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Section 2: Main Signals

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The provision of yellow arms and lights on semaphore distant signals became a requirement of the Ministry of Transport in 1925. This rendered superfluous the Coligny-Welch lamps used on some railways (see [2.62 - 2.65]). The Locomotive Department of the Southern Railway objected to their removal, however, and in some cases they were retained for a period after yellow arms had been fitted [2.97 & 2.98]. There was even a suggestion that the colour of the chevron light should be altered from white to yellow when the new arms were fitted, but this was not done. The Southern Railway finally abolished its Coligny-Welch lamps in 1927.

[2.97] Semaphore Distant Signal with Yellow Arm and Coligny-Welch Lamp ('on').
Area: Southern Railway   Usage: Medium   Status: Historical
[2.98] Semaphore Distant Signal with Yellow Arm and Coligny-Welch Lamp ('off').
Area: Southern Railway   Usage: Medium   Status: Historical

The adoption of the upper quadrant semaphore signal (see [2.95 & 2.96]) was agreed to at a meeting of the Railway Clearing House on 20 July 1926. The 1928 issue of the MoT 'Requirements' no longer dictated that semaphore arms must operate in the lower quadrant, as the previous issue had done in 1925. The Great Western Railway (and subsequently the Western Region of B.R.) resisted any move towards adopting the upper quadrant signal and continued to install lower quadrant signals, almost exclusively.

The Southern Railway perpetuated its special use of main signals for entering the platform roads at terminus stations, which it inherited from the LB&SCR. Where a colour light signal was used in this situation, a yellow aspect (see [2.92]) meant that the platform road was already partially occupied, while a green aspect (see [2.93]) meant that the platform road was unoccupied (i.e. clear to the buffer stop). The LMS implemented similar arrangements at Glasgow St. Enoch in 1933.

In 1929, the arms of two banner distant signals between Higham and Strood (Southern Railway) were altered from red to yellow and their background colour was changed to black [2.99 & 2.100].

[2.99] Banner Distant Signal with Yellow Arm ('on').
Area: Southern Railway   Usage: Low   Status: Historical
[2.100] Banner Distant Signal with Yellow Arm ('off').
Area: Southern Railway   Usage: Low   Status: Historical

Apart from an early installation on the Engine and Carriage lines between London Paddington and Old Oak Common, the Great Western Railway chose not to install colour light signalling of the form that was becoming standard on the SR, the LMS and the LNER. Colour light signals installed on the GWR from 1931 displayed aspects that were the same as those shown by semaphore signals at night. Accordingly, a colour light stop signal could display either red for 'danger' or green for 'clear'. A colour light distant signal showed either yellow for 'caution' or green for 'clear'. The principles of semaphore signalling were perpetuated to the extent that a stop and distant signal could be mounted together on one post, with the stop signal head positioned above the distant. A 'danger' aspect was red over yellow [2.101], a 'caution' aspect was green over yellow [2.102], and a 'clear' aspect was green over green [2.103]. The last of these signals, at Bristol, were removed in the early 1970s.

[2.101] Red Aspect over Yellow Aspect.
Area: GWR   Usage: High   Status: Historical
[2.102] Green Aspect over Yellow Aspect.
Area: GWR   Usage: High   Status: Historical
[2.103] Green Aspect over Green Aspect.
Area: GWR   Usage: High   Status: Historical

A.F. Bound, in his new position as Signal Engineer of the LMS, devised a system of colour light signalling which was installed from June 1932 on the electrified lines between Camden and Watford Junction ('New' Line) and on the Local lines between Barking and Upminster. The main aspects included were the red aspect, yellow aspect, green aspect and a small number of double yellow aspects. Bound, who had visited the United States in 1931, incorporated an element of North American practice in the form of marker lights, despite the use of these having been recommended against in the report of the IRSE's Three-Position Signalling Committee in which he had served as Chairman. Since publication of the report in 1924, the rising use of colour light signals in nominally semaphore territory had convinced Bound of the need to distinguish signals within 'multiple-aspect colour light signal' territory by means of marker lights provided on the latter. Any signal that read towards a semaphore signal or a London Transport signal was not provided with a marker light. The marker light comprised a red light mounted lower down the post, below the main aspect. It was only illuminated while the main signal was displaying a 'danger' aspect [2.104], except that it was extinguished when a subsidiary aspect was displayed (see Section 4). Repeater signals on the Camden - Watford line had their marker lights offset to the left [2.105]. After stopping at one of these signals displaying a 'danger' aspect, the driver was permitted to proceed cautiously past the signal after waiting for one minute. The 'New' Line between Camden and Watford was resignalled with conventional colour light signals in 1988.

[2.104] Stop Signal with Marker Light.
Area: LMS   Usage: High   Status: Historical
[2.105] Repeater Signal with Marker Light.
Area: Watford New Line, LMS   Usage: Medium   Status: Historical

In July 1932, Bound's experimental colour light signalling scheme was commissioned in the Mirfield area on the LMS. One of the unique features of this scheme was the inclusion of five main signal aspects. In addition to the red aspect, yellow aspect, double yellow aspect and green aspect, the fifth aspect was yellow over green [2.106]. Inserted into the normal aspect sequence between the green aspect and the double yellow aspect where signals were closely spaced, the yellow over green aspect meant "attention - pass second signal at restricted speed". This unusual signalling installation survived until 1970, although the yellow over green aspects were abolished in 1959.

[2.106] Yellow over Green Aspect.
Area: Mirfield, LMS   Usage: Medium   Status: Historical

Red marker lights were also used in the Mirfield scheme on all colour light signals apart from those that read towards a semaphore signal. Where provided, the marker light was positioned on the post below the main aspect [2.104 & 2.107 - 2.109] and it remained illuminated except when the main signal was displaying a 'clear' aspect (see [2.93]) or when a shunting or subsidiary aspect was displayed. Bound's resignalling at Glasgow St. Enoch in May 1933 featured red marker lights similar to those at Mirfield, but this installation had no double yellow or yellow over green aspects.

[2.107] Single Yellow Aspect with Marker Light.
Area: LMS   Usage: Medium   Status: Historical
[2.108] Double Yellow Aspect with Marker Light.
Area: LMS   Usage: Medium   Status: Historical
[2.109] Yellow over Green Aspect with Marker Light.
Area: Mirfield, LMS   Usage: Medium   Status: Historical

In 1933, discussions commenced on the standardisation of colour light signals, at the instigation of the Ministry of Transport. This led the LMS to discontinue its practice of providing marker lights on signals for future installations.