Which is the better choice?
Your decision should be based on expected savings in fuel (amount, costs).
- Replacing a 16 mpg vehicle with a 20 mpg vehicle, or
- Replacing a 34 mpg vehicle with a 50 mpg vehicle
Two researchers, Richard Larrick and Jack Soll, have shown that the public exhibits "systematic misperceptions" when faced with this decision. That is, people tended to choose the second option...did you?
Assume that under both options, you drove 10,000 miles. In Option 1, you would save 125 gallons of fuel, while in Option 2, you would save only 94.1 gallons of fuel.
Their conclusion: "People fail to understand the curvilinear relationship between miles per gallon and gallons per mile (GPM), which suggests that United States car dealers should express fuel efficiency as a ratio of volume of consumption to a unit distance."
Will this ever happen? Probably not, as long as well-meaning consumers remain confused by the mathematics.
Source: R. Larrick & J. Soll's "The MPG Illusion," Science, June 20, 2008, pp. 1593-1594