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Section 6: Junction Signals and Route Indicators

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As an alternative to the provision of separate signals as so far described, a route indicator may be used in conjunction with a single signal. This is particularly advantageous where there is a great number of routes, such as on the approach to a large station. Route indicators were first used at London Bridge, in 1881.

The most basic type of route indicator displays a different character or characters depending upon the route that is set. When the signal is at 'danger' no route indication is shown and the indicator is blank, except that an early design of route indicator displayed a white triangle of lights when not displaying a character [6.13]. When the signal was cleared, a route indication was exhibited [6.14].

[6.13] Route Indicator (signal 'on').	[6.14] Route Indicator (signal 'off', e.g. "4" displayed).

The actual characters displayed by route indicators vary from place to place and drivers must learn their applications in each individual case. A number is commonly displayed to indicate a platform road [6.14]. The letter "X" often refers to a wrong direction move, e.g. towards a Limit of Shunt indicator (see Section 5). Route indicators that display characters are now known generically as 'alphanumeric' route indicators. They have existed in a variety of forms including mechanical type [6.15], stencil type [6.16], projector type [6.17] and 'theatre' or 'multi-lamp' type [6.18]. Modern alphanumeric route indicators display similar indications using fibre-optic or LED technology. There are two sizes, known as 'standard' and 'miniature'.

[6.15] Alphanumeric Route Indicator - Mechanical Type.	[6.16] Alphanumeric Route Indicator - Stencil Type.


[6.17] Alphanumeric Route Indicator - Projector Type (e.g. "5" displayed, meaning 'Platform 5').	[6.18] Alphanumeric Route Indicator - 'Theatre' or 'Multi-Lamp' Type.

Alphanumeric route indicators are not suitable for high speed running. An alphanumeric route indicator may be provided on a high speed line if no indication is displayed for the high speed route, an indication being displayed only for a low speed divergence.

An alphanumeric route indication could be exhibited inside a banner type shunting signal [6.19].

[6.19] Banner Type Shunting Signal ('off') with Route Indication (e.g. "4" displayed).

Directional shunting signals of the banner type were used in a few places, e.g. Glasgow St. Enoch (Glasgow & South Western Railway) in 1898. The banner in these signals could rotate either to the left [6.20] or right [6.21] when cleared, to indicate the direction of route.

[6.20] Directional Shunting Signal (left-hand route set).	[6.21] Directional Shunting Signal (right-hand route set).

The junction signalling practices applicable to semaphore signals were perpetuated in the earliest colour light signalling schemes. A colour light signal might be provided with an alphanumeric route indicator (see [6.17 & 6.18]), however this was generally confined to lower speed complex areas such as large stations, as recommended by the report of the IRSE's Three-Position Signalling Committee published in 1924. The alternative was to provide multiple signal heads, one for each route [6.22]. The heads were stepped in height according to speed, the same as in semaphore signalling practice.

[6.22] Colour Light Junction Signal (e.g. 'clear' aspect for straight route).

The report of the IRSE's Three-Position Signalling Committee had also recommended that a colour light signal in rear of a junction signal should show a double yellow aspect (see [2.95]) whenever a diverging route was set. This idea found favour on the LMS, particularly following a derailment at Great Bridgeford on 6 June 1932. However, the practice was discontinued following an accident at Bourne End on 30 September 1945.

Another recommendation from the same report had suggested that where both routes were of a similar speed, the distant signal should be fitted with an illuminated indicator capable of displaying either "L" or "R" for the left-hand or right-hand route, respectively. This idea was not put into practice.

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 [2.93]) 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 [6.23]. 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.

[6.23] Colour Light Splitting Distant Signal (e.g. junction signal ahead cleared for left-hand route) (LMS).

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