You mean maybe something like this?
http://ecomodder.com/forum/showthrea...t-20704-2.html
There is a huge difference though, between a 20-40 ton semi getting 7-8mpgs, and a 2 ton SUV getting 10mpg. The semi getting a low mpg number is totally reasonable and proportionate to the job it's doing. Same with a motorhome.
On the other hand, if
Diesel Dave,
JQMile,
Bennelson, and
I can all get in the low 30s in full-size trucks, there is really no excuse for anyone driving something that gets 12mpg as a personal vehicle.
Going from 10 to 12mpg doesn't really "save" you gas, because the other option was buying something that got better than 12mpg to begin with. Its like buying something you don't need on sale, and thinking you saved money because of the sale. You would have saved more by not buying it in the first place.