What sets the speed in CTRL tunnels through London?

On Fri, 5 Sep 2008 03:27:59 -0700 (PDT), Boltar
<boltar2003.uk> wrote:

>On Sep 5, 11:06 am, Michael Bell <mich...@beaverbell.co.uk> wrote:
>> Eurostars go through Kent at 180 mph, so we are told. Then they slow
>> down to 14 mph in the CTRL tunnels in London. Why?
>>
>> Is 140 mph simply "the next notch down" on the signalling system?
>>
>> Or is this limit set by air resistance in the tunnels?
>
>Its only 100mph in the channel tunnel. Must be something to do with
>air pressure.

I thought it was about paths?

On Sep 5, 11:06 am, Michael Bell <mich...@beaverbell.co.uk> wrote:
> Eurostars go through Kent at 180 mph, so we are told. Then they slow
> down to 14 mph in the CTRL tunnels in London. Why?
>
> Is 140 mph simply "the next notch down" on the signalling system?
>
> Or is this limit set by air resistance in the tunnels?

Its only 100mph in the channel tunnel. Must be something to do with
air pressure.

B2003

Boltar wrote:
> On Sep 5, 11:06 am, Michael Bell <mich...@beaverbell.co.uk> wrote:
>>Eurostars go through Kent at 180 mph, so we are told. Then they slow
>>down to 14 mph in the CTRL tunnels in London. Why?
>>
>>Is 140 mph simply "the next notch down" on the signalling system?
>>
>>Or is this limit set by air resistance in the tunnels?
>
> Its only 100mph in the channel tunnel. Must be something to do with
> air pressure.

I thought the speed in the channel tunnel was to do with pathing, that
if they went faster, they'd take up more Eurotunnel paths.

Robin

Mike Roebuck wrote:
> On Fri, 5 Sep 2008 03:27:59 -0700 (PDT), Boltar
> <boltar2003.uk> wrote:
>
>> On Sep 5, 11:06 am, Michael Bell <mich...@beaverbell.co.uk> wrote:
>>> Eurostars go through Kent at 180 mph, so we are told. Then they slow
>>> down to 14 mph in the CTRL tunnels in London. Why?
>>>
>>> Is 140 mph simply "the next notch down" on the signalling system?
>>>
>>> Or is this limit set by air resistance in the tunnels?
>> Its only 100mph in the channel tunnel. Must be something to do with
>> air pressure.
>
> I thought it was about paths?

It's certainly paths in the chunnel itself, since it has to be shared
with the shuttle and freight trains. Dunno about other tunnels on
non-shared lines, though.

Mark

The design was for a 230kph speed - so, as Graeme Wall states, it is
due to the curvature (both horizontal and vertical) and cant. IIRC the
tunnel sizing is a limiting factor but not sure to what extent.

Also I believe E*s have set speed bands so that they can normally
operate at certain speeds.

Further I think the speed reduces further between Stratford and St
Pancras, presumably the result of the acceleration profile for a E*.

HTH

OC

On Fri, 05 Sep 2008 03:27:59 -0700, Boltar wrote:

>> Eurostars go through Kent at 180 mph, so we are told. Then they slow
>> down to 14 mph in the CTRL tunnels in London. Why?
>
> Its only 100mph in the channel tunnel. Must be something to do with air
> pressure.

I too would have thought a limiting factor was air pressure, also the
pressure wave the train produces in such a confined space, that it would
heat the surrounding air and need even more ventilation.

On Fri, 05 Sep 2008 12:28:49 +0100, Mark Goodge
<usenet@listmail.good-stuff.co.uk> wrote:

>Mike Roebuck wrote:
>> On Fri, 5 Sep 2008 03:27:59 -0700 (PDT), Boltar
>> <boltar2003.uk> wrote:
>>
>>> On Sep 5, 11:06 am, Michael Bell <mich...@beaverbell.co.uk> wrote:
>>>> Eurostars go through Kent at 180 mph, so we are told. Then they slow
>>>> down to 14 mph in the CTRL tunnels in London. Why?
>>>>
>>>> Is 140 mph simply "the next notch down" on the signalling system?
>>>>
>>>> Or is this limit set by air resistance in the tunnels?
>>> Its only 100mph in the channel tunnel. Must be something to do with
>>> air pressure.
>>
>> I thought it was about paths?
>
>It's certainly paths in the chunnel itself, since it has to be shared
>with the shuttle and freight trains. Dunno about other tunnels on
>non-shared lines, though.

Sorry, yes, my response was to the comment about the Channel Tunnel
only. I should have snipped the rest.

On Sep 5, 11:06 am, Michael Bell <mich...@beaverbell.co.uk> wrote:
> Eurostars go through Kent at 180 mph, so we are told. Then they slow
> down to 14 mph in the CTRL tunnels in London. Why?
>
> Is 140 mph simply "the next notch down" on the signalling system?
>
> Or is this limit set by air resistance in the tunnels?
>
> Michael Bell
>
> --

Did a search on this subject and there was quite a bit of discussion a
couple of years ago. If you put a search for "CTRL Tunnels" on this
group, you'll find them. To summarise, the 140 mph (225 km/h) speed in
the CTRL tunnels came about primarily because increasing the tunnel
cross-sectional area to allow 300 km/h (186 mph) running was not cost-
effective; the time saved between St Pancras and Ebbsfleet by running
at a maximum of 300 rather than 225 km/h (a matter of about four
minutes) could not justify the additional cost of the tunnels.
Remember also that the cost of bored tunnels increases in proportion
to the cube of the diameter, caused mainly by the additional spoil
that has to be removed. This is one reason (but not the only reason)
why London's Tube lines use two single-bore tunnels.

HTH.

On Sep 5, 10:41 pm, Tony Polson <docnews2...@> wrote:
> billetelic_ferroequinolog...@m wrote:
>
> >Remember also that the cost of bored tunnels increases in proportion
> >to the cube of the diameter, caused mainly by the additional spoil
> >that has to be removed.
>
> But the spoil increases according to the square of the diameter,
> not the cube.

Yes, you're right. I stand corrected.

High speed tunnels need to be of a large diameter because of air
resistance. For example, the CTRL North Downs Tunnel is 12m diameter
(twin track) for 300km/h running. Making the London tunnels this big
would increase the cost and there would not be much of a speed
advantage because the train would be slowing down anyway as it
approaches St Pancras. I think the London tunnels are about 6.5m
diameter (single track) and have a 225km/h speed limit.