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Calling On & Warning Signals

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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.

sig warning1.gif (6206 bytes)

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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sig warning2.gif (6496 bytes)

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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sig warning3.gif (6493 bytes)

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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sig warning4.gif (7095 bytes)

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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sig warning5.gif (7107 bytes)

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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sig warning6.gif (7229 bytes)

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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Arnos calling-on.jpg (22214 bytes)

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 sig.jpg (40034 bytes)

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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