My next car? This 2009 Prius is for sale in Bend for $19,570.

Which is the greener choice, buying a new hybrid or continuing to drive your old car? The answer, of course, depends on what your old car is. If it’s a gas-guzzling clunker the decision is easy.

But my old car is a 1990 Acura Integra that gets about 33 miles a gallon (my commute is mostly highway). Although it’s nearing 190,000 miles, it still runs just fine and the mileage is darn good. So what’s the greener choice?

A new hybrid is not as green as it seems, because it takes energy and creates waste to build it. According to analyses done in Japan at Seikei University and at Toyota respectively, anywhere from 12 to 28 percent of the carbon dioxide emissions generated during the lifetime of a gas-powered car occur during its manufacture and transport to the dealer. Electric cars aren’t emission-free either, because you have to consider the impact of producing the electricity used when you plug it in. Although I am generating solar power in the daytime, I would be plugging in my car overnight when I’m drawing juice from Pacific Power.

My old car is already built, so it wins on the manufacturing emissions score. But what if I bought a used hybrid that’s also already built? The hybrid creates more emissions in manufacturing than my Integra did, but they’re both in the past. So going forward, how much would mileage improve with a hybrid and would that improvement reduce my carbon footprint significantly?

At fueleconomy.gov, there is great information to address exactly this question. The carbon footprint score for my Acura is 8.1 tons of carbon dioxide annually. The comparable number for a 2009 Prius is 4.1. So if I ditch the old car and buy the used 2009 Prius, do I keep those 4 tons out of the air? Only if I make sure my car is scrapped or sold for parts. If someone else keeps driving it, that doesn’t improve anything.

So let’s say I scrap the car and buy the 2009 Prius. I save emissions which is good for the planet. I save gas. But I spend $19K. For now I’m keeping my money in my pocket.

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