Original Article An optimal age–usage maintenance strategy containing a failure penalty for application to railway tracks Mahmood Shafiee 1 , Michael Patriksson 2 and Stefanka Chukova 3 Abstract Railway track maintenance plays a key role in enhancing the reliability and safety of railway transportation, as it reduces the potential risks of defects and derailments. A railway track degrades over time, due to its cumulative usage (in terms of million gross tons) that results from traffic movements. When the cumulative usage reaches a failure threshold, the railway track breaks and has to be replaced with a new section. Moreover, the infrastructure owner charges the maintenance agent a specific penalty due to traffic disrruption and passenger dissatisfaction. To avoid such costly defects, the railway tracks must be preventively replaced at regular time intervals. In this paper, we propose an optimal bivariate (age–usage) maintenance strategy for railway tracks such that the average long-run maintenance cost per unit time is minimized. The proposed model is applied to 60E1 track on a small part of the Swedish heavy haul line ‘Malmbanan’, and the results are compared with two conventional age-based and usage-based maintenance policies. The results show that the proposed maintenance policy has a substantial potential to reduce the servicing costs of railway track maintenance. Keywords Railway track, million gross tons (MGT), age-based PM, usage-based PM, failure penalty Date received: 20 November 2013; accepted: 23 April 2014 Introduction Along with an increase in railway traffic, investments in rail infrastructure have grown significantly during the last decade. However, high operation and main- tenance (O&M) costs act as a barrier to achieving a favourable financial performance of railway oper- ations. For instance, Sweden has a railway network of 13,000 km of track (the 20th largest in the world) that is spread over wide geographical areas. The investment in Swedish rail infrastructure in 2011 increased by 15% compared with 2010. 1 Despite this, a recently conducted study at Trafikverket (the Swedish Transport Administration) indicated that the O&M cost comprises a major share of the infrastruc- ture’s lifecycle cost (31%), 2 and it also increases annually by SEK 2 billion. 3 Nowadays, rail infrastructure owners are under increasing pressure to reduce their O&M cost while maintaining reliability targets. Rail-track mainten- ance plays a key role in enhancing the reliability and safety of railway transportation, as it reduces the potential risks of defects and derailments. Generally, railway track defects result from a degradation process that usually occurs as different forms of wear, corrosion, erosion, fatigue and crack gener- ation. 4 Any of these forms or their combination can become a cause of a rail break. Rail degradation is a very complex process as it depends on various factors such as: traffic density, axle load, rail-track age, rail material, track geometry, curvature, speed, and accumulated million gross tones (MGT). 5 The degradation of rail tracks may result in substantial replacement costs for the infrastructure owner if it is not prevented in an efficient way. Moreover, it may cause accidents, 6 traffic disruption and ultimately passenger dissatisfaction. Hence, the infrastructure owner may consider charging the 1 School of Applied Sciences, Cranfield University, UK 2 Department of Mathematical Sciences, Chalmers University of Technology and University of Gothenburg, Sweden 3 School of Mathematics, Statistics and Operations Research, Victoria University of Wellington, New Zealand Corresponding author: Mahmood Shafiee, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire MK43 0AL, UK. Email: m.shafiee@cranfield.ac.uk Proc IMechE Part F: J Rail and Rapid Transit 0(0) 1–11 ! IMechE 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0954409714543337 pif.sagepub.com