In message , Clive
writes

Sorry, but this makes no sense to me. You can't set the signal to red
before the train passes it in case the train stops at the signal.

It sounds like you're misunderstanding how overlaps work. These are,
indeed, 183m (200 yards) on ex-BR and speed-related on LU.
Maybe I phrased it wrongly. Whilst I agree about the overlaps, a
separate circuit set the signal to red, independent of the track
circuit, after about one and a half cars had passed the signal.

From my training: There is an additional block joint known as the
'replacement block joint' which replaces a signal to danger even though
the train hasn't actually reached the section being protected by that
signal. This is so that the signal can't show a green aspect behind a
train.

This applies to LU - I'm not familiar with the 'big trains' to know if
they do the same, although from my limited experience it's not uncommon
for a signal to still show green after a train has passed a signal on
Railtrack.
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