Avoiding Deadlocks in Synchronous Railway Simulations

A deadlock is a situation in which a number of trains cannot continue along their path at all because every train is blocked by another one. In practical railway operation, dead-locks are avoided by the timetable and, in case of delay, by dispatching decisions of hu-man traffic controllers. Avoiding deadlocks is also an essential feature of software sys-tems for railway simulation. In simulation systems that follow the asynchronous principle, deadlocks will not occur since all conflicts are solved by rescheduling. In synchronous simulation systems, a positive strategy against deadlocks does not yet exist. The control logic of existing systems can only avoid simple forms of deadlocks. However, traffic simulation on critical infrastructures with a high probability of deadlocks is still a prob-lem. The paper describes two principles of how deadlock avoiding rules could be inte-grated in the control logic of synchronous simulation systems and discusses the pros and cons of these two approaches.