Someone asked a similar question in the “Ask Mr. Green” advice column for Sierra Magazine…I’ll copy it here from their website:
Hey Mr. Green,
What’s best for the environment, continuing to drive my perfectly fine 1990 Honda Accord, or trading it in for a new gas-sipping Prius? — Heath in Los Angeles
Well, Mr. Green hates to say this because you might be bonded to your trusty old Accord, but she burns twice the petrol and wheezes out twice the global-warming gas of a Prius or similar hybrid model. Being a conscientious environmentalist, though, you’re also worried about the energy and pollution involved in building a new car — the equivalent of 1,000 gallons of gas. But by the time the Prius hits 50,000 miles, its energy savings will have made up for its own construction. So unless you drive very little, a new hybrid is the way to go.
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so, Skeeter…I guess the best thing would be to figure out the mileage that the used non-hybrid Honda Civic will get (as opposed to a Prius), figure out how many miles a year you drive, and how many years you plan to keep the car. If the Prius would save you more than 1,000 gallons of gas over that time, then it would be better for the planet to buy the Prius. Unless, of course, you take the money you’d save by buying a used car instead of a new one, and donate it to environmental groups instead ;)