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Section 4: Subsidiary Signals

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A 'shunt-ahead' signal may be provided at a main stop signal that controls the entrance to the section ahead. When cleared, it authorises a train to pass the main signal for shunting purposes only, so that it may then set back through some trailing points. There were various designs of shunt-ahead signal [4.26 - 4.31].

[4.26] Shunt-ahead Signal ('on').
Area: Cal.R / NBR   Usage: Unknown   Status: Historical
[4.27] Shunt-ahead Signal ('off').
Area: Cal.R / NBR   Usage: Unknown   Status: Historical
[4.28] Shunt-ahead Signal ('on').
Area: GWR   Usage: Unknown   Status: Historical
[4.29] Shunt-ahead Signal ('off').
Area: GWR   Usage: Unknown   Status: Historical
[4.30] Calling-on or Shunt-ahead Signal ('on').
Area: S&DJR   Usage: Unknown   Status: Historical
[4.31] Calling-on or Shunt-ahead Signal ('off').
Area: S&DJR   Usage: Unknown   Status: Historical

A 'warning' signal, when cleared, authorises the driver to proceed to the next stop signal. The driver must understand that the line is clear as far as the next stop signal only but might be obstructed immediately beyond it. The speed of the train must be regulated accordingly. Where provided, a warning signal was usually placed at a main stop signal that controlled the entrance to the section ahead.

Warning signals were uncommon at one time but the LB&SCR had some in the London District, working in conjunction with Sykes Lock and Block. These took the form of a rotating white disc or banner incorporating a 'bow-tie' arm in red [4.32 & 4.33].

[4.32] Warning Signal ('on').
Area: LB&SCR   Usage: Unknown   Status: Historical
[4.33] Warning Signal ('off').
Area: LB&SCR   Usage: Unknown   Status: Historical

The Great Central Railway also had a few warning signals, working in connection with Evans Lock and Block. These comprised a small centrally pivoted semaphore arm with a distinctive sloping end [4.34 & 4.35].

[4.34] Warning Signal ('on').
Area: GCR   Usage: Unknown   Status: Historical
[4.35] Warning Signal ('off').
Area: GCR   Usage: Unknown   Status: Historical

Where the Great Western Railway provided banner type main signals (see [2.72 & 2.73]) and a calling-on signal was required, it took the form of a miniature banner endorsed "CO" on the arm [4.36 & 4.37].

[4.36] Banner Type Calling-on Signal ('on').
Area: GWR   Usage: Low   Status: Historical
[4.37] Banner Type Calling-on Signal ('off').
Area: GWR   Usage: Low   Status: Historical

In 1920, the GWR's Ealing & Shepherd's Bush Railway was resignalled with three-position semaphore signals working in the upper quadrant (see Section 2). Where calling-on signals were required, they comprised two-position semaphore signals (also working in the upper quadrant) endorsed "CO" on the arm, with one letter on either side of the white stripe [4.38 & 4.39].

[4.38] Calling-on Signal ('on').
Area: Ealing & Shepherd's Bush Railway   Usage: Low   Status: Historical
[4.39] Calling-on Signal ('off').
Area: Ealing & Shepherd's Bush Railway   Usage: Low   Status: Historical

Where a main signal in the form of a large disc (see [2.93 & 2.94]) required an associated calling-on signal, the latter would be a normal-sized disc endorsed "CO" [4.40 & 4.41].

[4.40] Disc Type Calling-on Signal ('on'). Click Here for Photo
Area: GWR   Usage: Low   Status: Obsolescent
[4.41] Disc Type Calling-on Signal ('off').
Area: GWR   Usage: Low   Status: Obsolescent

The Ministry of Transport 'Requirements' of 1925 had stipulated that calling-on and shunt-ahead signals (warning signals were not mentioned) should display a white light in the 'on' position. It therefore followed that the colour of the signal arm should also be white. In 1926, a subsidiary signal comprising a small white arm with two horizontal red stripes [4.42] was installed on the LNER at Cambridge. To distinguish more clearly the functions of the various types of subsidiary signal, around 1925, distinguishing letters "C", "S" or "W" began to be exhibited alongside the lamp when the signal arm was 'off' [4.43 - 4.48]. The letter was hidden behind the arm when 'on'.

[4.42] Subsidiary Signal ('on').
Area: All Areas   Usage: High   Status: Current
[4.43] Lower Quadrant Calling-on Signal ('off').
Area: All Areas   Usage: High   Status: Obsolescent
[4.44] Upper Quadrant Calling-on Signal ('off').
Area: All Areas   Usage: High   Status: Current
[4.45] Lower Quadrant Shunt-ahead Signal ('off').
Area: All Areas   Usage: High   Status: Obsolescent
[4.46] Upper Quadrant Shunt-ahead Signal ('off').
Area: All Areas   Usage: High   Status: Current
[4.47] Lower Quadrant Warning Signal ('off').
Area: All Areas   Usage: High   Status: Obsolescent
[4.48] Upper Quadrant Warning Signal ('off').
Area: All Areas   Usage: High   Status: Obsolescent