Re: CTRL speed reduction in tunnels?

IIRC the maximum speed in the Thames and London tunnels will be
240km/h. As with most things in life, the maximum sustained speeds in
tunnels are a compromise. There are many factors involved:

Areodyanmic effects are considerable as a train travelling in a bore is
like a loose fitting piston in a cylinder. Above certain air pressures
and rates of change of air pressure, problems can be caused to the
auditory canal of the personnel and passengers causing discomfort at
least or actual injury.

Aditionally, the larger the ratio between the bore and train frontal
area, the higher the pressure will be and the higher the velocity of
the vortex. This also causes additional drag on the train requiring
more energy to sustain any given speed.

In an ideal world, you would build a very large bore compared to the
size of the train and everything except the construction costs would be
fine and dandy. As building any tunnel is extremely expensive, the
tendency is to minimise the bore size of the tunnel consistent with
maintaining passenger comfort, speed, energy and vortex velocities.

Naturally, you can tweak any of these factors and trade off a desired
result against the others. For example, you could build pressurized
trains (aka DB's ICE1) to allow for smaller tunnel bores, so long as
you are prepared to put up with more expensive train maintenance for
the whole life of the rolling stock. Or you could use piston relief
ducts as per the channel tunnel which reduce air pressures by
interconnecting the two single bore running lines at intervals to even
out the pressure pulses. These cost money and have to be fitted with
fire dampers to prevent ingress of smoke into the unaffected bore, thus
increasing the ongoing infrasructure costs.

A further complication for CTRL is the limited range of speed codes
available within the TVM430 signalling which was a given for this
particular project. Essentially you have the choice of 300km/h,
270km/h, 240km/h then 160km/h and so on. (Brian Williams gave an
excellent description of the TVM speed codes a little while back on
this group). 160km/h was too slow, 270km/h and above would have
required either larger bore sizes or some very clever pressure relief
devices, all making the costs rise substantially, so the best
compromise in this case was 240km/h.

Initial discussions for the CTRL stock anticipated a 270km/h top speed
to avoid wasting paths on the CTRL itself, but this was scaled back
when it was realised that for the Ebbsfleet and north Kent line
services, nearly all of their time on the CTRL would be limited to
240km/h.

The higher gearing for 240km/h also meant that the amount of current
drawn by the CTRL DS on the DC network would also need to rise in order
to maintain comparable rates of accelleration to a 375 and thus not
waste paths on the conventional network.

So, compromise on size and equipment within the tunnels and that fitted
(or not) to the trains, their capex and opex lifetime costs, the fact
that the trains have to be a best fit compromise on two totally
different types of railway infrastructure and chuck in a few givens
like TVM speed codes and government dictated journey time targets and
viola la 395. A decidedly non standard train.

Anyone who thinks they are buying a train off the shelf for this
application is living in cloud cuckoo land. Sure, bits of it like the
traction drive may be well proven, but like most other trains, I
predict that it will largely be an assembly of proven subsystems from
the best of previous breeds, bolted to a bespoke bodyshell and then
integrated.

Saying this is an off the shelf product is akin to stating that you can
build a complete Ford Focus by buying all of the required parts from
your Ford Dealer's spares counter and then getting the workshop to
assemble it with the complication that you're going to use the previous
model's rear suspension becuase it was better.

This approach is the only realistic one which can be adopted when you
supply a small build of a bespoke product to a customer with particular
requirements, I can't think of any other realistic production
methodology for stop-start orders for a country which doesn't/can't buy
a standard European product such as a Siemens Desiro DMU (exported to
many EU countries in standard form).

Where previous EMU and DMU builds have fallen down has been in
integrating all of the subsystems to make a whole which works day in
and day out and certain breeds of modern EMU and DMU have been better
than others in this respect. However, one thing we can be sure of is
that the Japanese will give particular attention to this area or they
may (quite literally) have to fall on their sword.

The class 66 on the other hand (and OT as far as the original post
goes) is a now established standard product which is being sold all
over Europe, having been developed by the N Americans (USA and Canada)
for the Brits. Sort of reminds you of large quantities of N American
maunfactured vehicles spreading over Europe some 60 years ago.......

Richard

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