Rail signalling equipment plays an essential role in keeping the railway operating safely and efficiently.
From detecting trains and controlling their movements to protecting electrical connections and housing specialist signalling equipment, a wide range of systems and components work together as part of the wider railway signalling infrastructure.
Much of this equipment is installed at the trackside, where it needs to operate reliably in demanding environments and, in many cases, remain in service for many years.
But what equipment is actually used in railway signalling, what does each type do, and how do the different components work together?
This guide explains the main types of rail signalling equipment and where they fit into the wider signalling system.
What is rail signalling equipment?
Rail signalling equipment is the collection of systems, components, electrical equipment and protective enclosures used to support the safe control and operation of railway traffic.
The exact equipment required depends on the signalling system, railway infrastructure and application.
Some equipment is responsible for detecting where trains are. Other equipment processes information, controls signalling functions or provides the connections between different parts of the system.
There is also a significant amount of supporting infrastructure needed to protect and house this equipment.
This can include:
Specialist signalling components
Together, these form part of the physical infrastructure that allows railway signalling systems to operate.
What are the main types of railway signalling equipment?
Railway signalling is made up of many different technologies and components. While individual projects can vary considerably, the equipment can broadly be grouped according to the function it performs.
Train detection equipment
Before a signalling system can control train movements, it needs to know where trains are on the railway.
Two established methods of train detection are track circuits and axle counters.
Track circuits
Track circuits use the rails as part of an electrical circuit to detect whether a section of track is occupied by a train.
When a train enters the section, its wheels and axles alter the electrical circuit, allowing the signalling system to determine that the section is occupied.
Axle counters
Axle counters detect trains by counting the axles entering and leaving a defined section of track.
The system compares the number of axles entering with the number leaving. This allows it to determine whether the section is clear or occupied.
The two technologies have different characteristics and applications, and the choice depends on the requirements of the railway and signalling project.
Read more: Axle Counters vs Track Circuits – Which Rail Detection System Is Better?
Signalling interlocking equipment
Interlocking is another fundamental part of railway signalling.
Its purpose is to prevent conflicting routes from being set at the same time and to ensure that signalling commands are carried out in a safe sequence.
Two technologies commonly encountered in modern railway signalling are:
SSI – Solid State Interlocking
CBI – Computer Based Interlocking
Although both perform interlocking functions, they use different technologies and architectures.
Read more: SSI vs CBI – Understanding the Difference Between Railway Interlocking Systems
Signalling location cases
Railway signalling equipment often needs to be installed close to the railway itself.
Signalling location cases provide a secure and protected enclosure for electrical and signalling equipment installed at the lineside.
They can contain equipment such as relays, terminals, power supplies and other components associated with a signalling system.
The enclosure needs to protect the equipment from the external environment while also providing suitable access for installation, inspection and maintenance.
The design of a location case will depend on the equipment it needs to accommodate and the requirements of the particular installation.
Explore: Railway Signalling Location Cases
Trackside Connection Boxes
Trackside Connection Boxes, sometimes referred to as Dis Boxes, provide a protected location for electrical connections associated with railway signalling and other trackside equipment.
They can be used where signalling cables need to be terminated, connected or distributed at the lineside.
Applications can include connections associated with:
Axle counters
Level crossings
Signalling equipment
Trackside electrical systems
Other lineside equipment
As these boxes are installed in exposed railway environments, their construction and protection are important considerations.
The enclosure needs to provide appropriate protection for the connections inside while allowing equipment to be installed and maintained efficiently.
Explore: Trackside Connection Boxes
Signalling equipment racks
Signalling equipment racks provide a structured way of mounting and organising signalling equipment.
Rather than installing individual components without a defined framework, equipment racks provide a purpose-designed structure that can accommodate the equipment required for a particular installation.
Depending on the application, racks can be designed for equipment associated with:
Relay-based signalling
Computer-based interlocking
Signalling control systems
Other specialist railway signalling equipment
Rack configurations can vary depending on the equipment being installed, the available space and the requirements of the project.
For more complex projects, bespoke rack designs can provide a practical way of accommodating specific equipment arrangements.
Explore: Signalling Equipment Racks
Relocatable Equipment Buildings (REBs)
Some railway signalling equipment requires considerably more space than can be provided by a lineside cabinet or location case.
A Relocatable Equipment Building (REB) provides a larger enclosed space for housing railway signalling and associated equipment.
REBs can be used to accommodate equipment such as:
Signalling systems
Interlocking equipment
Power equipment
Communications equipment
Control equipment
Associated electrical systems
One of the benefits of an REB is that much of the building and equipment installation can be prepared away from the railway before being delivered to site.
This can help reduce the amount of work required in a live railway environment.
The design of an REB can also be tailored to the equipment and requirements of an individual project.
Read more: What Is a Relocatable Equipment Building (REB) in Rail Infrastructure?
Explore: Railway REBs
Signalling connection and wiring equipment
Railway signalling systems rely on a large number of electrical connections.
These connections need to be secure, organised and protected, particularly where equipment is installed at the trackside.
A range of specialist components can therefore be used as part of signalling installations.
Plug couplers
Plug couplers provide a means of connecting railway signalling equipment and circuits.
They can allow equipment to be connected and disconnected while maintaining an organised and repeatable installation.
Component boards
Component boards provide a structured way of mounting and connecting signalling components within equipment.
They can help keep wiring organised and make individual components more accessible for inspection and maintenance.
Terminal block covers and Magshields
Terminal block covers, including Magshields, provide protection around exposed electrical connection points.
These types of components may appear relatively small compared with a location case or REB, but they form an important part of the wider signalling installation.
Explore: Railway Signalling Components
Signal control equipment
Railway signalling systems also use specialist components to control or modify signalling functions.
One example is the Signal Aspect Flashing Relay (SAFR).
A SAFR is used in signalling applications where a flashing signal aspect is required.
Specialist equipment such as this can provide a defined signalling function without necessarily requiring a complete change to the wider signalling arrangement.
Explore: Signal Aspect Flashing Relay (SAFR)
Functional Supply Points
Railway signalling equipment also requires reliable electrical power.
Functional Supply Points (FSPs) are used to provide electrical supplies to railway signalling and associated equipment.
Different FSP configurations are available for different applications, which means selecting the appropriate type depends on the requirements of the installation.
The FSP01, FSP02, FSP03 and FSP04 configurations each have different functions and applications.
Read more: FSP01, FSP02, FSP03 or FSP04 – What’s the Difference?
How does railway signalling equipment work together?
Individual pieces of signalling equipment don’t operate in isolation.
They form part of a wider system in which information is detected, processed and used to control railway movements.
A simplified example might look like this:
Train detection → Interlocking → Signalling control → Trackside equipment → Electrical connections → Power supply
A train detection system identifies whether a section of railway is occupied.
That information is passed to the relevant signalling and interlocking systems, which determine what routes and movements can safely be permitted.
The resulting signalling commands are then communicated to the appropriate trackside equipment.
Behind this process is a network of cables, connections, power supplies, equipment housings and other infrastructure that allows the signalling system to function.
The exact arrangement varies depending on the signalling technology and railway application.
Where is rail signalling equipment installed?
Rail signalling equipment can be found throughout the railway infrastructure.
Depending on the equipment and application, it may be installed:
Along the trackside
At railway junctions
At stations
Around level crossings
Within signalling locations
Inside equipment buildings
Within railway control and signalling rooms
Adjacent to specialist trackside equipment
The installation environment can have a significant influence on the type of equipment and enclosure required.
Equipment installed directly at the lineside, for example, needs to be designed with the external environment and accessibility in mind.
What should you consider when selecting signalling equipment?
Selecting railway signalling equipment isn’t simply a case of choosing a product with the right dimensions.
The equipment needs to be suitable for the application, installation environment and wider signalling system.
Standards and approvals
Railway projects can have specific standards, specifications and approval requirements.
Where applicable, project teams may need to consider requirements such as Network Rail standards, product approvals and PADS registration.
The relevant requirements depend on the individual product and application.
Environmental conditions
Trackside equipment can be exposed to:
Rain and moisture
Temperature changes
Dust and dirt
Corrosive environments
UV exposure
Physical impact
Enclosures and equipment therefore need to provide appropriate protection for their intended environment.
Available space
Space can be restricted in railway environments.
The equipment housing or rack may need to fit within an existing location while still allowing sufficient room for installation, inspection and maintenance.
Installation and maintenance
Accessibility is an important consideration.
Equipment should be arranged so that it can be installed, tested and maintained safely and efficiently.
For larger installations, this can influence the design of equipment racks, cabinets and buildings.
Standard or bespoke requirements
Some projects can use established equipment designs, while others have specific requirements that call for a bespoke solution.
Bespoke design can be particularly relevant where equipment needs to fit an existing installation, accommodate unusual dimensions or integrate with a particular signalling arrangement.
Network Rail and approved signalling equipment
Railway signalling is a safety-critical environment, so equipment used on rail projects may need to meet specific technical and approval requirements.
However, approval status is product-specific.
Not every item of equipment used within a signalling installation will necessarily have the same approval or certification requirements.
For this reason, project teams should check the requirements applicable to the specific product, application and infrastructure owner.
RSP supplies a range of railway signalling products, including products with relevant Network Rail approvals and PADS approvals where applicable.
Rail signalling equipment from RSP
RSP manufactures and supplies a range of railway signalling equipment and supporting infrastructure for UK rail projects.
Our signalling range includes:
Trackside Connection Boxes
Signalling Location Cases
Signalling Equipment Racks
Relocatable Equipment Buildings
Functional Supply Points
Signal Aspect Flashing Relays
Plug Couplers
Component Boards
Magshields and other signalling components
RSP can also support projects requiring bespoke equipment and enclosures, with design and manufacturing capabilities developed around the requirements of the railway industry.
Whether the requirement is for a standard signalling component or a larger bespoke equipment solution, the correct specification starts with understanding the application, installation environment and requirements of the wider signalling system.
Explore RSP’s Rail Signalling Products
Frequently asked questions
What is railway signalling equipment?
Railway signalling equipment is the collection of systems, components and supporting infrastructure used to detect trains, control train movements and support the safe operation of the railway.
What equipment is used in railway signalling?
Railway signalling can involve train detection systems, interlocking equipment, signalling control equipment, location cases, trackside connection boxes, equipment racks, REBs, electrical connections, power supplies and specialist signalling components.
What is a railway signalling location case?
A signalling location case is a protective trackside enclosure used to house electrical and signalling equipment. It provides protection from the external environment while allowing the equipment inside to be accessed for installation and maintenance.
What is a Trackside Connection Box?
A Trackside Connection Box, or Dis Box, provides a protected enclosure for electrical connections associated with signalling and other trackside equipment.
What is an REB in railway signalling?
An REB, or Relocatable Equipment Building, is a prefabricated building used to house railway signalling, power, communications and associated equipment. It can be prepared away from the railway and transported to site for installation.
What is the difference between an axle counter and a track circuit?
Both can be used to detect whether a section of railway is occupied by a train, but they use different detection methods. Track circuits use an electrical circuit involving the rails, while axle counters detect and count train axles entering and leaving a defined section.
What is a signalling equipment rack?
A signalling equipment rack is a framework designed to mount and organise signalling equipment. Racks can be configured for different equipment types and applications, including relay and computer-based signalling systems.
Why does railway signalling equipment need protective enclosures?
Much signalling equipment is installed in exposed railway environments. Protective enclosures help shield electrical and signalling equipment from environmental conditions while providing suitable access for installation, testing and maintenance.
Summary
Rail signalling equipment is much more than the signals visible from the train driver’s cab.
Behind every signalling system is a network of detection equipment, interlocking and control systems, electrical connections, power supplies, equipment racks and protective enclosures.
From a small signalling component or Trackside Connection Box to a complete Relocatable Equipment Building, each element has a specific role within the wider railway infrastructure.
Understanding how these different elements fit together is an important starting point when specifying, designing or upgrading railway signalling equipment.