"Tom Anderson" wrote in message
...
How many sizes of tube train are there? Central line trains always feel
tiny compared to, say, circles; and it makes sense that a deep tunnel
might be smaller than a cut-and-cover; is that so? Are
northern/Victoria/Piccadilly any bigger or smaller? How come metropolitan
trains feel so much bigger than circles (as big as real trains), when they
use the same track? Are they bigger, or is it just the decor?

There are two main sizes of London Underground train, the "tube" and the
"subsurface". Subsurface lines are Metropolitan, Circle, District,
Hamersmith and City and East London line. All the others are built to tube
standard. The subsurface lines are about the same size as mainline (ie ex
BR) lines in terms of loading guage. All London Underground trains run on
standard guage track, and use the same electrification system.

Is it
because the northern half of the circle has bigger tunnels? Does that mean
one could run real trains through them? Is there any way to get a train
from, say, the Anglia or Great Eastern lines near Liverpool St down into
the circle?

Certainly in the past it has been possible to run through between what is
now national rail and what is now the London Underground. For example,
there were in the past services along the District side of the circle out
onto the distric line towards Barking that carried on out the LTS line to
Southend. Also in a recent thread someone talked about services from Epping
on the central line into Liverpool St. mainline. Most connections where
they do exist are not very conveninetly possitioned to make inter running
very convenient. There are a few sections where full interrunning is
possible, the main example being the norther end of the Bakerloo line where
the line is shared with tube sized 1972 stock of the district line and
Silverlink class 313 trains of mainline size. I believe it would be
possible to physically fit a WAGN type emu train or Anglia stock onto the
norther side of the circle (I have a vague recollection someone on this
newsgroup has mentioned mk 2 carriages on the circle line at some past
point), but there are no compatible electrification systems and no
convenient track connections for running services.

Does the Thameslink tunnel stop at Moorgate? Does that mean we
could turn the West Anglia into a Retropolitan (tm) line which connected
northeast London with the northern half of the circle? Or take the the met
out to Chingford?

There is no physical connnection between the "widened lines" (that is the
track used by Thameslink between KXSP and Moorgate) and the circle line any
more. The big problem with such a service would be pathing. The London
Underground is at capacity on that route, and any space for such a service
would necessitate a decrease in service on one of the other routes that uses
that track.

If these sorts of things were made to happen, we would end up with a service
on the norther half of the circle a bit like the suburban services in South
london. They would go to a lot of places, but the concept of a London
Underground style "line", with very frequent trains all going on a fixed
route would be lost. A great deal of work has been done in the past to
separate out the bits where BR as was and LU shared facilities so that
interference between service patterns and timetabling could be reduced, and
most people would say that these have been a good thing.

And what's so light about the DLR? It's standard gauge,
after all.

The term "light rail" tends to mean "modern trams or systems using that
technology" eg Metrolink, Tramlink, Supertram ... in various cities in
Britain, and similar systems in other countries. What makes the DLR light
rail is the vehicles, which are derived from a German tramway herritage, and
the tramway type track. Look at some of the curvature in the line through
the isle of dogs, and you will appreciate that this is not the same sort of
railway that LU or what was BR run.

Could you in fact take one train and drive it willy-nilly over
the entire network? If so, where can i buy second-hand trains? And
finally, is it obvious i spend far too much time in the bloody tube and
have now lost my mind?

You could physically run a train through from most of the London Underground
system to the national rail network, but there's more to it than that. A
lot of london underground stock in the past has been transported on the
national rail network for reasons like delivery of new stock. In such cases
it has run in trains hauled by locomotives with barrier waggons to permit
coupling and braking to be translated from the locomotive to the underground
stock. The reason you can't drive a train willy-nilly over the whole system
is twofold. First of all there is the problem of powering such a train, and
second, there is the problem of signalling. No London Underground lines are
designed to ventilate for diesel engines, and no non London Underground
trains can draw power from the London Underground power system. London
Underground trains to not have things like AWS and TPWS that would be
required for it to drive over the rest of the UK railway network, and even
if they did, they can't get power because nowhere but London Underground
uses that particular power supply. If you built a specific new deisgn of
train that had all the power and signalling systems, and got the relevant
safety cases and permissions and timetabling, it would be theoretically
possible for you to drive it around the whole system.

Thanks,
tom

PS Sorry this has no relevance to oyster

it's to do with transport in London, therefore it's on topic here.

Robin