A rapid method for estimating the prevented train delays as an effect of rail infrastructure inspections

In this study, a formula is described for calculating the relationship between preventive maintenance inspections and train delays for rail infrastructure. The reduction in train delays due to preventive maintenance has been calculated as follows: When an inspection is performed, the probability to find a potential failure is between 0 and 100 %. The potential failure is registered as an inspection remark. The risk that the potential failure will degrade to a functional failure within a certain time is also between 0 and 100 %. Strictly speaking, this time is equal to the specified maximum time to restoration in the inspection remark registration, e.g. within one week, but in practice longer. As an example, one can assume 100 inspections, with 10 % probability to find a potential failure, 75 % risk for functional failure if an action is not taken within a near future and 25 % risk for train delays. This gives 100 · 0.1 · 0.75 · 0.25 = 1.875 prevented train-delaying functional failures, and therefore 1.875 times the average number of train delay minutes in reduced minutes of train delays. A case study was carried out to verify the proposed method. The prevented train-delay minutes per maintenance inspection for various rail infrastructure systems were found to be between 0-40 minutes per inspection. However, the result depends to a large extent on the definition of inspection within the maintenance database. The result also depends on the type of inspection, e.g. safety or maintenance inspections. Moreover, the result depends greatly on the criteria that are being used for specifying the risk that a potential failure will degrade to a functional failure within a certain time period. These factors need to be clear before actions are taken upon the results