On Fri, 13 May 2011 15:31:32 +0100
"Mizter T" wrote:
Think it may have lost its crown of the 'misery line' to the Jubilee these
days but must say that I do still boggle a little when travelling on it
during the high-peak.

I don't understand why the trains run so slowly. 20mph seems to be the
max in town.

B2003

In message , d
writes

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).

Once the line is signalled for full ATO, speeds will improve (but even
20mph is twice the average car speed in central London).
--
Paul Terry

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

On Fri, 13 May 2011 15:20:43 +0100
"Paul Scott" wrote:
Looks like Boltar has missed about three or four years worth of on and off
discussion here explaining exactly what happens at OSIs.

My eyes probably glazed over.

B2003

On 13/05/2011 19:08, Paul Terry wrote:
In message , d writes

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).

Once the line is signalled for full ATO, speeds will improve (but even
20mph is twice the average car speed in central London).

I thought that they were closer to 35 miles. I know that the Northern
Line is 35 miles in central 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

On Sun, 15 May 2011 05:19:48 -0500
wrote:
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".

I don't understand the logic behind that. Surely they'd want the trains to
have the maximum possible performance for when it can be used? eg going up
the steep incline from archway to highgate or the long run from east
finchley to finchley central?

B2003

In message , d
wrote:
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".
I don't understand the logic behind that. Surely they'd want the trains to
have the maximum possible performance for when it can be used? eg going up
the steep incline from archway to highgate or the long run from east
finchley to finchley central?

The signalling may have been designed with certain assumptions in (e.g.
"a train passing Archway at 5mph won't exceed 20mph at signal XYZ").
Changing the train characteristics could invalidate those assumptions.

IIRC there was a collision or derailment near Watford Junction because
modern rolling stock invalidated the signalling design assumptions.

--
Clive D.W. Feather | Home:
Mobile: +44 7973 377646 | Web: http://www.davros.org
Please reply to the Reply-To address, which is:

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

In article , (Clive
D. W. Feather) wrote:

*From:* "Clive D. W. Feather"
*Date:* Mon, 16 May 2011 23:10:06 +0100

In message ,
d wrote:
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".
I don't understand the logic behind that. Surely they'd want the
trains to
have the maximum possible performance for when it can be used? eg
going up
the steep incline from archway to highgate or the long run from
east
finchley to finchley central?

The signalling may have been designed with certain assumptions in
(e.g. "a train passing Archway at 5mph won't exceed 20mph at signal
XYZ"). Changing the train characteristics could invalidate those
assumptions.

IIRC there was a collision or derailment near Watford Junction
because modern rolling stock invalidated the signalling design
assumptions.

--
Clive D.W. Feather | Home:
Mobile: +44 7973 377646 | Web: http://www.davros.org
Please reply to the Reply-To address, which is:

Because there's a maximum speed restriction on the line, drivers should
never exceed that speed and, as far as I'm aware, excessive overspeed
isn't normally taken into account (or wasn't). I suppose the existing
signalling could have a "well a driver's never going to be able to get
more than x mph" built into it.

It used to be taught that a signal was always "placed a safe braking
distance" from the train in front, based on train speed, gradient and
weight. However, the Holborn crash proved that wrong and to "safe" was
dropped and it became "placed a braking distance"!

Normally the only time there isn't the "safe" braking distance is at
station starters that have a short overlap and, in theory at least, the
rear of the train in front could be just 100 feet or so away from the red
starter. (In practice, this would only happen if the train in front has
stopped after just clearing the overlap, rather than stopping at the next
signal).

As a consequence, drivers non-stopping a station where trains normally
stop have to reduce their speed to 5mph at the starter. If the starter's
green, there will normally be a sufficient braking distance. However, the
idea is that drivers will always approach the starter as if is at danger,
rather than running full speed only to find it remains red and they go
past the red signal at speed with potentially serious consequences.

I suppose that this could be another reason for not allowing the trains to
run at their maximum power, so that trains can't approach a station any
faster than they can at the moment, but I still can't see it as a real
reason. Perhaps they're just being cautious, or perhaps it's "tidier" to
leave things as they are until the new signalling comes in.
The other thing, of course, is that the update has now taken a lot longer
than originally planned. Perhaps at the time they thought "Oh well, it'll
only be a couple of years by the time everything's finished, we'll wait
until then"!

Roger