Average fuel efficiency of a US vehicle has improved only three miles per gallon since the days of the Ford Model T.
According to Ford, the Model T – which began mass-production in 1913 – averaged a fairly healthy 25 miles to the gallon. Nonetheless, by 1923, the year the study begins, the average fuel efficiency of the entire US fleet was 14 mpg. That figure remained about the same for more than a decade
From 1935, however, fuel efficiency fell into steady decline, dropping to an alarming 11.9 mpg in 1973
From 1974 the economy of the US fleet improved five miles a gallon to 16.9 mpg in 1991. Curiously, since then – despite growing environmental awareness and publicly-voiced concern – improvement has been painfully slow, reaching just 17.2 mpg in 2006
The article then goes on to claim, it is the older cars on the road that are part of the problem.
Well, cash for clunkers didn't improve that situation much, if at all.
Perhaps the issue really is, that Automakers and Big Oil like poor fuel efficiency. It keeps everyone happy and profitable.