular, classification methods are frequently used in the detection of railway failures [2].…”

Model-Based Controller Design for a Lift-and-Drop Railway Track Switch Actuator

“…A new generation of track switching concepts are emerging from projects such as S-code [1], In2Rail [2] and REPOINT [3]- [4]. improving rail network performance.…”

“…It also has a new mechanical design that incorporates a lift-and-drop switching mechanism replacing the sliding motion that exists today. This design presents benefits in switch reliability, ease of maintenance and increased rail capacity detailed in [3]. In Fig.…”