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Section 6: Junction Signals and Route Indicators

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The colour light signalling installed by the LMS at Mirfield in 1932 (see [2.113 & 2.114]) 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 [6.24]. 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 [6.25]. 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 [6.26] (not including a yellow over green aspect).

[6.24] Speed Signalling Junction Signal displaying a 'stop' aspect.
Area: Mirfield, LMS   Usage: Medium   Status: Historical
[6.25] 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
[6.26] 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 would sometimes be 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 left-hand or right-hand signal, as appropriate. When at 'danger', both signal heads would show a red aspect. When cleared for a route onto the running line, the appropriate head would change to a green 'proceed' aspect. When the other head was cleared for the shunt spur, a yellow light was displayed [6.27], indicating the greater degree of caution required.

[6.27] 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 used miniature alphanumeric 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 an alphanumeric 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 [6.28]. A red over green aspect [6.29] 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.

[6.28] Miniature Colour Light Shunting Signal, 'off' for left-hand route.
Area: GWR / CLC   Usage: Medium   Status: Historical
[6.29] 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 [6.30].

[6.30] 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 1933, the LNER undertook a trial, at Thirsk, of a new form of route indicator for use in conjunction with a colour light junction signal, as an alternative to having multiple signal heads (see [6.22]). 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 [6.31]. When a diverging route was set, the bar of light was inclined at 45° to the left or right, as appropriate [6.32]. This type of junction indicator was invented by A.E. Tattersall and patented by him.

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

When position light shunting signals were first introduced (see [3.69 & 3.70]), it was customary for two signals of that type to be positioned one above the other where it was required to indicate which one of two routes was set [6.33]. In accordance with traditional practice, the top signal referred to the left-hand route. If more than two routes needed to be indicated, an alphanumeric route indicator was provided in association with a single signal head. The practice of providing two position light signals together for route indicating purposes was discontinued from c.1962.

[6.33] Two-Tier Position Light Shunting Signal (e.g. white light type; 'off' for right-hand route). Click Here for Photo
Area: All Areas   Usage: High   Status: Obsolescent

LNER practice with regard to colour light splitting distant signals differed slightly from LMS practice (see [6.23]). 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 [6.34]. 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 [6.34]; otherwise, the lights were stepped according to the relative speed of each route [6.35].

[6.34] 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
[6.35] Colour Light Splitting Distant Signal (e.g. junction signal ahead cleared for (lower speed) right-hand route).
Area: LNER   Usage: Medium   Status: Historical