Modelling maintenance in railway infrastructure management

Conventional railway track, of the type seen throughout the majority of the UK rail network, is made up of rails that are fixed to sleepers (ties), which, in turn, are supported by ballast. The ballast comprises crushed, hard stone and its main purpose is to distribute loads from the sleepers as rail traffic passes along the track. Over time, the stones in the ballast deteriorate, leading the track to settle and the geometry of the rails to change. Changes in geometry must be addressed in order that the track remains in a safe condition. Track inspections are carried out by measurement trains, which use sensors to precisely measure the track geometry. Network operators aim to carry out maintenance before the track geometry degrades to such an extent that speed restrictions or line closures are required. However, despite the fact that it restores the track geometry, the maintenance also worsens the general condition of the ballast, meaning that the rate of track geometry deterioration tends to increase as the amount of maintenance performed to the ballast increases. This paper considers the degradation, inspection and maintenance of a single one eighth of a mile section of railway track. A Markov model of such a section is produced. Track degradation data from the UK rail network has been analysed to produce degradation distributions which are used to define transition rates within the Markov model. The model considers the changing deterioration rate of the track section following maintenance and is used to analyse the effects of changing the level of track geometry degradation at which maintenance is requested for the section. The results are also used to show the effects of unrevealed levels of degradation. A model such as the one presented can be used to form an integral part of an asset management strategy and maintenance decision making process for railway track.