Is it more energy efficient to buy a used car or new Prius?

 Slate Magazine addressed this question in an article today and did a decent analysis.  They compared the estimated energy to produce a Prius and the energy consumption over 172,500 miles of burning gasoline to the amount of energy consumed burning gasoline over the same distance for a used Toyota Corolla.  The conclusion was that even with the added manufacturing energy for a new Prius, over the 172,500 miles it uses 22% less energy than the Corolla due to its higher fuel efficiency (and the Corolla is no slouch in this category either).

However, one flaw I found in the analysis was that you're probably not going to drive a used car 172,500 miles.  That's some pretty heavy use.  So I did the same calculation, but over a 100,000 mile lifetime.  I found that the new Prius still consumes about 7% less energy than the used Corolla over that period.

The break-even point is at 81,000 miles for a 30.5 mpg car, or to get a car equivalent to the Prius that gets around 37 mpg (non-existent).  So unless you're planning on buying an older used car that will last for less than 81,000 miles, you'll consume less energy by buying the Prius.

Then, once your 81,000 miles are up, you can buy another used car, but your total energy consumption will still surpass that of the new Prius (this is why Slate did the comparison over 172,500 miles - basically the assumption is that if your used Corolla dies, you buy another).  So if your main concerns are energy consumption and the environment, go with the more fuel efficient new car (or used one, if you can find it).  Economics are a seperate issue, of course.

Great post & I agree this was an interesting article.

My concern with the article was this: it treated used cars as if there was no energy consumption from their manufacture.

True, used cars have already been manufactured, so you aren't directly causing the car manufacturer to manufacture 1 more car for you.  But people are willing to buy new cars--Corollas, Camrys, VW bug, whatever--in part because they can be resold.  If you buy one of those cars, you are adding to their resale value--and to the likelihood that future people will buy Corollas, Camrys, or VW bugs, knowing that they can "trade it in" in 3 years for a new one.

I'm not saying that's evil--just that it's not quite right to think about "used" cars as having no production effects.

A better methodology might be to pro-rate the production effects of a car over its (expected) lifetime.  If a VW bug typically lasts 120,000 miles, and you buy it at 40,000 miles--well, you're responsible for 2/3 of the production effects.  If a Toyota Corolla typically goes 180,000 miles and you buy it at 60,000...same thing.

That way we count the actual impact of our purchases on manufacturing, and cars that tend to last a long time get counted the right way.

That's a very good point.  After all, if you're buying a used car from a person, that person will likely also be buying another car - if not a new one, then a used one, and the person they buy that car from will be buying another car....somebody along the line will be buying a new car.  So I like your pro-rating idea to reflect that.

Forgive me if this is not well thought out- I haven't had much sleep lately- but if everyone goes out and buys new Priuses and all the still usable cars just go to the junk yard, you will have to create a lot more cars than are necessary, and there will suddenly be hundreds of thousands of still usable cars going to the junk yard.  I think it's important that people buy used cars- reduce, reuse, and recycle.  Yes, maybe a bit more energy is consumed.  But it's not just about energy.  What about the materials needed to make a car?  What about the environmental damage done by mining for the needed metals?   What about landfill space and chemicals leeching into the soil?  I am sure there is more, but you get my drift...I don't think it's fair to pro-rate the production effects evenly.  People buying new cars should be held more reponsible than those willing to reduce and reuse.

Well for one thing, not everyone is going to go out and buy a new car.  For a lot of people that's not an option for economic reasons.  This discussion just applies to the people with the option of buying a new $20k car.

I also tend to be a little one-track minded on the subject, because while I agree that we need to reuse materials as much as possible, energy translates into greenhouse gas emissions, and I think global warming dwarfs other environmental problems.  If a bunch of cars are going to the junkyard, people will recycle much of the materials, and in the meantime, the average emissions from our cars have decreased.

So are you admitting that it would be a bad thing if everyone *did* buy a new car?  ;)

In terms of energy usage and emissions, you are better off not driving at all.  Ride the bus, ride your bike, live within walking distance, carpool.   Somewhere else on here I posted about the fuel efficiency of buses versus cars.  A bus only needs 4 people on it to be as fuel efficient as your average car, and buses are going to drive around whether you are on them or not!  Plus then you aren't requiring any energy to manufacture a car, to transport your fuel from the oil fields to the gas station, etc.

Yeah, that would be bad.

And sure it's better to take public transportation than drive a car.  But that's not what this article was about ;-)

And I agree, if you are going to buy a new car, it should be something like a Prius.  I just don't know that buying new is 100% better than buying used...