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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 suitably located signal exists. This typically applies where a shunting move can be signalled along a unidirectional 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 'on' position; however, some railway companies would install a distinctive 'limit of shunt' (L.O.S.) indicator for that purpose.



One company that used 'limit of shunt' indicators from an early date was the London Brighton & South Coast Railway. The indicator's appearance was similar to an ordinary working disc signal in the 'on' position (see [3.1]), with the addition of a letter "L" on the red target [5.1].

[5.1] Limit of Shunt Indicator.
Area: LB&SCR   Usage: Low   Status: Historical

By 1926, a standard form of 'limit of shunt' indicator had been introduced, bearing the words "limit of shunt" in red on a square white background [5.2]. These indicators were usually ground mounted and were either floodlit or illuminated internally. In some later examples, the background shape was altered to be circular [5.3]. Another variation had the words "limit of shunt" replaced with "shunt limit" [5.4 & 5.5].

[5.2] Illuminated Limit of Shunt Indicator. Click Here for Photo
Area: All Areas   Usage: High   Status: Obsolescent
[5.3] Illuminated Limit of Shunt Indicator.
Area: All Areas   Usage: High   Status: Obsolescent
[5.4] Illuminated Limit of Shunt Indicator. Click Here for Photo
Area: All Areas   Usage: High   Status: Obsolescent
[5.5] Illuminated Limit of Shunt Indicator.
Area: All Areas   Usage: High   Status: Obsolescent

There have been rare instances where a signalled move could be made past a 'limit of shunt' indicator. In these circumstances, the L.O.S. (sometimes called a 'secret L.O.S.') must be worked (if mechanical) or extinguished (if illuminated).


A reflectorised design of L.O.S. indicator, with the words "shunt limit" in black [5.6], began to appear in a few places from c.1984.

[5.6] Reflectorised Limit of Shunt Indicator. Click Here for Photo
Area: Predominately Scotland   Usage: Medium   Status: Obsolescent

In 1985, a new standard form of L.O.S. indicator was introduced, which was 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 [3.78]), the position light type L.O.S. permanently showed two red lights [5.7]. In mechanically signalled areas, a fixed mechanical disc signal (see [3.39]) became the standard form of L.O.S.

[5.7] Limit of Shunt Indicator. Click Here for Photo
Area: All Areas   Usage: High   Status: Current

A new design of position light shunting signal introduced in 1996 (see [3.87]) displayed the same 'stop' indication as a modern L.O.S. indicator (two red lights). Consequently, L.O.S. indicators provided in new works are practically indistinguishable from worked shunting signals displaying an 'on' indication.