Couldn't people just choose to drive at 55 if they wanted to save gas without it being enforced?
My limited experience of driving in the States saw people overtaking whatever the limit, or below.
Also, most interstates etc have space for people to easily overtake anyone wishing to stick to the limit.
Regardless of the speed limit posted, people will speed if they want I guess.
I doubt it would go down too well to use enforcement to tell people to drive slower than they have gotten used to, certainly where roads have previously been, say 65 or 75.
