Section 7: Co-acting Signals and Repeater Signals

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Occasionally, co-acting colour light signals are provided. Examples of these were present in the first British mainline installation of colour light signals, at London Marylebone (LNER) in 1923. Usually, the duplicate signal is ground mounted (as at Marylebone) [7.21], and if advantageous to sighting, it may even be positioned on the opposite side of the track [7.22]. Exceptionally, a colour light signal head was provided to co-act with a semaphore signal [7.23].

[7.21] Co-acting Signals. Area: All Areas   Usage: Medium   Status: Current	[7.22] Co-acting Signals. Area: All Areas   Usage: Medium   Status: Current	[7.23] Co-acting Signals. Area: All Areas   Usage: Low   Status: Historical

Exceptionally, a co-acting colour light signal intended for short-range viewing may be provided in miniature form [7.24]. These miniature repeaters are of assistance to drivers of trains that require to stand so close to the signal that the main aspect is difficult to observe.

[7.24] Miniature Close-Up Signal. Area: All Areas   Usage: Low   Status: Current

In some instances, only the main aspects are duplicated on the co-acting signal, and not any associated shunting signals or route indicators [7.25].

[7.25] Co-acting Signals. Area: All Areas   Usage: Medium   Status: Current

For a few years, banner repeaters with yellow arms were provided in some places (without a distinguishing letter "R") [7.26 - 7.29]. The Southern Railway continued to use red banner repeaters endorsed with an "R" (see [7.13 - 7.16]).

[7.26] Banner Repeater with Yellow Arm ('on'). Area: Various   Usage: Unknown   Status: Historical	[7.27] Banner Repeater with Yellow Arm ('off'). Area: Various   Usage: Unknown   Status: Historical
[7.28] Fishtailed Banner Repeater with Yellow Arm ('on'). Area: Various   Usage: Unknown   Status: Historical	[7.29] Fishtailed Banner Repeater with Yellow Arm ('off'). Area: Various   Usage: Unknown   Status: Historical

The impending introduction of four-aspect colour light signalling had left signal engineers pondering the best form of repeater signal for use where sighting of a signal was restricted. The banner repeater, being a 'position' type signal, was suitable for a semaphore signal but was not considered appropriate for use with a colour light signal. Logically, a repeater of a colour light signal should itself be of the colour light type. If however the signal, and hence its repeater, were to be displaying a red aspect, drivers would have to pass the red light in the repeater to draw up to the main signal, which would be undesirable. To overcome this, the Southern Railway had proposed using what was termed an 'auxiliary signal' in preference to a repeater. An auxiliary signal comprised a small three-aspect head and a permanently illuminated white St. George's cross on a black background [7.30 - 7.33]. The auxiliary signal repeated the aspect that would be shown by the previous signal; thus, a single yellow light [7.30] was displayed when the signal ahead displayed red, or double yellow [7.31] when the signal displayed single yellow. The auxiliary signal would display a green light [7.32] when the main signal displayed either a double yellow or a green aspect. To prevent 'reading through' from the signal on approach, the auxiliary signal would display the white cross alone [7.33] while a train was standing at the main signal. Under normal circumstances, a train would never approach an auxiliary signal in this state. In the event, no auxiliary signals were needed in the earliest schemes, and it subsequently became normal practice to provide banner repeaters for colour light signals with restricted sighting.

[7.30] Auxiliary Signal showing 'Caution'. Area: Southern Railway   Usage: Nil   Status: Historical	[7.31] Auxiliary Signal showing 'Warning'. Area: Southern Railway   Usage: Nil   Status: Historical
[7.32] Auxiliary Signal showing 'Clear'. Area: Southern Railway   Usage: Nil   Status: Historical	[7.33] Auxiliary Signal (normal aspect). Area: Southern Railway   Usage: Nil   Status: Historical

In December 1926, fog repeaters were provided opposite two signals at Forest Hill (Southern Railway). These could display either a red or green aspect and were identified by a plate bearing the letter "F" [7.34 & 7.35].

[7.34] Fog Repeater ('on'). Area: Forest Hill, Southern Railway   Usage: Low   Status: Historical	[7.35] Fog Repeater ('off'). Area: Forest Hill, Southern Railway   Usage: Low   Status: Historical

Electric light repeater signals were occasionally provided, particularly for use inside tunnels where it was not practicable to install a banner repeater. A yellow aspect [7.36] was displayed when the signal ahead was 'on', or a green aspect [7.37] when the signal ahead was 'off'.

[7.36] Electric Light Repeater Signal ('on'). Area: All Areas   Usage: Medium   Status: Obsolescent	[7.37] Electric Light Repeater Signal ('off'). Area: All Areas   Usage: Medium   Status: Obsolescent