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

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journal contribution
posted on 20.09.2017, 09:07 by Sam Bemment, Roger Goodall, Roger Dixon, Christopher WardChristopher Ward
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.

Funding

The authors acknowledge the financial support provided by the United Kingdom EPSRC (Engineering and Physical Sciences Research Council) and the United Kingdom RSSB (Rail Safety and Standards Board) through grant number EP/I010823/1 for the project ‘REPOINT: Redundantly engineered points for enhanced reliability and capacity of railway track switching’.

History

School

  • Mechanical, Electrical and Manufacturing Engineering

Published in

Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit

Volume

232

Issue

5

Pages

1407-1424

Citation

BEMMENT, S.D. ...et al., 2017. Improving the reliability and availability of railway track switching by analysing historical failure data and introducing functionally redundant subsystems. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 232(5), pp. 1407-1424.

Publisher

SAGE Journals (© The authors)

Version

VoR (Version of Record)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution 4.0 International (CC BY 4.0) licence. Full details of this licence are available at: http://creativecommons.org/licenses/ by/4.0/

Acceptance date

23/07/2017

Publication date

2017-09-13

Copyright date

2018

Notes

This is an Open Access Article. It is published by Sage under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/

ISSN

0954-4097

eISSN

2041-3017

Language

en