Towards a Fault Tree Analysis of Moving Block and Virtual Coupling Railway Signalling Systems

Railway systems are complex given their interconnectivity with sub-systems wherein each contains multiple components. Virtual Coupling (VC) is a next-generation railway signalling technology that advances Moving Block (MB), also known as European Train Control System Level 3 (ETCS L3). Some pilot implementations exist for MB. However, VC is still a visionary system and involves several safety issues due to the relative braking distance between trains. Therefore, it is important to evaluate the safety of this system to understand whether it is feasible for deployment. This paper performs a preliminary safety and reliability study by introducing a fault tree (FT) model to investigate the possible causes that lead to an unsafe train movement for MB and VC. To this aim, a FT model is initially built for the MB system, considering the system configurations and interactions between wireless devices, onboard and trackside equipment. Then, the FT model of the VC system is derived on top of the one for MB and the differences are highlighted between the FT elements of the two systems.