In message , Dave Arquati
writes
but what I have always wondered is how does New
York manage to run a 24-hour service, or is this because they can often
re-route trains if they want to close a section of line (very muddling
for visitors!), which we can't do in London?

Because some New York lines have four tracks (for fast/slow trains) of
which one pair can be used for all services at night. So theoretically
engineering on Finchley Road - Wembley Park or Barons Court - Acton
Town needn't close the line (although I'm sure the HSE would disagree).

I've seen them doing maintenance of the Atlanta Marta (which is similar
to a Met/District Line style of urban commuter railway) late in the
evening by working on one track and having alternate-working on the
other. No doubt the UK's safety mafia would disallow this!!

The trains run from about 5am to 1am.
--
Roland Perry

In article , Roland Perry
writes
I've seen them doing maintenance of the Atlanta Marta (which is similar
to a Met/District Line style of urban commuter railway) late in the
evening by working on one track and having alternate-working on the
other. No doubt the UK's safety mafia would disallow this!!

Alternate working requires a sufficiency of crossovers to switch trains.
The tube lines don't have these, in general.

There's also a problem with trainstops - they need to be lowered to
prevent a train running the wrong way from "back-tripping". Except where
bidirectional working is allowed (e.g. at termini) this isn't designed
into the signalling.

--
Clive D.W. Feather | Home:
Tel: +44 20 8495 6138 (work) | Web: http://www.davros.org
Fax: +44 870 051 9937 | Work:
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In message , Clive D. W. Feather
writes
Alternate working requires a sufficiency of crossovers to switch
trains. The tube lines don't have these, in general.

A design fault, then.

There's also a problem with trainstops - they need to be lowered to
prevent a train running the wrong way from "back-tripping". Except
where bidirectional working is allowed (e.g. at termini) this isn't
designed into the signalling.

Another fault.

[These are excusable when the tubes were originally designed for normal
working hours. I think we forget how little of life was 24x7 as recently
as 30 years ago. I could certainly drive from Cambridge to Chelmsford at
midnight and see no other car on the road. At some point this changed
radically - perhaps the tubes need to keep up.]
--
Roland Perry

In article , (Roland
Perry) wrote:

In message , Clive D. W. Feather
writes
Alternate working requires a sufficiency of crossovers to switch
trains. The tube lines don't have these, in general.

A design fault, then.

More a concept fault for tube tunnels. Not a problem with cut-and-cover
tunnels but then London's tubes aren't based on them.

--
Colin Rosenstiel

In message ,
Colin Rosenstiel writes
More a concept fault for tube tunnels. Not a problem with cut-and-cover
tunnels but then London's tubes aren't based on them.

Most of the "Underground" system is either above ground, or in
twin-track cut and cover.
--
Roland Perry

In article , (Roland
Perry) wrote:

In message
, Colin
Rosenstiel
More a concept fault for tube tunnels. Not a problem with cut-and-cover
tunnels but then London's tubes aren't based on them.

Most of the "Underground" system is either above ground, or in
twin-track cut and cover.

Not in Zone 1 though.

--
Colin Rosenstiel

In message ,
Colin Rosenstiel writes
Most of the "Underground" system is either above ground, or in
twin-track cut and cover.

Not in Zone 1 though.

No, but being able to run 24x7 round the Circle, and on many of the
lines outside, would be much better than nothing.
--
Roland Perry

In article , Roland Perry
writes
[These are excusable when the tubes were originally designed for normal
working hours. I think we forget how little of life was 24x7 as
recently as 30 years ago. I could certainly drive from Cambridge to
Chelmsford at midnight and see no other car on the road. At some point
this changed radically - perhaps the tubes need to keep up.]

The answer, of course, is cost. Digging new crossover tunnels isn't
cheap. Signalling changes are cheaper, but is it a better way to spend
the money than running night buses instead?

--
Clive D.W. Feather | Home:
Tel: +44 20 8495 6138 (work) | Web: http://www.davros.org
Fax: +44 870 051 9937 | Work:
Please reply to the Reply-To address, which is:

In message , Clive D. W. Feather
writes
Digging new crossover tunnels isn't cheap.

I wouldn't suggest new tunnelling.
--
Roland Perry

In article , (Roland
Perry) wrote:

In message , Clive D. W. Feather
writes
Alternate working requires a sufficiency of crossovers to switch
trains. The tube lines don't have these, in general.

A design fault, then.

There's also a problem with trainstops - they need to be lowered to
prevent a train running the wrong way from "back-tripping". Except
where bidirectional working is allowed (e.g. at termini) this isn't
designed into the signalling.

Another fault.

[These are excusable when the tubes were originally designed for normal
working hours. I think we forget how little of life was 24x7 as
recently as 30 years ago. I could certainly drive from Cambridge to
Chelmsford at midnight and see no other car on the road. At some point
this changed radically - perhaps the tubes need to keep up.]
--
Roland Perry

This will gradually change when new signalling systems come in, although
the shortage of crossovers will be the restriction. Come movable block
(joint) signalling, trains will just be able to reverse wherever they are
and go back the other way - a sort of signalled wrong direction movement.
Ideal during one unders, security alerts etc.

Roger