This should be perfectly obvious, but automotive technologies have changed an awful lot over the last few decades. From about 1975 through 1987, federal standards prompted massive and surprisingly rapid improvements in fuel economy. Cars designers focused on nimbleness and efficiency over raw power, and the fuel savings were enormous.
But since the late 1980s, most engineering advances have focused on making cars more muscular, and fuel efficiency has taken a back seat.
For graphic proof, take a look after the jump at a nifty chart ...