Section 5: Limit of Shunt Indicators
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It is necessary to provide some form of fixed indicator to mark the limit of a signalled shunting movement, where no other signal exists that could serve the purpose. This typically applies where a shunting move can be signalled along a running line in the opposite direction to normal running moves. Often, an ordinary shunting signal (see Section 3) would be provided and fixed permanently in the 'danger' position, however some railway companies would install a distinctive Limit of Shunt (L.O.S.) indicator for that purpose [5.1 & 5.2].
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[5.1] Limit of Shunt Indicator (LB&SCR).
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[5.2] Limit of Shunt Indicator (NER).
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By 1926, the Great Western Railway had introduced a standard form of Limit of Shunt indicator bearing the words "Limit of Shunt" in red on a square white background [5.3]. British Rail adopted a similar style of indicator as standard. In some cases, the words "Limit of Shunt" were replaced with "Shunt Limit" and the background shape could be either square or circular [5.4 & 5.5]. These indicators are usually ground mounted and are either floodlit or illuminated internally.
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[5.3] Limit of Shunt Indicator (GWR).
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[5.4] Illuminated Limit of Shunt Indicator (BR).
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[5.5] Illuminated Limit of Shunt Indicator (BR).
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There have been a few rare cases where a signalled move can be made past a L.O.S. indicator. In these circumstances, the L.O.S. (sometimes called a 'secret L.O.S.') must be worked (if mechanical) or extinguished (if illuminated).
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A reflectorised design of L.O.S. indicator, with the words "Shunt Limit" in black [5.6], began to appear in a few places on the Scottish Region from c.1984.
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[5.6] Reflectorised Limit of Shunt Indicator (Scottish Region).
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In 1986, a new standard form of L.O.S. indicator was introduced, it being a derivative of the position light shunting signal. Whereas the ordinary position light shunting signal then in widespread use displayed one red and one white light horizontally as the 'stop' aspect (see [3.74]), the position light type L.O.S. permanently showed two red lights [5.7]. In mechanically signalled areas, a fixed mechanical disc signal (see [3.37]) became the standard form of L.O.S.
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[5.7] Limit of Shunt Indicator.
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A new design of position light shunting signal introduced in 1996 (see [3.83]) displayed the same 'stop' indication as a modern L.O.S. indicator (two red lights). Thus, L.O.S. indicators provided in new works have ceased to be distinguishable from worked shunting signals.
