Home Page > Section 5

Section 5: Limit of Shunt Indicators

(Page 1 of 1)


A form of fixed indicator is usually provided to mark the limit of a signalled shunting movement, where no other suitably located signal exists. This typically applies where a shunting movement can be signalled along a unidirectional running line in the opposite direction to normal running movements. Often, an ordinary shunting signal (see Section 3) was provided and fixed permanently in the 'on' position; however, it was the practice of some railway companies to install a distinctive 'limit of shunt' (LOS) 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

The Ministry of Transport 'Requirements' of 1925 called for the provision of "an indication, visible by night and day" to limit wrong-direction shunting movements along running lines. 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 alternative wording "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 the clearing of a main signal (see Section 2) authorised a train to proceed past a 'limit of shunt' indicator and towards the next main signal ahead. At some locations where this applied, drivers were instructed to disregard the LOS under this circumstance. At certain other locations, the LOS concerned (sometimes called a 'secret LOS') was either worked to exhibit a 'proceed' indication (if mechanical) or extinguished (if illuminated).


A reflectorised design of LOS 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: Predominantly Scotland   Usage: Medium   Status: Obsolescent

In 1985, a new standard form of LOS 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 [3.87]), the position light type LOS permanently showed two red lights [5.7]. In mechanically signalled areas, a fixed mechanical disc signal (see [3.46]) became the standard form of LOS.

[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 [3.100]) displayed the same 'stop' indication as a modern LOS indicator (two red lights). Consequently, LOS indicators provided in new works are practically indistinguishable from worked shunting signals displaying an 'on' indication.