In article , Tom
Anderson writes
According to http://www.trainweb.org/tubeprune/signalling1.htm,
signals are linked to the overlap between them and their section, as
well as to the section itself (the overlap, being part of the previous
section, is also linked to that section, of course). If that's true,
there can never be anything between a green signal and the end of its
section, in the overlap or not. Thus, it is always safe to go up to
full speed at a green signal. No?

No.

In some situations it's as you described:

|-O 6 |-O 4 |-O 2
-------+---A---I-------B-------+---C---I-------D-------+---E---I--

6 green requires A, B, and C all clear.
4 green requires C, D, and E all clear.

But on plain line there's unlikely to be separate track circuits, so
it's more like:

|-O 6 |-O 4 |-O 2
---------------I------------X----------I------------Y----------I--

6 green requires X clear.
4 green requires Y clear.

I don't believe there are any photos on my web site showing it, but I've
certainly seen a signal stay green after a train has passed it until it
reaches the overlap block joint. On the Silverlink lines there are
places where, because of this, a single class 313 can disappear around a
bend before the station starting signal goes back to red.

--
Clive D.W. Feather | Home:
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