I don’t know why politicians assume our time is less valuable than the small savings in gas consumption that would be achieved with this? Oh wait, I do understand: they work in government.
My 07 GTI gets much better mpg going 75mph then it does going 55, the car was designed and geared for higher speeds. On a long distance trip averaging 75mph I would get roughly 32mpg, on that same trip doing 55mph I would get 26mpg. I have tried many different speeds to find the optimal speed for my car, at 85mph the car gets 34mpg.
How about we do like the japanese did, tax vehicles on engine size and occupancy capabilities. A 2L engine would pay say a base of $200 a year where a 6L engine would pay $600. They also factor in the vehicles weight but I am not sure how exactly.