Deadlock Avoidance and Detection in Railway Simulation Systems

Avoiding or preventing deadlocks in simulation tools for train scheduling remains a critical issue, especially when combined with the objective of minimizing, e.g., the travel times of the trains. In this paper, we revisit the deadlock avoidance and detection problem, and propose a new deadlock avoidance algorithm, called DEADAALG, based on a resource reservation mechanism. The DEADAALG algorithm is proved to be exact, i.e., either detects an unavoidable deadlock resulting from the input data or provide a train scheduling thanks to the scheduling algorithm, called SIMTRAS, which is free of deadlocks. Moreover, we show that the SIMTRAS algorithm is a polynomial time algorithm with an O(|S|× |T |2 log |T |) time complexity, where T is the set of trains and S is the set of sections in the railway topology. Numerical experiments are conducted on the VancouverCalgary single-track corridor of Canadian Pacific. We then show that the SIMTRAS algorithm is very efficient and provides schedules of a quality that is comparable to those of an exact optimization algorithm, in tens of seconds for up to 30 trains/day over a planning period of 60 days.