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Section 6: Junction Signals and Route Indicators

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Practice regarding the colour light form of splitting distant signals varied between the different companies. LMS practice was to show only a single yellow aspect (see [2.97]) when the junction signal was at 'danger' (the junction signal may be another colour light or a semaphore). When the junction signal cleared, the splitting distant in rear could display a double yellow or green aspect alongside a single yellow aspect in a separate head [6.25]. Relative to this single yellow aspect, the other (less restrictive) aspect is positioned to the left or right, indicating which direction the train will take at the junction ahead. This form of signal was used only at junctions where both routes were of comparatively equal speeds.

[6.25] Colour Light Splitting Distant Signal (e.g. junction signal ahead cleared for left-hand route).
Area: LMS   Usage: Medium   Status: Historical

The colour light signalling installed by the LMS at Mirfield in 1932 (see [2.114 & 2.115]) was an experiment in 'speed signalling'. In that respect it was unique, since British practice has otherwise always employed 'route signalling'. A.F. Bound, Signal Engineer of the LMS, was a great believer in the merits of speed signalling, in which the driver is advised at which speed the train may safely negotiate the route but is not explicitly informed of which route it will take.

A junction signal was provided where the speeds of the main and diverging lines differed by more than 20 m.p.h. When at 'danger', the junction signal displayed two red lights vertically, in addition to a marker light [6.26]. The marker light at a junction signal was always illuminated, except when a low speed shunting or subsidiary aspect was displayed. When a main high speed route was set, the upper red light was replaced by an appropriate main proceed aspect [6.27]. When a diverging line, medium speed route was set, the lower red light in the main signal head (i.e. not the marker light) would change to a main proceed aspect [6.28] (not including a yellow over green aspect).

[6.26] Speed Signalling Junction Signal displaying a 'stop' aspect.
Area: Mirfield, LMS   Usage: Medium   Status: Historical
[6.27] Speed Signalling Junction Signal cleared for main high speed route (e.g. 'pass second signal at restricted speed').
Area: Mirfield, LMS   Usage: Medium   Status: Historical
[6.28] Speed Signalling Junction Signal cleared for medium speed route (e.g. 'clear').
Area: Mirfield, LMS   Usage: Medium   Status: Historical

The Southern Railway did not usually provide route indications at shunting signals. An exception was sometimes made for a signal that read either onto a running line or into a short shunt spur, etc. In this situation, and where miniature colour light signals were the desired form of shunting signal, two signals could be placed side by side. The signal applicable to the shunt spur was the one placed on the corresponding side of the pair. When at 'danger', both signal heads showed a red aspect. When cleared for a route onto the running line, the appropriate head changed to a green 'proceed' aspect. When the other head was cleared for the shunt spur, a yellow light was displayed [6.29], indicating the greater degree of caution required.

[6.29] Directing Miniature Colour Light Shunting Signal, 'off' for route towards shunt spur (e.g. left-hand route).
Area: Southern Railway   Usage: Medium   Status: Historical

The GWR and the CLC commonly provided stencil type route indicators in association with their miniature colour light shunting signals; however, if only two route indications were required (i.e. left or right), then a special form of signal was used, which avoided the provision of a route indicator. When the signal was cleared, a green light was illuminated but the red light remained lit. The position of the green light in relation to the red light identified the direction of the route. When the left-hand route was cleared, the 'proceed' aspect was green over red [6.30]. A red over green aspect [6.31] was shown for the right-hand route. The 'off' aspects were therefore equivalent to the indications presented by a two-tier disc shunting signal during darkness.

[6.30] Miniature Colour Light Shunting Signal, 'off' for left-hand route.
Area: GWR / CLC   Usage: Medium   Status: Historical
[6.31] Miniature Colour Light Shunting Signal, 'off' for right-hand route.
Area: GWR / CLC   Usage: Medium   Status: Historical

In the GWR's 1933 resignalling at Cardiff, any shunting signals that were elevated were equipped with an unusual form of route indicator. These were known as 'pointer light' route indicators and were very similar to those designed by W.K. Wallace and put into service at the LMS Northern Counties Committee's terminus at York Road, Belfast, in 1926. The pointer light route indicators provided at Cardiff comprised pairs of small red and green lights, one pair for every possible route from the signal (up to a maximum of ten). These lights were all extinguished when the associated shunting signal displayed a 'stop' aspect. When the signal was cleared, all the red lights in the route indicator were illuminated, except for the one that corresponded in position to the route that was set. The green light in that position was illuminated instead [6.32].

[6.32] Pointer Light Route Indicator (e.g. second route from the left is set, out of a possible eight routes).
Area: Cardiff, GWR   Usage: Medium   Status: Historical

In some areas, forward-facing route indicators displayed the various indications in an amber or yellow colour [6.33] to prevent glare. Where rear-facing route indicators were provided, these displayed their indications in white. Around 1962 the practice was reversed, amber coloured indications being reserved for rear-facing indicators.

[6.33] Route Indicator displaying Amber Indication (e.g. Theatre Type).
Area: Various   Usage: High   Status: Historical

In 1933, the LNER undertook a trial of a new form of route indicator for use in conjunction with a colour light junction signal, as an alternative to providing separate signal heads (see [6.22]). The signal selected for this trial was U22C at Thirsk, a three-aspect searchlight signal with additional offset heads for the diverging routes to the left and right of the Up Main line. Invented by A.E. Tattersall and patented by him, the new indicator displayed a bar of light formed of neon tubes, fixed at an appropriate angle to indicate the direction of the route. When the signal was at 'danger', no route indication was shown. When the straight-ahead route was set, a vertical bar of deep orange light was illuminated [6.34]. When a diverging route was set, the bar of light was inclined at 45° to the left or right, as appropriate [6.35]. Although the principle of the junction indicator was met with approval, the deep orange hue of the neon tubes and the high voltage needed to illuminate them resulted in no more of this style being installed.

[6.34] Experimental Junction Indicator (e.g. straight route set; signal at 'clear').
Area: Thirsk, LNER   Usage: Low   Status: Historical
[6.35] Experimental Junction Indicator (e.g. left-hand diverging route set; signal at 'caution').
Area: Thirsk, LNER   Usage: Low   Status: Historical

LNER practice with regard to colour light splitting distant signals differed slightly from LMS practice (see [6.25]). One similarity was that when the junction signal was at 'danger', the splitting distant signal would display only one single yellow aspect when cleared. Another similarity was the two additional signal heads provided to indicate direction of divergence; however, in the LNER signals, both would illuminate together when the junction signal was cleared [6.36]. The head situated on the same side as the route to be taken would clear to green while the other showed yellow. If both routes were of a similar speed then the two lower lights were displayed at the same height [6.36]; otherwise, the lights were stepped according to the relative speed of each route [6.37].

[6.36] Colour Light Splitting Distant Signal (e.g. junction signal ahead cleared for right-hand route) (routes of similar speed).
Area: LNER   Usage: Medium   Status: Historical
[6.37] Colour Light Splitting Distant Signal (e.g. junction signal ahead cleared for (lower speed) right-hand route).
Area: LNER   Usage: Medium   Status: Historical