It is not alleged, but certainly smaller than I expected when you look at volume averaged figures that take into account increased market share of light trucks and other lower mpg vehicles. 23.1 in 1980 and 25.2 in 2005.
SUMMARY OF FUEL ECONOMY PERFORMANCE, MARCH 2005, U.S. DEPARTMENT OF TRANSPORTATION, page 4
24.6 in 1981 (the year cited in the article), and 24.6 in 2004. The peak of 26.2 occurred in 1987.
I'm fine with "alleged," thanks just the same. ;o)