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7.2 Train on Line
  
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Railway
Sri Lanka

As soon as the train passes the controlled signal at station A, the signal switches to 'danger'. Note that the "green" current is short circuited by the train axle and does not reach signal A.

Sooner or later the the controlled (home) signal at station B will be set to 'proceed' by the controller. As a result signal 3 switches to 'proceed' as well.

When the train leaves the first block, the the signal 1 switches to 'danger' since the "green" current is now cut off by the train. This signal post sends a "yellow" current backward. Since the signal A is a controlled signal it ignores the "yellow" current and remains 'danger'.

As the train enters block 3, the "yellow" current set the signal 1 to 'caution'.  "Green" current is sent to the previous signal. Now a new train can be dispatched on the line from A to B and ABS ensures at least on block space between the two trains.

The train proceeds and the "green" current switches the signal 1 to 'proceed'. Now you can deduce the aspect meanings of the ABS signal.

Red Stop! Train on next block 
Amber Train on block after next; proceed with caution
Green Normal speed; next two blocks are unoccupied

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7.1 Route Establishment ] [ 7.2 Train on Line ] 7.3 Release of Route ]

R. Jayanthan
Last updated on 01 January, 2002