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Typical permissive signals that can be found on lots of places in Belgium |
Permissive signals in both directions
There are two basic line lay-outs for the bi-directional permissive signalling.
a) The oldest one: All permissive signals are released.
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b) In the new lay-out all the signals of the wrong main running are lock until needed to clear for a train.
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In the example below the line is in the normal state. Two trains are waiting to be signalled to the main line.
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The exit route of the first train is released. The first train gets a green light without speed limitation.
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When the train passes the main signal, the signal restores its default state.
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The junction and the first block is cleared. Now the second train gets a free way. Speed in the junctions is restricted to 40 km/h.
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The train approches the next junction. The main signals only open progressively although the runway can be already set.
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When the second train passes the main signal, it restores its default state.
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