"Rod" wrote in message
...


Another exmaple very close to me. Major hill out of town. Became largely
30 mph and rigorously enforced often by mobile speed traps. Result - huge
queues and very slow moving traffic. Change to 40 (yes - it is very rare
to hear of an increase these days) and traffic improves considerably.
Again, I strongly suspect that the 30mph limit, enforced, actually caused
more fuel usage/emissions than the current 40 mph.

The last time I looked at the research it said 22 mph was the optimum speed
for getting traffic through.
I suspect it may appear to have more cars going through at 40 mph but
doesn't actually have more.
Maybe you could do a traffic census or ten to see?