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Section 7: Co-acting Signals and Repeater Signals

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Where the sighting of a signal is adversely affected by curvature or an intervening overbridge or station canopy, etc., an extra signal may be installed to give drivers of approaching trains an earlier view of the indication shown. A driver who was expecting to find the signal at 'danger' but receives early information that the signal has cleared can accelerate sooner, so benefitting train running performance. Duplicate signals installed at the same longitudinal position are termed 'co-acting' signals, whereas an additional signal provided at a different longitudinal position from the signal it repeats is known as a 'repeater' signal.


Where co-acting semaphore signals were provided, the duplicate arms were usually mounted at different heights on the same post [7.1]. In some examples, only the lower arms had lamps and, in some cases, not every arm was duplicated [7.2]. Exceptionally, the duplicate signals were positioned on the opposite side of the line [7.3] or the arms may be arranged differently [7.4].

[7.1] Co-acting Semaphore Signals. * Click Here for Photo
Area: All Areas   Usage: High   Status: Current
[7.2] Co-acting Semaphore Signals. *
Area: All Areas   Usage: Medium   Status: Historical
[7.3] Co-acting Semaphore Signals. *
Area: All Areas   Usage: Medium   Status: Current
[7.4] Co-acting Semaphore Signals. *
Area: All Areas   Usage: Medium   Status: Historical
Note: The above illustrations serve only to show the positions of the signal arms. For full details of their appearance, refer to Section 2.

The famous 'bedstead' signal gantry erected on the London & North Western Railway at Rugby in 1895 represented the ultimate in co-acting signals, with all twenty-two arms being duplicated at different heights.

Repeater signals originally took the form of specially distinguished semaphore signals [7.5 - 7.10] that worked in conjunction with the signal ahead to which they referred. A train does not require to stop at a repeater signal in the 'on' position but may pass it and draw up to the main signal.

[7.5] Semaphore Repeater Signal ('on').
Area: Unknown   Usage: Unknown   Status: Historical
[7.6] Semaphore Repeater Signal ('off').
Area: Unknown   Usage: Unknown   Status: Historical
[7.7] Semaphore Repeater Signal ('on').
Area: LB&SCR   Usage: Unknown   Status: Historical
[7.8] Semaphore Repeater Signal ('off').
Area: LB&SCR   Usage: Unknown   Status: Historical
[7.9] Semaphore Repeater Signal ('on').
Area: L&SWR   Usage: Unknown   Status: Historical
[7.10] Semaphore Repeater Signal ('off').
Area: L&SWR   Usage: Unknown   Status: Historical

At Aberdare (High Level) on the Great Western Railway, there was a rare example of a repeater for a backing signal. The arm of the repeater was similar in appearance to that of an ordinary backing signal (see [3.21 & 3.22]) except that it had a fishtail in the end [7.11 & 7.12].

[7.11] Distant Backing Signal ('on').
Area: Aberdare, GWR   Usage: Low   Status: Historical
[7.12] Distant Backing Signal ('off').
Area: Aberdare, GWR   Usage: Low   Status: Historical

Banner type repeater signals began to appear following the patenting of an improved design of banner signal by the W.R. Sykes Interlocking Signal Co. in 1909. Since banner signals with red arms were already being used as main signals (see [2.66 - 2.69]) and shunting signals (see [3.31 & 3.32]), it was necessary to specially distinguish those that were to function as repeaters. On the London Brighton & South Coast Railway, this was achieved by endorsing the face of the signal with a letter "R" [7.13 & 7.14]. If repeating a distant signal, a fishtail notch was cut into the left-hand end of the arm [7.15 & 7.16].

[7.13] Banner Repeater with Red Arm ('on').
Area: LB&SCR   Usage: Unknown   Status: Historical
[7.14] Banner Repeater with Red Arm ('off').
Area: LB&SCR   Usage: Unknown   Status: Historical
[7.15] Fishtailed Banner Repeater with Red Arm ('on').
Area: LB&SCR   Usage: Unknown   Status: Historical
[7.16] Fishtailed Banner Repeater with Red Arm ('off').
Area: LB&SCR   Usage: Unknown   Status: Historical

In 1916, the London & South Western Railway installed colour light repeaters on the platform roads at Waterloo.

At a few locations, electric light fog repeaters were provided. The lights in these signals were normally extinguished, being exhibited only when fog or falling snow caused poor visibility conditions. The fog repeaters installed on the Ealing & Shepherd's Bush Railway (GWR) in 1920 displayed an orange aspect [7.17] if the signal being repeated was at 'danger', or a green aspect [7.18] if the signal was at 'caution' or 'clear'. The words "fog repeater" were written on the face of the repeater, as was the number of the signal to which it referred.

[7.17] Fog Repeater ('on') (e.g. refers to signal number S81).
Area: Ealing & Shepherd's Bush Railway   Usage: Medium   Status: Historical
[7.18] Fog Repeater ('off') (e.g. refers to signal number S81).
Area: Ealing & Shepherd's Bush Railway   Usage: Medium   Status: Historical

By 1922, the Great Northern Railway was using semaphore repeater signals comprising a yellow 'somersault' type arm endorsed with a letter "R" [7.19 & 7.20].

[7.19] Semaphore Repeater Signal ('on').
Area: GNR   Usage: Unknown   Status: Historical
[7.20] Semaphore Repeater Signal ('off').
Area: GNR   Usage: Unknown   Status: Historical