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.
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. The approach to the siding connection and
the 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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In this diagram, 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.
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The unit has now completed its move to the platform and is
awaiting the train in service to approach and couple.
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Unit 2, the service train, has drawn up to the warning signal
and stopped. The warning signal clears now that the train has stopped.
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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.
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Unit 2, the service train, has now drawn up to the unit in
the platform and is ready to couple.
An unusual arrangement existed at Epping (Central Line) until
the area was resignalled in 1996. The exit from the east siding was protected by a
shunt signal and al calling-on signal on the same post, LW 25 and LW 26. There seems
to be no logic to this since the driver of a unit coupling to one in the platform would
proceed at caution expecting to see something ahead anyway. See the Epping - Ongar diagram here.
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Calling-on signals as originally installed in 1932 at Arnos
Grove EB home signal. At this time, junction signals were still separated (or split)
so that there was one for each route. Here, three routes are available into three
platforms. After W.W.II, junctions were indicated by route lights or "Harbour
Lights" as they are known.
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Calling-on signal at Parsons Green (District) EB home signal,
still in existence some 30 years after uncoupling was abandoned on the District.
Photo by District Dave.
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