Is it more energy-efficient to buy a used car than a brand-new hybrid?

Illuminating answers to environmental questions.
July 8 2008 7:29 AM

Green Beaters

Is it more energy-efficient to buy a gas-guzzling used car than a brand-new hybrid?

Brendan I. Koerner chatted online with readers about this article. Read the transcript.

I'm shopping for a car, and my tree-hugging pals are pushing me to get a Prius. But it seems wasteful to buy a brand-new car, given all the energy that goes into the production process. Wouldn't it be greener to get a certified, pre-owned vehicle with decent gas mileage?

A Toyota Prius. Click image to expand
A Toyota Prius

Your query is a serious toughie, as we don't really know how much energy it takes to manufacture a hybrid. Toyota does admit that because the Prius' engine and battery are relatively complex, assembling the hybrid requires more energy than making a similarly sized nonhybrid vehicle. But the company has never quantified that energy premium, so the Lantern will have to rely on an educated guess. If our informed figure is in the ballpark, however, a fresh Prius beats virtually all used competitors—assuming you follow the Lantern's golden rule and keep your car running until the bitter end.

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The best guess regarding the Prius' energy consumption during assembly comes from sustainability engineer Pablo Päster, a Lantern favorite. He used Argonne National Laboratory's GREET model—which takes into account the energy intensiveness of producing glass, steel, copper, and other critical materials—to calculate that manufacturing a Prius requires about 113 million British thermal units. (Päster also guessed that manufacturing the hybrid version of a Toyota Highlander uses 155 million BTUs, vs. 107 million BTUs for the standard Highlander.)

In order to do an apples-to-apples comparison, let's pit the Prius against a car that's frequently cited as its closest nonhybrid equivalent in terms of weight, size, and other specs: the Toyota Corolla. Would it be more energy-efficient to buy a brand-new Prius or someone else's old Corolla? Since certified, pre-owned cars tend to be less than five years old and are refurbished before going on sale, let's generously assume that your used Corolla will last exactly as long as your new Prius: 11.5 years, or 172,500 miles. (The average American discards a car every eight years, but that's more often than necessary: A well-made vehicle will typically last 15 years.)

According to the federal government's 2008 fuel economy guide (PDF), a Prius averages 46.5 miles per gallon (assuming half of a driver's time is spent on city streets and half on the highway). Beyond 172,500 miles, then, the Prius will consume 3,710 gallons of gas. Each gallon contains approximately 124,000 BTUs of energy, so that translates into 460 million BTUs' worth of burned fuel. Add in the production energy, and the new Prius is responsible for a grand total of 573 million BTUs over its lifetime (not including disposal costs).

A Corolla with an automatic transmission, by contrast, averages 30.5 mpg—more than eight miles per gallon better than the average car on America's roads. Over the vehicle's lifetime, that translates into 5,656 gallons of gas containing more than 701 million BTUs of energy. Since the Corolla we're considering is used, we won't add to that total by factoring in production energy.

The Prius is thus the clear winner in this matchup—and, please, no angry letters citing the nickel in the hybrid's battery, an urban legend that the Lantern debunked in March. In fact, a certified, pre-owned car would have to average better than 37 mpg in order to match the Prius' energy consumption over the long haul. And the only nonhybrid cars to achieve such lofty fuel-economy heights are either tiny or diesel-powered. (The Lantern is intrigued by the promise of "clean diesel" technology, and looks forward to test driving the 2009 Volkswagen Jetta TDi, but he sounded a note of caution about it here.)

It's also worth noting that the Prius has another green advantage over the likes of the Corolla: lower tailpipe emissions. According to California's emissions classification system, the Prius qualifies as one grade higher than the Corolla—a Prius is a Partial Zero Emissions Vehicle, while a Corolla is an Ultra-Low Emissions Vehicle.

There are complications to this comparison, of course, beginning with the uncertainty over the figure for the Prius' production energy—it may not take into account certain inefficiencies in Toyota's assembly-line equipment. There are also various wild cards to consider, like whether the Prius' complicated battery would need to be replaced, whether the used Corolla would become less fuel-efficient at an earlier age because of wear, and how driver habits affect fuel economy. (Every time the Lantern quotes the federal government's 46.5 miles per gallon estimate for the Prius, he is deluged with e-mails from Prius owners claiming that this figure is either way too low or way too high.)

The Lantern would be remiss if he didn't bring up the hybrid's price premium. The scales could definitely tip in favor of the used Corolla if you put the $5,000 you saved toward making some critical technological upgrades in your house—for example, converting to an EnergyStar water heater or dishwasher (though, granted, with gasoline at $4 per gallon, the Corolla in our comparison would end up costing you an extra $7,700 in fuel costs over 172,500 miles).