Hooray! I was googling all over the place and finally found this interactive tool that steps you though the process of deciding whether it's more eco-friendly to get a more fuel-efficient car or keep the one you've got.
I used it awhile back and remembered it yesterday after learning that the Environmental Protection Agency gives my car a D-minus on air pollution and greenhouse gas emissions. The hybrid Toyota Prius of the same year got an A. So, should I trade mine in for something less polluting?
The thing that I like about this tool is that it's very clear about why this is a tricky decision. Up to 40 percent of the total emissions over the life of a car come from the manufacturing process. So, that's definitely something to consider before you plunk down thousands of dollars on a newly minted hybrid or electric car.
I noticed they've updated it since I last used the tool. Now it seems they encourage you to consider a more fuel-efficient second-hand car if your car doesn't get 55 miles per gallon (that seems really high to me, but I guess there are a lot of fuel-efficient cars out there these days).