A Petri nets based decision support tool for railway traffic conflicts forecasting and resolution

The full paper describes current results and applications of an ongoing research concerning the operational simulation of complex railway systems based on working criteria and operational rules of interlocking and line signalling systems. Modelling is based on object oriented approach by the Petri nets formalism, that allows high processing openness and modular building without breaking away from the safety systems logic. The development of a full model includes the integration of a Common module to be applied to any layout and interlocking technology, a Timetable module capable to simulate the operational program, a Movement Inspector module to manage traffic priorities automatically and finally a Top Level module where a specific layout and its routes are modelled. The software tool used is a specific software for extended Petri Nets development, validation and simulation (Faber (c)), that allows modularity in Petri nets definition and manages variables and types declaration, being endowed with a C language interpreter. The tool could be used both for regularity forecasting and in decision support systems for the management of conflict resolution. For these goals the model was largely tested on the Roma-Formia railway, an Italian high density traffic line. The tests include simulations of traffic regularity monitoring and forecasting in both un-perturbed and perturbed conditions, by generating delays of sets of trains along the line and by verifying the response of the system in comparison with measured delays.