British Railway Signalling

How it works

by Clive Feather

This is the start of a book on the topic of railway signalling. I'm writing it bit-by-bit, and most of the links are still missing - bold italics are used to show where I intend to put a link.

The basic purpose of railway signals is to give train drivers enough warning to stop. The big advantage of rail over other forms of surface transport is the low friction of steel wheel on steel rail. But this in turn makes it hard for the train to stop; a modern express train can require more than 2km to stop on the level and 3km to stop on a downhill slope.

Suppose there is an obstruction on the line ahead (whether it is another train, a conflicting route, or an injured child). The driver of an approaching train needs to be warned a long distance back. This distance can be split into three parts:

Diagram of distances

All signalling systems provide these three distances in one way or another, and the purpose of all signalling systems is to provide them.

The main railways in Great Britain are owned, and the signalling controlled, by Railtrack. Signalling on these railways has evolved over more than a hundred and fifty years, and so there is no one simple system. The following pages describe the significant features of Railtrack signalling:

As well as Railtrack there are a number of other railway systems in Great Britain. The interesting ones from the signalling aspect are:

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