The vast majority of drivers are paid by the mile, even drivers that own their own truck - but that doesn't mean they drive any slower, mileage based pay means the faster you go the more money you get.
You're not going to get 12-15 MPG out of an OTR tractor with this regulation - they're talking about a 23% increase. Since trucks are averaging 6 MPG right now, they're only talking about increasing to 7.38 MPG - which is VERY doable, and there are truck configurations on the road right now that can get this fuel economy (see my earlier post for some examples of trucks that are available today that I think will either meet or come very close to meeting the new standard).
Also, a big rig (from my own experimentation) gets about the best fuel economy at 55 MPH, dropping sharply off above 60. Of course, driving a big rig at 55 MPH in a state with a 75 (or 85) MPH speed limit is pretty much asking for a rather nasty accident. The rumor in the trucking world is that the state of Nevada actually sued Schneider National several years back for having their governers set to 55 MPH (and the state won). Not sure if that's true or not, since its something I heard in a truck stop.
Of course...
Some days just plain suck - this was the worst MPG I ever saw come out of the truck I was driving. Not sure if it was the cold weather or not, on a warm day the truck would get at least 5 MPG in the same mountainous area of PA.
