For more than a century railway signalling systems have been evolving and including new equipment in order to provide safer and more controlled means of train operation. With the introduction of Information and Communication Technologies (ICT) (eg fibre optics, GSM-R), signalling systems can implement functionalities to achieve higher levels of control and safety.

Modern Train Control Systems (eg ERTMS, PTC, CBTC) integrate signalling functionalities with extended capabilities such as automatic authority management, enhanced traffic control, train scheduling facilities, driving assistance, asset protection etc. These new applications allow rail operators to maximise the capacity of railway lines and improve business processes.

Nevertheless, the fundamental purpose of any Train Control System is to prevent train collisions and derailments. The degree of safety in a system is based on how well the system avoids accidents. In a safe system, an accident will never occur.

Initially, in the absence of any signalling, the safety of train movements was entrusted to controllers, drivers and maintainers; and accidents were mainly attributable to human error factors.

However, new technologies have allowed the development of systems with inherit safety, thereby minimising the impact of human factors during system operation. Automatic train routing or driverless applications are the ultimate proof of this trend.

In the new environment, the safety of railway operation relies on system design, implementation and testing processes. Signalling devices are to be designed failsafe, meaning that any failure of a device will lead to the safest state. Specific techniques are applied to designing and writing of the software controlling safety critical functions. Double chains, independent verifications, extensive simulations and infield testing are essential to provide the proper level of safety for a Train Control System.

If the availability of a safe system is compromised, degraded modes of operation are implemented, and a driver, a controller or a maintainer shall assume part of the responsibility over train movements.

Hazard analysis during the designing and testing phases, and prior to the commissioning of a railway system are mandatory. It must identify the operational risks and the associated procedures to mitigate those risks, in both nominal and degraded modes of operation. In a modern Train Control System, the mitigation of risk is mostly covered  by the system itself, and when this is not possible, they must never rely on a single individual and must have procedures involving double confirmation by two individuals.

Railway operators and engineers must work side by side so as to deploy modern Train Control Systems and operational rules consistently over rail networks with the aim of not only avoiding accidents, but also to ensure that a human error of a controller, driver or maintainer will never have disastrous consequences.