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[email protected] · May 15th 11, 10:19 AM posted to uk.transport.london

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