"M J Forbes" wrote in message
oups.com...
So is that to imply that there's no tripcock-equipped lines that are
signalled for bi-directional working? Or if so, is there some
technical gubbins that will lower the "wrong-direction" cocks when a
train is running wrong line?

The back tripcocks remain operational at all times - indeed instances of
trains being "back-tripped" are quite common, mainly due to obstructions on
the line.

On bi-directional lines, trainstops reading in the wrong direction will be
automatically lowered as the train approaches, and will raise again when the
train passes to provide protection. There are still problems with certain
reversing movements, however...

As an example, if an 8-car train of A stock reverses eastbound in the Circle
Line platform at Baker Street, the sequence is as follows:-
1. Westbound starting signal cleared, train shunts forward far enough to
fit behind the eastbound starter (w/b starter change to red once front of
train passes it).
2. T/Op cuts out tripcock at that end, and changes ends.
3. Eastbound starting signal cleared and train departs east, rear trip
striking the now-raised trainstop at the westbound starter, but with no
effect because cut out.
4. Tripcock cut back in next time train driven from that end.

As can be seen, problems often arises not with the wrong-road starter, but
with other signals.