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Donald Marron

How do consumers use engine efficiency? On bigger, faster cars.

Engine efficiency has vastly improved in recent decades, but that has made cars bigger and faster, rather than more fuel-efficient

By Guest blogger / January 7, 2012

Shinzo Nakanishi, chief executive and managing director of Maruti Suzuki poses with company's new compact SUV XA Alpha car after unveiling it at India's Auto Expo in New Delhi January 5, 2012. Marron argues that innovations in engine efficiency haven't improved fuel economy, but they have made cars bigger and faster.

Adnan Abidi/Reuters

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Auto companies have made great strides in improving engine efficiency in recent decades. But those improvements haven’t done much to improve the fuel economy of America’s passenger car fleet. Instead, consumers have “spent” most of those efficiency improvements on bigger, faster cars.

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Donald B. Marron is director of economic policy initiatives at the Urban Institute. He previously served as a member of the President's Council of Economic Advisers and as acting director of the Congressional Budget Office.

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MIT economist Christopher Knittel has carefully quantified these tradeoffs in a recent paper in the American Economic Review (pdf; earlier ungated version here). As noted by Peter Dizikes of MIT’s News Office: 

[B]etween 1980 and 2006, the average gas mileage of vehicles sold in the United States increased by slightly more than 15 percent — a relatively modest improvement. But during that time, Knittel has found, the average curb weight of those vehicles increased 26 percent, while their horsepower rose 107 percent. All factors being equal, fuel economy actually increased by 60 percent between 1980 and 2006, as Knittel shows in a new research paper, “Automobiles on Steroids,” just published in the American Economic Review.

Thus if Americans today were driving cars of the same size and power that were typical in 1980, the country’s fleet of autos would have jumped from an average of about 23 miles per gallon (mpg) to roughly 37 mpg, well above the current average of around 27 mpg. Instead, Knittel says, “Most of that technological progress has gone into [compensating for] weight and horsepower.”

This is a fine example of a very common phenomenon: consumers often “spend” technological improvements in ways that partially offset the direct effect of the improvement. If you make engines more efficient, consumers purchase heavier cars. If you increase fuel economy, consumers drive more. If you give hikers cell phones, they go to riskier places. If you make low-fat cookies, people eat more. And on and on. People really do respond to incentives.

The Christian Science Monitor has assembled a diverse group of the best economy-related bloggers out there. Our guest bloggers are not employed or directed by the Monitor and the views expressed are the bloggers' own, as is responsibility for the content of their blogs. To contact us about a blogger, click here. To add or view a comment on a guest blog, please go to the blogger's own site by clicking on dmarron.com.

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