"asdf" wrote in message
...
On Fri, 01 Sep 2006 19:30:03 +0100, Paul Corfield wrote:

I've noticed a small black and yellow stripped plate in the cab
windows
of
Met line trains. Might be in others too, not sure. What are they?

Perhaps this is a silly question and I'll kick myself when I see the
answer, but why would you want to deliberately restrict the speed of
trains in this way (i.e. beyond that required by line speed limits and
the signalling system)? Is it to do with saving energy?

Surely if the trains travel faster, with the same distance between
each train (which is externally determined by the signalling), you'll
have more trains per hour and therefore higher capacity, as well as
improved journey times.

Weak field was (is?) only supposed to be used on longer open air sections of
line, such as most of the Met main and the Hammersmith to Acton Town section
of the Piccadilly. In tunnel sections and most other open air sections of
line, with stations closer together, you would rarely get the opportunity to
reach weak field speeds before starting to brake for the next station.