"Peter Campbell Smith" wrote in message

"Recliner" wrote in
:

If the bogies are very near the car ends, then the effect is close to
articulation. But with the circular profile of Tube tunnels, I'm
certain that reasonable sized open gangways are not feasible without
true articulation. If you look at the relative movement of Tube car
ends, you can see just how difficult it would be -- look at how much
smaller the gangway is compared to the outer body in S stock and
378s in order to accommodate all the movement.

If cars have shared bogies, or bogies very near the ends, the centre
throw will be greater than with the current placement of the bogies.
Given the tight fit of tube trains in their tunnels I would imagine
that that would give a clearance problem on curves - unless you go
for substantially shorter (and more) cars, like the Space Train.

On the Waterloo and City they solved a similar problem by grinding
part of the flanges off the tunnel lining segments, but as I recall
the Victoria Line has concrete linings without flanges.

I had a look this morning at the width/height issue, and 3 average
height people can stand side-by-side in the vestibule area facing
along the car. So I think a wide gangway would probably allow two
people to pass, provided the gangway was about as high as the
internal car body.

The carriages in an articulated train will certainly have to be shorter,
roughly the spacing of the bogies in a conventional carriage (just as
Eurostar carriages are). That would be needed both for clearance reasons
as you say, and also to keep the axle loading down. In fact, it may be
made particularly short to allow for wider carriages, unless the linked
carriages are mounted on extended pivots, rather than the shared bogie.

With non-articulated stock with conventionally spaced bogies, there's a
lot of relative movement at the car ends on entry to curves, which the
gangway bellows have to absorb. This makes them thicker, and reduces the
gangway width. The same is true in vertical direction. So if you were to
try and install open gangways on a train like the 2009 stock, the
gangways would be very very cramped (narrow and low).