16 C.F.R. Part 306: Automotive Fuel Ratings, Certification and Posting
The current system's usefullness is in providing a comparison between vehicles. The actual miles per gallon (mpg) is not necessarily accurate, but its limitations are probably applied equally. To accomodate alternate fuel vehicles, mpg should be replaced with cost per mile. The cost of fuels in this calculation should be retail cost of the fuels at government facilities on January 1 of the year of manufacture of the vehicle. The other two pieces which would be useful would be a cost per mile graph at various speeds on level ground, and a cost per hour at idle.