Towards a fault tolerant railway system

The railway transport system is experiencing an increasing level of traffic demand in terms of both passengers and freight. The 24/7 railway has been stated as a possible solution to satisfy the future growth in demand. However a greater utilisation of the network will accelerate deterioration processes and reduce the time slots for maintenance. In this context the ability of the system to continue operating properly in case of failure is a key factor to provide a safe and reliable service, but the railway system is not currently designed to be fault tolerant. This work is a first attempt to investigate options for exploiting and optimizing the potential of the current infrastructure to provide alternative paths to trains when failures occur or sections of track are taken out for maintenance, thus improving service reliability. This paper presents a methodology based on a whole system approach aiming at evaluating ways in which features of the design, operation and maintenance strategies can provide a fault tolerant railway system. Simulation, optimization and failure modelling techniques will be combined for an integrated assessment of different solutions in order to reveal the most effective railway system. A discrete-event simulation model has been developed to simulate railway operation according to a given timetable and assess system performance for different system designs and failure scenarios. The railway system is modelled as a timed colour Petri net which implements safety, control and dispatching rules in order to manage trains movements through the network. Performance requirements are defined in terms of total delay. Rail operations in a section of the UK network have been simulated for a number of infrastructure and failures scenarios, and results show a positive effect of additional switches on service reliability.