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London Underground Signalling - Historical
This is a historical notebook about signalling on the Underground, containing a series of short articles on various types of signals used by the Underground. Some of the data is incomplete so Tubeprune will be delighted if any readers can help with filling in the gaps. Links to other pages on LU signalling are here:To LU Automatic Signalling To LU Semi Automatic Signalling To LU Signalling Types To Speed Control Signalling and Points To Victoria Line ATO page
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Contents
Calling-on and Warning Signals
Calling-on and Warning Signals
Calling-on and Warning signals were used where trains were coupled on running lines at stations. They are both derivatives of the shunt signal. A shunt signal is used to indicate to a driver that the train may proceed into a siding or depot or over a crossover where passengers will not be carried. The move is to be carried out at caution speed and the driver should watch out for a dead end, fixed red light or stop signal.
The Underground regularly coupled and uncoupled trains in service from the earliest days of electric operation. As these operations were usually carried out on running lines at stations meant that special signals were required to allow coupling operations. Originally, small semaphore signals were used. Later, colour light or disc signals were used. After the second world war, disc signals became the standard.
The following sequence of diagrams show the operation of the Warning and Calling-on signals during a coupling move at a station.
Fig 1: Typical layout of
warning and calling-on signals at station where coupling of service trains takes place.
A unit is stabled in
the siding ready for coupling to a train in service.
In Fig 1 above, the approach to a siding connection and a station platform is protected by a set of three home signals. The outer home is signal WF1 which provides protection a full speed braking distance from the platform. WF7 provides a second home to allow a train to run in quickly behind a departing train. A unit is stabled in the siding and this unit will be brought into the platform in preparation for the arrival of a service train comprising a second unit. The two units will be coupled in the platform.
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Fig 4: The route is now set up
and cleared for the unit in the siding to move to the platform. The shunt signal,
WF4, provides the exit
from the siding, WF7 is cleared to allow an unrestricted run into the platform. The
calling-on signal does not require to be cleared
because there is no train or unit occupying the platform. The shunt signal, WF4,
provides the exit from the siding, WF7 is cleared to
allow an unrestricted run into the platform. The calling-on signal does not require
to be cleared because there is no train or unit
occupying the platform.
Fig 5: The unit is now in the
platform awaiting the train in service to couple.
Fig 6: Unit 2, the service
train, has drawn up to the warning signal. This clears when the train has stopped.
Fig 7: Unit 2, the service
train, has now drawn up to the calling-on signal. Like the warning signal, this
clears when the train has
stopped.
Fig 8: Unit 2, the service
train, has now drawn up to the unit in the platform and is ready to couple.
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Updated 6 May 2002
