Dan Ariely makes a good point: why do we talk about miles per gallon, when gallons per 100 miles would be a much more useful and intuitive measure?
The primacy of mpg as a metric means lots of attention paid to things like the Progressive Automotive X Prize, which will give $10 million to the first team to come up with a viable 100mpg car. But the amount of gas saved by moving from 30mpg to 100mpg is about 2.3 gallons per 100 miles, while the amount of gas saved by moving from 15mpg to 30mpg is about 3.3 gallons per 100 miles. If we are to save gas, it’s much better to concentrate on building more attractive cars in the 30-40mpg range than to strive to reach the 100mpg goal.
Update: Bialik is on the same page.