Rail Safety Principles. Issues and Perspectives

The safety of all transport systems is based on two main principles: control of the energies involved (in particular the risks of explosion of on-board energy, or loss of a component during trajectory) and control of the trajectory (avoiding collision with another convoy, or with nearby buildings or installations).

The replacement of steam locomotives by thermal and then electric locomotives has enabled us to keep energy risks under control, even if the risk of a train catching fire is still a major issue. The integrity of the convoy's mechanical guidance (rails and switches for the infrastructure, wheels or axles for the convoys) is an absolute imperative: failure leads to extremely violent impacts due to the mechanical energies involved.

Trajectory control is a second fundamental challenge. As rail is a one-dimensional guided mode, the crew cannot change its trajectory to avoid a collision: it can only anticipate it by braking. Timely detection of the risk of collision is not always consistent with the stopping distances of several hundred meters (particularly for curved tracks or in poor weather conditions), the consequence of the low friction of the wheel-rail contact. That's why the rail system pays particular attention to detailed planning of movements to avoid intersecting trajectories between trains, and has developed train spacing techniques to guarantee sufficient stopping distances. This is complemented by strict procedures for signalmen and drivers, and the development of real-time communication technologies to transmit warnings to the driver even before he can see the danger for himself.

The railway system is also highly vulnerable to intrusions on its infrastructure, whether by vehicles not stopping at a level crossing, by agricultural or construction machinery in the immediate vicinity of the tracks, or by geological or atmospheric events damaging the infrastructure (flooding, landslides), which cannot always be detected before the train passes.

The behavior of local residents and passengers is a growing concern in terms of both trespassing and malicious acts.

Finally, the widespread use of digital technologies increases the risk of electromagnetic interference between power circuits and high-frequency digital networks, and of cyber-attacks affecting key components.

The physics of the railway system form the basis of its safety principles; while decelerations during braking are modest, interactions between rolling stock and infrastructure very frequently give rise to vertical and transverse accelerations of several g, which can lead to plastic deformations or wheel/rail guidance failure phenomena, with considerable consequences due to the energies released....