Analysing an autonomous tramway positioning system with the Uppaal Statistical Model Checker

The substitution of traditional occupancy detecting sensors with an Autonomous Positioning System (APS) is a promising solution to contain costs and improve performance of current tramway signalling systems. APS is an onboard system using satellite positioning and other inertial platforms to autonomously estimate the position of the tram with the needed levels of uncertainty and protection. However, autonomous positioning introduces, even in absence of faults, a quantitative uncertainty with respect to traditional sensors. This paper investigates this issue in the context of an industrial project: a model of the envisaged solution is proposed, and it is analysed using Uppaal Statistical Model Checker. A novel model-driven hazard analysis approach to the exploration of emerging hazards is proposed. The analysis emphasises how the virtualisation of legacy track circuits and on-board satellite positioning equipment may give rise to new hazards, not present in the traditional system.