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Section 6; pages:
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5
Section 6: Junction Signals and Route Indicators
(Page 3 of 5)
The colour light signalling installed by the LMS at Mirfield in 1932 (see [2.107 - 2.110]) 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 he may safely travel, but is not informed of the actual route to be taken.
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 would be 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).
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[6.24] Speed signalling junction signal displaying a 'stop' aspect.
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[6.25] Speed signalling junction signal cleared for main high speed route (e.g. 'pass second signal at restricted speed').
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[6.26] Speed signalling junction signal cleared for medium speed route (e.g. 'clear').
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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 form of shunting signal being used, 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.
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[6.27] Directing miniature colour light shunting signal, 'off' for route towards shunt spur (e.g. left-hand route) (SR).
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The GWR and 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 provision of an alphanumeric route indicator. When the signal was cleared, a green light would be illuminated but the red light would remain lit. The position of the green light in relation to the red light determined 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 given by a two-tier disc shunting signal during darkness.
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[6.28] Miniature colour light shunting signal, 'off' for left-hand route.
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[6.29] Miniature colour light shunting signal, 'off' for right-hand route.
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In the GWR's 1933 resignalling at Cardiff, any shunting signals that were elevated used a different type 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 used 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. In that position, the green light would be illuminated instead [6.30].
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[6.30] Pointer Light Route Indicator (e.g. second route from the left is set, out of a possible eight routes).
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In 1933, the LNER trialled a new form of route indicator at Thirsk. This was 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 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 red 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]. The red light bars were formed from neon tubes. This type of junction indicator was invented and patented by A.E. Tattersall.
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[6.31] Experimental Junction Indicator (e.g. straight route set, signal at 'clear').
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[6.32] Experimental Junction Indicator (e.g. left-hand diverging route set, signal at 'caution').
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When position light shunting signals were first introduced (see [3.62 & 3.63]), it was customary for two signals of that type to be positioned one above the other for routeing purposes [6.33]. As per traditional practice, the top signal referred to the left-hand route. If more than two routes needed to be indicated, an alphanumeric route indicator would be provided in association with a single signal head. The practice of providing two position light signals together for routeing purposes was discontinued from c.1962.
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[6.33] Two-tier position light shunting signal (e.g. white light type, 'off' for right-hand route).
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