THE SIGNAL BOX

SIGNALS

SEMAPHORE SIGNALS

1. The basics

The principles of semaphore signalling as can be seen around the United Kingdom today go back to the 1850s but at that time there was no standardisation amongst signals for each railway company had its own ideas. It wasn't until the 1920s that national policies were applied, and the formation of the "big four" railway companies in 1923 is a convenient place to regard as the point at which the signals in use today became universally adopted. Of course, older signals were not wiped out overnight and many survived (perhaps in modified or repainted form) until recent years and a few can still be found around the railway system.

The earliest semaphore signals were known as lower quadrant signals, because the arm was lowered from horizontal to an inclined position when cleared. The first type lowered the arm to a vertical position, concealed inside the signal post, but this was abandoned in early years as the lack of a visible signal isn't the best way to indicate "clear" - a problem that can be illustrated by the behaviour of motorists when they find traffic lights unlit.

The other three members of the "big four" were quick to adopt upper quadrant signals, so that gravity could be used to return signals to danger. This kind of signal is now almost universal in semaphore areas across Network Rail outside the Great Western Zone.

Lower quadrant signal Somersault signal Upper quadrant signal
Lower quadrant
signal
Somersault
signal
Upper quadrant
signal

Colour Light signalling is now the accepted standard on Britain's railways and newly erected semaphore signals are now relatively rare. Sometimes colour light signals are directly substituted for (and often mixed with) semaphore signals and the equivalent indications are also shown on these pages. Although the indications are similar, this use of colour light signalling is quite different to true Multiple-Aspect Signalling which will be dealt with separately.

All signals are defined as on when showing a danger (horizontal) indication, and off when showing a proceed (angled at 35 to 85 degrees from the horizontal) indication. Signal posts may be of wood (painted white or creosoted), steel (usually painted white or silver) or concrete. Signal arms are painted wood or steel, or made of enamelled steel.

Signals are most commonly found on the left-hand side of the line they apply to, although there are exceptions.