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