Next Stop: Railway Interlocking Systems

October 24, 2019

Interlocking systems play an important role in keeping railways safe. Learn how Critical Software works on ensuring trains reach their destinations safely, from developing high-quality software to providing comprehensive system certification.

train tracks with train passing by

You’re sitting comfortably on the train, probably looking out the window admiring the landscape or just reading a good book. What usually doesn’t cross your mind is the complex network of people and systems that make your journey possible. Journey with us as we discover what does on behind the scenes.

One of the most crucial components of train travel is the interlocking system. To put it simply, its main job is to ensure safe train operations by preventing route conflicts while controlling external objects such as signals and track switches. These systems' response time is within milliseconds!

The most commonly used system today is the Computer-Based Interlocking (CBI) system, which possesses at a very high capacity, uses compact equipment, is flexible and achieves an excellent performance. Because every railway system has its own requirements, the interlocking systems must be very flexible. For this reason, they use a modular architecture – centralised or distributed - that allows them to interact with all kinds of different equipment depending on the needs of a specific network.

With such a safety-critical job, these systems must meet strict international standards to guarantee the highest levels of safety, reliability and availability. In this sense, hardware and software is subject to rigorous verification and validation processes, conducted by independent test teams, where all possible hazard situations must be identified. Qualitative and/or quantitative methods (usually a combination of both) are employed. Questions such as "what must go wrong for a system hazard to occur?" are looked at from a qualitative perspective, while quantitative methods focus on providing estimates of probabilities, rates and/or severity of consequences to the operation.

Many items are mandatory for the assessment of these critical systems, such as: the preparation of safety cases, technical safety reports, safety management (including the preparation of safety plans, hazard logs and safety requirements specifications), evidence of quality management throughout the system’s lifecycle and evidence of functional and technical safety.

Critical Software is involved in a set of certification programs for several Computer-Based Interlocking systems. Trains in countries such as Germany, France, Austria, Italy and Israel are relying on software developed by our engineers who work behind the scenes to develop and implement these systems, ensuring we all arrive safe and sound to our final destinations!

If you are interested in learning more about the architecture and design requirements of modern interlocking systems check out our white paper.