Radio Electronic Token Block – What is RETB?

RETB is a cost-effective in-cab digital system for signalling rural, single track rail networks

RETB (Radio Electronic Token Block) is a system of railway block signalling designed for single track rail routes with light to medium traffic density. It is a development of the physical token system, but uses a radio network to issue an electronic token directly to the driver.

The track route is typically divided into block sections with a passing loop at each end:

How RETB Works

When a train is required to move into a new section, the signaller issues a movement authority permission token for that section to the train. In order to receive the token, the driver activates the ‘receive’ function on the in-cab equipment. This starts a radio transmission that is coded to match the identification number of that train. Together these safeguards guarantee that the train receives the correct token.

The token gives the driver permission to proceed into the track block, deactivating the automatic train protection for that section. A SIL level 4 interlocking system controls the issue of all movement tokens, protecting the single track sections.

The driver receives a movement token displayed on the in-cab equipment.

Close-up of the section token on display.

Signalling Centre – Centralised control over long routes

The RETB Signalling Desk provides simple, centralised control of the entire route. A single signaller can control all train movements on many hundreds of kilometres of route. As route utilisation and capacity increase the system can scale by splitting into areas on multiple desks to share signaller work load.

RETB has remote condition monitoring built-in. Signallers and remote users can get live data from base stations and mobile radios, along with historical trend data on radio network performance. This information is invaluable in helping support technicians diagnose issues early.

RETB’s innovative radio network architecture boosts safety and efficiency

The Comms Design RETB system comes with its own radio network. The radio base stations form a self-contained chain of coverage cells with a ‘virtual backhaul’ between them with no need for other supporting radio links, e.g. microwave. Radio calls from trains are transmitted from base station to base station and back to the signalling centre. Train radios automatically tune to the strongest radio channel as they move along the route. All users hear all calls, enhancing situational awareness and safety. The modular radio system can be installed onto existing radio masts, further decreasing the cost of entry for our digital in-cab signalling system.

Tested & Certified

RETB equipment has undergone rigorous EMC and environmental testing to ensure its reliability under all conditions. It is product approved by Network Rail for use on the UK rail network.

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Benefits of RETB:

Very low track-side infrastructure requirements

A single signalling desk can control the entire route

Flexible on-train equipment installation. Already in use on 23 loco & rolling stock types.

SIL Level 4 Solid State Interlocking maintains safe token issue

Long-range VHF radio means only a few base-stations required to cover long routes

Modular base-station equipment improves resilience and aids maintenance

Remote monitoring of equipment to check performance and ease fault finding

Fully supported with test equipment for line-side crews and depot teams.

Comprehensive Training courses and materials available for maintainer proficiency