On Tue, 08 Mar 2005 00:05:00 +0000, Michael Hoffman
wrote:

Robin Mayes wrote:
[Michael Hoffman]:

As to why they are used, I guess it's either to divert flows in the
peaks to cope with the numbers or because some routes are closed at
certain times, e.g. an exit closed after 23:00.

Interesting guess. Does anyone know?
Correct guess.

Can you give any examples of where I would see this in action then? I'm
particularly interested in the diverted flows during the peaks aspect.

London Bridge currently has diveted flow during the peaks, but I don't
know offhand if they're using switchable signs.