http://www.etrucker.com/apps/news/article.asp?id=65347
It will be a few years before this takes effect.
However I see a problem. For example, if we're allowed to carry 90,000 lbs within the future, our fuel mileage will go down, but our ton-mile per gallon used will go up. Our trucks will actually be more efficient.
What's needed is BSFC standards. BSFC is how much fuel it takes to make one horsepower for one hour. This is very standard stuff, and the lower number(less fuel) is better. Since horsepower requirements vary so much, this is the way to go.
I'd have no problem with congress adopting BSFC specific CAFE standards. I do have a problem with them adopting across the board MPG standards. It just plain doesn't make sense. Should peterbilt be punished for their 389?