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JEFF JACOBY

The paradox of fuel efficiency

IT DIDN'T take Hurricane Katrina to move the issue of fuel efficiency into the spotlight. For decades, automakers have been urged to produce, consumers have been urged to drive, and the government has been urged to mandate more fuel-efficient cars. If the vehicles on our roads got more miles to the gallon, we have been told again and again, we could dramatically reduce the amount of oil we depend on -- and from that would flow benefits equally dramatic:

America's foreign policy would be strengthened, it is said, since we would no longer have to appease the unsavory regimes that control most of the world's crude oil. The economy would surge as money now spent on fuel was channeled to more productive uses. Mother Earth would be better off, since less fuel would mean less pollution and less drilling for oil. And at a time of $3-a-gallon gasoline, motorists would have particular reason to rejoice: Higher-mileage cars would need fewer expensive fill-ups.

Late last month, with Katrina still days away, the Bush administration proposed new regulations mandating improved gas mileage for pickup trucks, minivans, and some SUVs. Transportation Secretary Norman Mineta said the plan would save 10 billion gallons of gasoline by 2011. Critics dismissed his proposal as either trifling (''almost embarrassingly inadequate" -- Eric Haxthausen, Environmental Defense), or dangerous (''higher fuel efficiency standards increase traffic deaths" -- Sam Kazman, Competitive Enterprise Institute). But the basic idea -- that higher fuel efficiency can mean lower American gasoline use -- no one seemed to challenge.

If better mileage had political sex appeal before the hurricane, it had even more of it afterward. In Boston, Mayor Thomas Menino called a press conference to announce that the city's 450 diesel-powered cars would be replaced with more-efficient vehicles that run on biodiesel fuel. He promised to trade in his mayoral SUV -- a Ford Expedition -- for something smaller and more fuel-efficient. Then, ''as television cameras rolled," The Boston Globe reported, ''he climbed into the Public Health Commission's new Ford Escape hybrid SUV and drove away across the plaza."

Lawmakers have gotten into the act too. A bill introduced in the Massachusetts Legislature would shower benefits on drivers of fuel-efficient vehicles. Among them: a $2,000 tax deduction, the right to drive solo in carpool lanes, and lower fees at parking meters.

All of which might be worth considering if using fuel more efficiently really would result in less fuel being used. But it won't. It will result in more fuel being used.

If that sounds counterintuitive, think about it this way: Would lowering the price of operating an automobile -- i.e., making driving cheaper -- lead to higher or lower consumption? Higher, of course: The cheaper something is, the more of it we generally want. Cars that run more efficiently make transportation cheaper by getting more miles out of each gallon of gas. Result: more miles driven and more gasoline consumed.

If that still sounds counter-intuitive, think about computers. Consider how much more use you get from your computer today than you did from the far less efficient PC you owned 15 years ago. As the efficiency of computers has climbed, so has the demand for them. Today it costs less than ever to process a byte of data by computer -- but more resources are devoted to computing than ever before. Driving is no different. If American cars averaged 45 miles per gallon, it would take less fuel than it does now to move a car from point X to point Y -- but the total amount of driving would rise, and so would the amount of gasoline consumed.

In ''The Bottomless Well," a myth-busting new book on energy and how we use it, Peter Huber and Mark Mills acknowledge that this paradox -- ''the more efficient our technology, the more energy we consume" -- strikes many people as heretical. But the numbers bear it out. Thirty years ago, the energy cost of transportation was nine gallons per 100 vehicle miles. Today it is six gallons -- a 33 percent drop. Yet over the same period, the total amount of fuel consumed rose 56 percent -- from 115 billion gallons a year to more than 180 billion gallons.

This ''paradox of efficiency" is as true of cars and computers as of light bulbs, jet turbines, and air conditioners, Huber and Mills write. ''The more efficient they grew, the more of them we built, and the more we used them -- and the more energy they consumed overall."

None of this is meant as a defense of gas-guzzlers. As the owner of a '99 Toyota Camry who has never driven or owned an SUV, I certainly don't oppose the quest for better mileage. If you have your heart set on a Prius, don't let me dissuade you from buying one. After all, fuel-efficient cars do have their advantages. Reducing American dependence on oil just doesn't happen to be one of them.

Jeff Jacoby's e-mail address is jacoby@globe.com.

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