Distant signal

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Distant signal is a term used to denote a type of railway signal that repeats the indication of a following signal and warns a train of the need to stop at that following home signal. The term originated in British English and is used throughout the English-speaking world. In some regions, notably North America, the terms distant signal and approach signal are both in common usage.

1 Application
2 Shapes and colours
3 Combined stop and distant signal
4 Other countries
- 4.1 Germany
- 4.2 Norway
5 See also
6 References

[edit] Application

Because of the long distance required to bring a moving train to a stand, distant signals must be located in advance of corresponding stop signal at least the braking distance of the worst braked train to use the route. This is particularly important on high speed routes. At one time it was practice to take sighting distance into account when positioning distant signals. The distant signal could therefore be positioned at less than braking distance to the corresponding stop signal.

In British signalling practice, a distant signal may not be cleared unless all of the associated stop signals controlled by the signal box in question are clear.

[edit] Shapes and colours

British Semaphore Distant Signal

Distant signals vary around the world, in shape, colour, illumination, and behaviour.

In the United Kingdom and in North America, distant signals consist of a semaphore arm. The end of the signal arm has a fishtail (notched "V") shape to distinguish it from a home signal, the latter having a flat-end arm. The distant signal arm is painted yellow with a black stripe also in the shape of the letter "V".

The application of both light and dark colours to the arm assists sighting regardless of the background. Where the background is particularly problematic to adequate sighting of the signal, an artificial background would be provided. Distant signals display a yellow light in the Caution position, and a green light in the Clear position.

[edit] Combined stop and distant signal

British Semaphore Home and Distant Signals on common post

Where signals are closely spaced, stop signals and distant signals can be mounted on the same post. The two signals are interlocked or "slotted" so that the distant signal can only clear if the stop signal is clear.

With mechanical signals, two lights are always shown.

With colour light signals, only one light is shown.

Combined stop and distant semaphore signals in North America behaved in a similar fashion, but this type of signal system is nearly extinct, with nearly all the remaining instances of combined stop and distant semaphore signals having been replaced by three-aspect colour light within recent years.

[edit] Other countries

[edit] Germany

In German, the term Vorsignal ("pre-signal") is the equivalent of the English term "distant signal". Indications for light signals are:

home signal showing Stop: distant shows two diagonal yellow lights.
home signal showing clear: distant shows two diagonal green lights.
home signal showing clear for reduced-speed route: distant shows diagonal yellow and green lights.

See also: German railway signalling