Railway Infrastructure - Signalling

Understanding Railways Series:

UK Railway Industry for Dummies, focusing on Rail Infrastructure

Railway Infrastructure - Signalling (this post)

  Signalling for Railways 

Historically, trains were operated by a driver who knew a lot about the train, the route, and even the train itself.  Speed, signalling, and braking distance were controlled by the driver, and they had to manage the train, the driving, and the route information affecting them.  Signalling was used to help the driver determine whether the rail line was clear or approaching, when to slow down, and to provide reminders, thereby allowing the driver to control the train safely by managing multiple factors.

Advancements in technology have built on existing infrastructure and approaches, enabling more trains, safer travel, and better information.  For example, wheel counters allowed signalling to ensure that a train and all its wheels have cleared a section.

Telecommunications allow a central control centre (ROC) to communicate with the drivers.  GSM-R...

The train should run regardless of temporary telecommunications issues or unavailability (assuming it is safe).  The onboard computer on every train can provide the driver with information or act on it, such as automatically stopping the train if a red light is detected while the train is on the section of track the driver is entering.  

ETCS is for modern signalling; the fundamental principle is that all trains, routes and tracks can be managed centrally safely (see SIL4).  Everything on the railway has to be safe.  Super safe, if unsure, stop is the principle.

Common Equipment

Balise

A balise is a device mounted on the track between the two rails that sends messages to a train as it passes overhead, primarily conveying the train's position.

Understanding Railways Series:

UK Railway Industry for Dummies, focusing on Rail Infrastructure

Railway Infrastructure - Signalling (this post)

UK Railway Industry for Dummies focusing on Rail Infrastructure

Understanding Railways Series:

UK Railway Industry for Dummies, focusing on Rail Infrastructure (this post)

Railway Infrastructure - Signalling

Rail assets are organised into large, hierarchical asset classes that are interdependent, forming a rail system. These rail assets are organised using detailed, lower-level assets built from taxonomies and ontologies tailored to each jurisdiction within the rail industry.  Railway interaction and asset operations must comply with stringent rail regulations.  Safety has a massive focus.

Taxonomy organises data hierarchically, while ontology models both hierarchies and complex relationships between entities and their properties. In the rail industry, ontologies are crucial for successful asset modelling.

The picture shows examples of significant assets (high-level)

Main Railway Infrastructure Assets high-level overview.

An AI-generated image to explain commonly used railway terms.

The railways consist of "rolling stock, rail infrastructure, and environment"; these components have multiple relationships with one another.

1. Rolling stock is the trains.

2. Rail Infrastructure relates to: 

    2.1. Electrification/power/energy, generally used for power supply for signalling, train power, and telecoms.  Key protocols for using devices are MQTT, MODBUS and IEC

• UK network supplies at 400kV, and train propulsion uses 25kV (AC) for Mainlines and 1-3kV (DC) for requiring step-down.  Train propulsion power is referred to as Traction Power Supply.
• Non-Traction Power Supply, used for signalling, station power, and lighting
  
  
• Overhead Line Equipment (OLE) is critical in railway electrification.  OLE span - Longer spans reduce the number of masts, lowering installation costs—but only if mechanical and electrical limits are respected.
• Overhead Contact System (OCS) or Third Rail: Transfers power to trains.

    2.2. Telecommunication, track-to-control, and train-to-control are used to communicate, including sensors and IoT devices.

    2.3. Signalling relates to ensuring train safety so the train knows there is a train ahead of it, and issues when to slow down.

    2.4. Track Engineering, also known as Rail Engineering and The Permanent Way, involves the rails, connectivity, support, extensive physics and geometry, steel rail installation and joining, ballast (the ground on which the track is laid), drainage, substructure, and sleepers. It gets detailed with rail joins (Fishplated) and even the welding process used.  Fastening types, baseplates, sleepers, off-track maintenance such as hedge trimming (you won't believe the rules unless you work in the rail industry) ...

SCADA systems integrate sensors, Remote Terminal Units (RTUs), Programmable Logic Controllers (PLCs), and Human-Machine Interfaces (HMIs) to collect real-time data, automate processes, and ensure operational safety and efficiency. In rail, SCADA typically manages traction power, station systems, and communications infrastructure.

3. The environment refers to the existing conditions before the railway, including the topography and type of terrain, bridges, and rivers.

The interdependencies with the rail industry are perfect for numerous AI scenarios.  With any AI, you need high-quality data and must secure it appropriately.  Bring information from across business functions together to enable automation, ML, and AI, and support better decision-making.

Each country or jurisdiction has different rules for trains, and operators must comply with Health, Safety, and Environment (HSE) regulations.  There are industry rules adapted to each jurisdiction, and standards vary by region.  For example, most jurisdictions have a gauge width requirement; in the UK, the standard gauge is 4 feet 8 1/2 inches (1435mm).  There are exceptions, such as heritage railways in the UK.  There are manufacturing standards for everything.  EN13674 is the British Rail specification for the actual pure steel used to manufacture the track to be installed.

ISO 55000/1/2 addresses Physical Asset Management.  Building Information Modelling (BIM) enhances the design and construction process, and both apply to Rail Infrastructure.  There is generally a disconnect between Asset Management and BIM, and the International Foundation Modelling (IFC) aims to establish a standardised asset model for the railway industry; we are on v4.3.

SIL4 - Used for critical safety systems such as railway interlocking control systems. Safety Integrity Level is defined in functional safety standards, such as IEC 61508. SIL1 is the lowest level, and SIL4 is the level at which a system has the lowest likelihood of dangerous failure and the highest reliability. 

Understanding Railways Series:

UK Railway Industry for Dummies, focusing on Rail Infrastructure (this post)

Railway Infrastructure - Signalling

References used: 

Permanent Way Institution (2023) Understanding Track Engineering. London: The PWI. Available at: https://www.thepwi.org/product/understanding-track-engineering/ (Accessed: 4 July 2025)

Camarazo, D., Roxin, A. and Lalou, M. (2024) Railway systems’ ontologies: A literature review and an alignment proposal. 26th International Conference on Information Integration and Web Intelligence (iiWAS2024), Bratislava, Slovakia, December 2024. Available at: https://ube.hal.science/hal-04797679/document (Accessed: 4 July 2025).

Network Rail (2021) Asset Management: Weather Resilience and Climate Change Adaptation Plan. London: Network Rail. Available at: https://www.networkrail.co.uk/wp-content/uploads/2021/11/Asset-Management-WRCCA-Plan.pdf (Accessed: 4 July 2025).