EXPERT GUIDE

How to successfully migrate existing interlocking systems to an open signaling solution

Aging relay-based systems are nearing their limit. Spare parts are scarce, costs are rising, and critical knowledge is fading fast. This guide shows you how to take control of your infrastructure’s future – by migrating to open, COTS-based signaling systems in a step-by-step, low-risk way.

Backed by real-world case studies like the Stockholm Metro, and trusted by leading European operators, this guide gives you the tools to modernize with confidence.

In this guide you will learn:
  • Why now is the time to migrate – and what’s at risk if you wait
  • The 3-step process for safe, incremental migration using digital twins and formal methods
  • How to avoid vendor lock-in while improving safety, control, and scalability
  • How to simulate and verify upgrades before deployment
  • Tools and best practices to minimize disruptions and shorten project lead times
  • Real outcomes from a successful migration at Stockholm Metro (SL)
Migrate existing interlocking systems guide

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Table of Content

  1. Introduction

  2. The need for migrating old signaling systems to
    modern open solutions based on COTS hardware

    The purpose of the migration
    Widespread use of old interlocking systems across Europe
    What’s preventing migration?
    What is the value of migration?

  3. How to migrate old signaling systems to modern
    open signaling solutions based on COTS hardware

    A description of the signaling system
    Introduction to the migration process
    Purpose and effects of the migration process
    The components of the migration process
    Process for migration
    Create digital twins
    Specification of the system and subsystems
    Process for upgrading
    Safety assurance and approval
    Other processes

  4. Case: Stockholm Metro (SL)

    Solution approach
    Outcome and benefits

  5. Your first step toward a migration project

Introduction

Why legacy signaling systems must evolve – and how to do it without disruption

Migrate existing interlocking systems

As railway infrastructure ages across Europe, operators face a critical inflection point. Relay-based signaling systems, some nearly a century old, continue to direct train movements faithfully across thousands of kilometers of track. Yet beneath this reliability lies a growing challenge: the expertise to maintain these systems and access to spare parts needed to repair them.

This guide offers a practical roadmap for infrastructure managers to navigate the increasingly urgent transition from legacy signaling systems to modern, open solutions based on commercial off-the-shelf (COTS) hardware. You’ll discover how digital twins, formal methods, and structured migration processes can transform this complex challenge into a strategic opportunity that will enhance safety, reduce long-term costs, and the possibility to break free from vendor lock-in without disrupting your operations.

Whether you’re planning a complete system overhaul or taking incremental steps toward modernization, this guide provides the framework and real-world examples needed to secure your railway’s signaling future in an increasingly digital world.

The need for migrating old signaling systems to modern open solutions based on COTS hardware

Relay-based signaling systems have long been the backbone of railway operations. While experts predict these systems will remain in use far beyond 2030, a growing challenge is emerging: relay expertise and spare parts are rapidly disappearing. Many organizations face a critical knowledge gap, with limited documentation and resources. This is one of the main drivers for the need to start planning a migration project. Without action, the risk of losing essential know-how increases over time.

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