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.