Science Policy Forum: Replacing Least Efficient Car Has Benefits for Climate, Wallet

Replacing the least fuel efficient car in your garage may actually save you more money and reduce your carbon emissions compared to buying a new hybrid, said two business professors in a Science policy forum.

Richard P. Larrick, an associate professor of management at the Duke University Fuqua School of Business, and Jack B. Soll, an assistant professor at Duke, wrote that U.S. drivers often evaluate a car's fuel efficiency by comparing their miles per gallon (MPG) rating.

This leads many consumers to believe that the greater the increase in a vehicle's miles per gallon fuel efficiency, the more money they will save at the pump. But, the authors' concluded, the assumption may not always be correct.

Gas consumed driving 10,000 miles. Gallons of gas used per 10,000 miles driven as a function of fuel efficiency of car (expressed in MPG).

Image © Science

Because vehicle fuel efficiency is non-linear, the authors point out, replacing an old rust bucket that gets 16 miles per gallon with a car that gets 20 miles per gallon will reduce your energy costs and reduce climate change-inducing emissions more than replacing a 34-MPG car with a spiffy 50-MPG hybrid model. Assuming that the average person puts 10,000 on their odometer per year, upgrading to your 20-MPG car will save about 31 gallons of gasoline over a switch to a 50-MPG hybrid, they wrote.

The authors are careful to point out that their research should not diminish the importance of highly fuel efficient cars like hybrids, but rather clarify how small improvements can add up to big savings at the gas pump, and much less carbon dioxide in the atmosphere.

As an example of the confusion, Larrick and Soll cite a 2006 New York Times commentary in which the author labeled SUVs with hybrid engines as "fat-free desserts" adding that just "the hybrid car can make people feel as if they're doing something good, even when they're doing nothing special at all."

While the authors in Science agree that "the environment would benefit most overall if all consumers purchased highly efficient cars," they reject the implicit premise that a "small improvement from 12 to 14 MPG [for example] is negligible."

In addition to continuing to offer incentives for purchasing hybrid vehicles, the authors urged policy-makers to direct public opinion towards "removing the most inefficient vehicles . . . [and] make the benefits of greater fuel efficiency more transparent."

Ginger Pinholster and Benjamin Somers

20 June 2008