Resource

Railway Signalling Systems

Interlocking systems sit at the heart of safe railway operations — controlling signals, track switches, and route authorisations to prevent conflicts and protect trains. But developing, certifying, and maintaining these systems to the standards modern railways demand is a complex, high-stakes undertaking.

The risk? Interlocking systems that fail to meet the safety, reliability, and availability requirements of the networks they protect — with potentially catastrophic consequences.

The solution: A rigorous engineering approach that integrates RAMS analysis, standards compliance, and systematic safety assessment from the earliest stages of development.

Safe by Design. Reliable by Engineering.

This white paper examines the development of modern railway interlocking systems — from design requirements and system typologies through to RAMS, standards compliance, and the safety assessment process.

What Makes This Approach Different

  • Covers both Computer Based Interlocking (CBI) and Solid State Interlocking (SSI) architectures

  • Integrates RAMS requirements — Reliability, Availability, Maintainability, and Safety — into the design process

  • Applies the full CENELEC standards framework to interlocking development and certification

  • Draws on deep experience in signalling system development across complex rail environments

What's Inside This White Paper

  • How interlocking systems prevent route conflicts and protect train movements

  • The functional scope of a modern interlocking: signals, switches, routes, and beyond

  • Why interlocking systems must meet the highest standards of safety and availability

Types of Interlocking Systems

  • The evolution from relay-based to solid state and computer-based interlocking

  • How Computer Based Interlocking (CBI) systems work and where they are deployed

  • Solid State Interlocking (SSI): architecture, advantages, and operational context

Design Requirements and Engineering Process

  • The functional and non-functional requirements of modern interlocking systems

  • How to structure the development process to meet safety and performance targets

  • Managing interfaces between the interlocking and wider signalling infrastructure

RAMS and Safety Assessment

  • Applying Reliability, Availability, Maintainability, and Safety analysis to interlocking systems

  • How RAMS requirements influence design decisions and architecture choices

  • The safety assessment process and its role in achieving certification

Standards and Compliance

  • Applying CENELEC railway standards to interlocking development and verification

  • The role of EN 50126, EN 50128, and EN 50129 in the certification process

  • How to manage standards compliance across the full system lifecycle

Who Should Read This

  • Signalling engineers working on interlocking development or modernisation

  • Safety and certification leads responsible for CENELEC compliance

  • RAMS engineers supporting signalling system programmes

  • Systems architects designing or integrating railway signalling infrastructure

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