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[email protected] · May 17th 11, 09:35 AM posted to uk.transport.london

In article ,
() wrote:

*From:*
*Date:* Sun, 15 May 2011 05:19:48 -0500

In article ,
d () wrote:

*From:* d
*Date:* Sat, 14 May 2011 15:23:01 +0000 (UTC)

On Fri, 13 May 2011 19:08:45 +0100
Paul Terry wrote:
I don't understand why the trains run so slowly. 20mph seems to
be the
max in town.

Faster speeds require a greater distance between trains, so if
they ran faster there would be no improvement in frequency
(which tends to be the thing that matters for most people).

Sure, but they run slowly even when there isn't a train in front
for
literally miles because you've just waited 10 minutes for one to
show up.
Even on long sections between kings cross and angel they seem to
trundle
along at their own leisurely pace. I don't understand why they
bothered to
spend all that money on new trains in the 90s if theres no
improvement
in service speed from using them. 15 years is long enough to up
the line
speed.

B2003

The speed limit on the City branch is 35mph (30mph on the CX branch)
Apart from a couple of short level pieces and the very short dip
after City Road and Kings Cross stations, line between Kings Cross
and Angel SB is fairly steep uphill all the way. When motoring, the
train cannot even reach the maximum 35mph allowed (a bit like
running between Camden Town and Bull & Bush).

The 95 stock were slugged on arrival to prevent them being able to
run faster than the 59 stock then on the line. This was supposed to
be removed when all the 59 stock had gone. This was then changed to
"it will be removed when the new signalling comes in".

Apart from the gradient, there are several things which limit how
fast a train can run or can cause delays to a train and one of
these is the infrastructure. There are presently many places on the
older lines (where the tunnels generally followed the layout of the
road above) that force speed restrictions to be in place. On the
Northern line, this is especially noticeable between Kennington and
Moorgate, with permanent speed restrictions of as little as 15mph.
Short of major tunnel realignment (like they did to the SB C&SLRly
through the old siding at Elephant & Castle), there's not much can
be done about that.

Another thing that can slow a train down is the length of the
signal section (the distance a train must travel before a signal
behind it can clear and let the following train proceed). These
vary immensely, from as little as around 100 feet to over 3200
feet. At Highgate SB, the section is a long one and the station
starter will not clear until the train in front has travelled the
equivalent distance from West Finchley to Woodside Park. As a
consequence, there is usually a delay at Highgate SB if one train
is directly following another.
Clapham North NB is another pinch point when following a train, as
the starter will not clear until the train ahead has arrived in
Stockwell platform. Again, this causes a delay to the train in the
platform.

Whilst these delays might be short, they add up over the line.
Where there is the equivalent delay between stations, a driver,
knowing they are following a train and can see the red signal
ahead, will normally drive at a slower speed in order to give the
train ahead time to clear the section and thus avoid actually
stopping at the signal. This also means that the driver doesn't
then have to make a P.A. within 30 seconds of the train stopping -
at least that way the train is still moving, even if it's only at a
few mph.

This is something where new signalling can make a difference
because the sections can be much shorter because the speed of the
train will automatically be reduced as necessary to still retain
the braking distance. This will mean that the frequency can be
improved because the trains can get closer together if required.

Roger

" behind it can clear and let the following train proceed). These
vary immensely, from as little as around 100 feet to over 3200
feet."

Sorry, slight typo" - that should have read"around 500 feet to over 3200
feet"

Roger