How do railway and train signals work and how do trains know the track ahead is clear?

Bex and Dan discover more!

Since the earliest days of rail, trains have been controlled by their very own ‘highway code’ to keep them a safe distance apart.

Every railway line is divided up into sections called blocks where only one train at a time is allowed to be.

Signalling has kit attached to tracks to determine whether or not a train is in a section – this kit includes track circuits which send a small electrical current between the tracks and trains, and axle counters which count the wheels going in and out of a section.

If the numbers match, the section is clear for the next train.

Trackside signals control entry into and out of each block and also warn trains when the line ahead might be occupied and if they must reduce speed.

Just like on a road, there are also speed limit signs, reducing speeds in built up areas and where there are hazards. There’s lots of ways to make sure everyone stays safe, as Bex and Dan find out!

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In the earliest days of rail travel, policemen would stand along the track and use flags to tell train drivers if the track ahead was clear.

As they couldn’t communicate with neighbouring policemen, the only way to do this was to time each train as it came past and leave a set amount of time before letting the next one past.

As trains started to get faster and more frequent, things had to change.

Mechanical semaphore signals controlled by signalmen were introduced. The signalmen could now also communicate with each other using bells and lamps.

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From the 1960s, traffic light signals began to be used to control trains, with signals able to show cautionary yellow as well as stop and go, red and green.

As well as being easier to see, as they are controlled by relays and computers rather than mechanical metal rods, they are more reliable.

With modern technology advancing all the time, signalling has definitely come into the 21st Century!

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The railways use a train detection systems which can tell signallers exactly where every train is and how fast they are going.

There are also systems that can automatically stop trains if the driver doesn’t take the correct course of action or passes through a red signal.

All helping the railways to run smoothly – and safely!

Find out more about Britain’s railways!

Bex and Dan from Fun Kids learn all about the future of Britain’s railways, from signals to trains and tracks, in this new podcast series!

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Kids Guide to Trains: Britain's Digital Railways

Bex and Dan learn all about the future of Britain's railways, from signals to trains and tracks!


Explore all the free Fun Kids podcasts!

Download a series to listen to on your phone, tablet or in the car!


Britain’s Digital Railways, in association with the Royal Academy of Engineering

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