"Martin Underwood" wrote in message
...
SNIP

What happened to that set of linked traffic lights on the A4 near Slough
that was programmed to let you through if you drove at 30 mph, but to
ensure
that you hit every red light in turn if you drove slower than 25 or faster
than 35? Does that still exist?

I thought those lights were on the road from Uxbridge.
Baz