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Section 2: Main Signals

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From 1892, the Board of Trade required that, in new works, only red or green lights be used in signals. This requirement was not mandatory on completely new lines, if they were to be used by trains belonging to any railway having a different system of lights. At a meeting of the Railway Clearing House on 27 July 1893, it was recommended that signals be altered to show only red or green lights.

The straight white stripe used on distant signal arms began to give way to a white chevron, which matched the shape of the fishtail notch [2.60 & 2.61]. This style of signal arm first appeared on the Great Western Railway.

[2.60] Semaphore Distant Signal ('on').
Area: Various   Usage: High   Status: Historical
[2.61] Semaphore Distant Signal ('off').
Area: Various   Usage: High   Status: Historical

While the adoption of the fishtailed arm in distant signals helped drivers to identify them during daylight, this was of no assistance to them at night. Stop signals and distant signals both showed either just a red light when 'on' or a green light when 'off', despite the difference in meaning between the two types of signal. To address this anomaly, some companies began to fit Coligny-Welch signal lamps to their distant signals from 1898. These displayed a white chevron of light to the right of the coloured lens, its shape resembling the fishtail notch in the arm [2.62 - 2.65]. The companies that chose to use these lamps were the LB&SCR, the L&SWR, the SECR, and from 1906 the GER, in certain parts of the London area.

[2.62] Semaphore Distant Signal with Coligny-Welch Lamp ('on').
Area: Various   Usage: High   Status: Historical
[2.63] Semaphore Distant Signal with Coligny-Welch Lamp ('off').
Area: Various   Usage: High   Status: Historical
[2.64] Semaphore Distant Signal with Coligny-Welch Lamp ('on').
Area: Various   Usage: High   Status: Historical
[2.65] Semaphore Distant Signal with Coligny-Welch Lamp ('off').
Area: Various   Usage: High   Status: Historical

'Enclosed semaphore' or 'banner' signals were used in a few places where clearances were restricted, e.g. at London Victoria (LB&SCR) in 1906/1907. This form of signal comprised a centrally pivoted, electrically operated arm inside a circular drum. When the arm was horizontal [2.66], the signal indicated 'stop', and when inclined at 45° [2.67], it indicated 'clear'. If acting as a distant signal, a fishtail notch was cut into the left-hand end of the arm [2.68 & 2.69]. Of note was the fact that these signals were illuminated during darkness and so gave the same indications by day or night.

[2.66] Banner Stop Signal ('on').
Area: Various   Usage: Medium   Status: Historical
[2.67] Banner Stop Signal ('off').
Area: Various   Usage: Medium   Status: Historical
[2.68] Banner Distant Signal ('on').
Area: Various   Usage: Low   Status: Historical
[2.69] Banner Distant Signal ('off').
Area: Various   Usage: Low   Status: Historical

Banner type main signals on the Great Western Railway had a red arm on a black background [2.70 & 2.71].

[2.70] Banner Stop Signal ('on').
Area: GWR   Usage: Low   Status: Historical
[2.71] Banner Stop Signal ('off').
Area: GWR   Usage: Low   Status: Historical

During 1912, the Swedish company AGA was promoting its flashing acetylene gas signal lamps to various British railway companies. It was thought that they could be used on distant signals to distinguish them from stop signals at night. The GWR experimentally fitted one of its distant signals with a flashing AGA lamp in 1913 but this did not find favour. The lamps proved more of a success on the Furness Railway, where they were adopted as standard on distant signals. When the distant signal arm was in the 'off' position, the lamp displayed a flashing white light [2.72].

[2.72] Semaphore Distant Signal with Flashing Lamp ('off').
Area: Fur.R   Usage: Unknown   Status: Historical

The widespread use of three-position semaphore signals in North America was generating some interest among the British companies. As described at the beginning of this section, three-position semaphore signals working in the lower quadrant had formerly been used in Britain in conjunction with the time interval system. The new three-position semaphores, however, were motor-operated and worked in the upper quadrant to differentiate them from the ordinary two-position semaphores. The arm raised through 45° from horizontal indicated 'caution' [2.73], and through 90° meant 'clear' [2.74]. The 'danger' indication was given when the arm was in the horizontal position, the same as a two-position lower quadrant signal (see [2.9]). These three-position semaphore signals introduced the use of a yellow light for 'caution' into British signalling practice for the first time. The first company to have one of these signals installed was the Great Western Railway in 1914, at London Paddington.

[2.73] Three-position Semaphore Signal showing 'Caution'.
Area: Various   Usage: Medium   Status: Historical
[2.74] Three-position Semaphore Signal showing 'Clear'.
Area: Various   Usage: Medium   Status: Historical

Although contrary to the Board of Trade's requirement of 1892, the advantage of having a yellow light as an unambiguous 'caution' indication was obvious. If applied to two-position semaphore signals, drivers would be able to distinguish, during darkness, a distant signal in the 'on' position from a stop signal. In 1916, the Great Central Railway began replacing the red lenses in its two-position distant signals with yellow lenses [2.75].

[2.75] Semaphore Distant Signal ('on').
Area: GCR   Usage: Unknown   Status: Historical

When the red lens in a distant signal is altered to yellow, it is logical that the same change of colour be made to the arm. Around 1918, the Great Central Railway fitted yellow arms to some distant signals in the London area [2.76 & 2.77].

[2.76] Semaphore Distant Signal with Yellow Arm ('on').
Area: GCR (subsequently All Areas)   Usage: High   Status: Current
[2.77] Semaphore Distant Signal with Yellow Arm ('off').
Area: GCR (subsequently All Areas)   Usage: High   Status: Obsolescent