There really is no excuse for 30 years of innovation... for gas mileage to have gone down.
The only way this works is if cars remain exactly the same while improving only the engine technology. In 1981, the Honda Accord was 175" long, 64: wide and weighed 2,083 lbs. The 1.8L engine made 75hp. A current Accord is 191" long, 72" wide and weighs 3,287 lbs. Its 2.0L engine makes 154hp. The power-displacement ratio of the engine went up by 84% but the weight went up by more than 50%. As long as people want faster/bigger/more we will eat up any efficiency gains to have more comfort. Only when forced will the average person use efficiency to decrease consumption.