Impact of signalling and automation failure modes on railway operation: assessment by simulation

The dependability or RAM (Reliability, Availability and Maintainability) parameters are the most important elements that allow to estimate the Life Cycle Cost (LCC) of a system and to forecast performances during operating conditions. In the field of railway transportation, conventional measures, such as the mean delay of the train, or the Service Dependability (SD), can be profitably used to estimate the overall system behaviour taking into account the presence of failures. In this paper the authors present a new methodology, fully implemented in the Excel environment, for estimating the Service Dependability of a railway system. In particular the authors analyse the failure modes impact of an innovative signalling system (ERTMS level 2) on train operation in a typical lay-out for high speed railway lines, as far as scheduling fulfilment only is concerned. Starting from the reliability characteristic of the single items, the failure mode occurrence times are generated by means of a Monte Carlo procedure, already utilised by the authors in similar applications. The joint use of a general purpose traffic simulator allows then to evaluate the effect of failures on the travelling time, and the results collected during the simulations are statistically post-processed in order to estimate, for the failure modes analysed, the probability behaviour of the delay occurrence.