On Mon, 7 Jun 2010 04:56:16 -0700 (PDT) someone who may be D7666
wrote this:-

Speed control relays have been around on LT / LU for eons, they are
nothing new introduced post Moorgate.

Holding a signal and/or train stop at danger and only releasing it
if a train operates track circuit(s) in more than a specified time,
thus proving the train is going slowly enough, was certainly done
before the crash at Moorgate. Sharp curves and approaching signals
with a short overlap are examples. Presumably the way the front of
trains used to enter platforms while the rear of the previous train
was leaving [1] is another example. However, this was greatly
extended after Moorgate to cover dead end tunnels. The original
posting was not so much misleading as incomplete.


[1] IIRC the equipment was fitted as part of 1930s schemes and
removed during the "managing decline" era of the 1970s when it was
thought trains would not need to be run close together again. There
still seems to be some of this, but not as extensive as it once was.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54