Efficiency seems to equate to more money spent by the American public.
Check it out:

A federal appeals court ruled Friday that a group of California companies cannot sue to stop the Environmental Protection Agency’s (EPA) efficiency and greenhouse gas rules for heavy trucks.

The decision keeps in place the federal government’s first rules on truck efficiency and greenhouse gases, which the EPA developed jointly with the Transportation Department’s National Highway Traffic Safety Administration (NHTSA) in 2011.