Mpg drags. Average US feet mpg in 1923 was 14 mpg, 11.9 mpg in 1973, 16.9 mpg by 1991. Only 2% better in 2006 - 17.2 mpg. It's better to focus our efforts on getting a 15-mpg vehicle to 16 mpg, which would save 50 gallons of fuel a year for a vehicle driven 12,000 miles a year, than on getting a 40-mpg car to 41 mpg, which would save only 7 gallons of fuel a year