Section 2: Main Signals
(Page 1 of 7)
The first railway semaphore signal was erected in 1841 at New Cross Gate by Charles H. Gregory, Engineer of the London & Croydon Railway. During daylight hours, a semaphore signal conveys its indications by means of a pivoted 'arm'. The arm projects to the left of the post when viewed in the applicable direction of travel, and its angle determines the indication. The first semaphores were three-position signals, used in conjunction with the time interval system. The 'danger' indication was given by the arm being in the horizontal position [2.1]. A red light was shown at night. For the 'caution' indication, the arm was lowered through 45°, and a green light given at night [2.2]. In the 'clear' position, the arm dropped down vertically to be hidden behind the post, and a white light was shown at night [2.3].
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[2.1] Semaphore Signal showing 'Danger'.
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[2.2] Semaphore Signal showing 'Caution'.
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[2.3] Semaphore Signal showing 'Clear'.
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With the gradual introduction of the absolute block system, semaphore signals were only required to show two indications, 'danger' [2.1] or 'clear' [2.3]. However, at busy junctions etc. where more caution was required, signals continued to show either 'danger' [2.1] or 'caution' [2.2]. The GWR was the first to abolish the 'caution' indication, in 1873.
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Gradually, semaphore signals came to be worked to 45° for the 'clear' indication [2.4], rather than the former indication in which the arm had been hidden behind the post (see [2.3]).
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[2.4] Semaphore Signal showing 'Clear'.
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By the 1860s, semaphore signals were in widespread use, apart from on the Great Western Railway and the London & South Western Railway. The GWR began installing semaphores in 1865.
Initially, semaphore arms coloured all-red were used by the GWR, LNWR and Metropolitan Railway [2.5 & 2.6].
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[2.5] Semaphore Signal ('on').
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[2.6] Semaphore Signal ('off').
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Before long, it was realised that the signal arms could be made more conspicuous by the addition of a marking of contrasting colour. The Brighton Railway's signal arms were originally white with a red stripe (black stripe on rear) [2.7 & 2.8].
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[2.7] Brighton Railway Semaphore Signal ('on').
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[2.8] Brighton Railway Semaphore Signal ('off').
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Most other railways used red arms with a white stripe [2.9 & 2.10].
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[2.9] Semaphore Signal ('on').
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[2.10] Semaphore Signal ('off').
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Semaphore signals on the South Eastern Railway had a white spot instead of a stripe on the front of the arm [2.11 & 2.12].
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[2.11] South Eastern Railway Semaphore Signal ('on').
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[2.12] South Eastern Railway Semaphore Signal ('off').
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Midland Railway semaphores had spots on both sides of the arm [2.13 & 2.14].
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[2.13] Midland Railway Semaphore Signal ('on').
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[2.14] Midland Railway Semaphore Signal ('off').
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Cambrian Railways semaphores had arms with bulbous ends [2.15 & 2.16], a feature more commonly associated with the railways of continental Europe. One such signal, at Aberdovey, survived into the British Railways era.
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[2.15] Cambrian Railways Semaphore Signal ('on').
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[2.16] Cambrian Railways Semaphore Signal ('off').
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The London & North Western Railway had opened a third line for goods traffic as far as Bletchley, in stages from 1858. Semaphore signals had been installed on the new third line to avoid confusion with the existing signals on the passenger lines, which were of the old disc type (see [1.46 & 1.47]). To ensure that the goods line signals could be distinguished by drivers during darkness, a second lamp that permanently showed a green light was placed below the usual signal lamp. Thus a driver running at night would see a red light over a green light for the 'danger' indication [2.17] and a white light over green for 'clear' [2.18].
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[2.17] Semaphore Signal with additional Green Light ('on') (LNWR).
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[2.18] Semaphore Signal with additional Green Light ('off') (LNWR).
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By 1867, semaphore signals had been installed on the passenger lines referred to above. Rings were fitted to the arms of the goods line signals [2.19 & 2.20] so that they could continue to be distinguished during daylight. The LNWR was the first company to use ringed signal arms. They continued to fit rings in order to assist drivers in distinguishing signals where they were placed side by side on multiple track sections. Generally, the signal arms applying to goods lines or slow lines were fitted with rings, or where there were many lines, signals applying to alternate lines were fitted.
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[2.19] Ringed Semaphore Signal ('on') (LNWR).
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[2.20] Ringed Semaphore Signal ('off') (LNWR).
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