wrote:
"Peter Corser" wrote in message
...

The platform headwall corner signals are "true" starters. A Vic line
train running in usual ATO mode will not normally pass a red signal
(white aspect shown when an ATO train can pass, but train in manual
cannot).

I was referring to the white aspect in my earlier post, not the red
one. I was wondering why some drivers chose to hold at a station,
even if they have a white aspect.

The same thing is true where signals are ptrovided away from stations
(usually confliction point protection or where there are more than
one route from the signal). Headway posts are not intended to be
stopped at by non ATO trains.

What is a headway post?

The signal is part of the ATP function - it merely tells the driver that he
has the appropriate code and authority to pass that signal, not that he must
pass it. This is identical to a normal procede aspect in manual signalling.
ATO and ATP functions are not fully separated as is usually done with
current systems.

Driver holding at white could be in manual, but may just be running early
(or realise that he is running too close to the one in front - holding at
white for a short period may mean that he can have an unchecked or better
run to the next station/s). If he is running early he will only be held for
time at the next controlled signal site (signals clear on route and time,
among other factors).

Headway posts were installed in the Vic as a means of informing a driver
that he had been stopped in ATO/ATP due to the train in front. These were
the equivalent of intermediate and home signals, but a genuine signal was
only installed where there was a routing consideration. A non ATO/ATP train
could not be signalled to approach a headway post and be stopped at it.

AFAIR the white aspect came up on the corner signal as soon as a 270 code
(medium speed, but allowed remotoring) was available to the train in the
platform. The green was a genuine LUL green - only allowed once the
preceding train had cleared an "overlap" on the next signal (it wasn't
called an overlap, but fulfilled the same function). The codes were 420
pulses per minute = full speed allowed, 270 + medium speed with motoring,
180 = medium speed coasting only, 0 = only used by signalling system.

The station stop was achieved by an initial braking spot followed by a
sequence of spots with the speeds mimicking the braking curve to rest in the
platform. ISTR that the sequence was set in 5 mph steps with the spot
frequency indicating the allowed speed - there were three brake rates with
the braking curve assuming that the "normal" middle rate would be OK. The
only way to easy adjust the curve was reposition a spot (and there was much
fine tuning in the early days).

Peter
--
Peter & Elizabeth Corser
Leighton Buzzard, UK