THE SIGNAL BOX

BLOCK SYSTEM

BLOCK SYSTEM

4. Working at junctions

On this page:
[ Clearing points | Setting for alternative route | Trains at a stand | Facing point locks | Outer home signals | Indecision and errors ]


While Bert was away in Margate at the weekend, the engineers have been in and laid a whole new branch line and have installed new points and signals. Bert needs to study his rules a bit deeper to see how to handle trains safely. He also has a new colleague to work with - Doris, who works in Box D on the branch line.

New "improved" layout at Signal Box "B"

Clearing Points

The working of junctions is really quite simple, although it doesn't always seem so when written down. Basically, Bert at Box B must not use the same piece of railway as the clearing point for more than one train.

So, if Bert has accepted a train from Doris at Box D, he cannot accept a train from Charlie at Box C. Likewise, Bert cannot accept a train from Doris if he has accepted a train from Charlie. Additionally, if Bert has accepted a train from Charlie, he cannot run a train from Box A towards the Branch.

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Setting for an alternative route

It is permissible to use an alternative clearing point. If Bert has accepted a train from Charlie at Box C, he is permitted to accept a train from Arthur at Box A for the branch line provided he has his points safely set towards Box C, and the clearing point in that direction is not fouled. After the train from Box C has either passed, or been brought to a stand at the Down Main Home, Bert can change the points to the correct route for the train.

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Trains at a stand

If a train has been brought to a stand at a home signal, the clearing point is no longer required. So, for instance, if a train has been accepted by Bert from Doris, he can accept a train from Charlie after the train from Doris has come to a stand at his home signal.

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Facing Point Locks

Where it is stated to be necessary for points to be correctly set before accepting trains, this includes locking them with the Facing Point Lock, if provided.

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Outer Home Signals

If the block section between Box B and Box D is quite long, disruption to train running on the main line could well be caused if Bert had to wait a long time from accepting a train to when it reached him. A common method of overcoming this is to provide an additional (or Outer) Home signal a quarter of a mile in rear of the existing home signal. This allows trains to be freely accepted on the line concerned without the restrictions described above.

Another workaround is to use the Warning Arrangement - this is discussed in Chapter 5.

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Indecision and errors

Another factor of junction working is found in the Rule Book, under Rule 70(a). Should a signalman give precedence to the wrong train at a junction, he must not just put the incorrect signals to "on" and clear the other ones. There is a risk that the train for which the signals have been wrongly cleared may not stop, as the driver may have already seen the distant in the off position. Therefore, all signals must be placed or maintained at danger until the wrongly signalled train has come to a stand. Only then may the signals be cleared for the other train.