When I decided to go green about this time last year, my goal was to see how much an average guy could reduce his carbon footprint—that new cultural holy grail that has replaced reducing your cholesterol—without spending an arm and a leg or becoming an obnoxious ecoterrorist. It is only fitting, then, that for this, the final chapter in my year-long experiment, I took on the most blatant of emissions culprits: my car.

First things first. Both my and my wife’s vehicles—a 2001 Jeep Grand Cherokee Limited and a 2005 Audi A4 convertible—are paid for. Footprints and gas prices aside, trading in a depreciated but perfectly drivable car for a new one was a serious proposition. Moreover, as a middle-aged male Texan, my automobile is all tangled up with my ego and self-image. I had standards to uphold: If I was going to drive something smaller or slower, it would have to really make good on the green front.

So I devised a central conceit for my dealership wanderings: “something sporty that gives me forty.” That is to say, I wanted a car that a typical eighteen-year-old would be proud to pick up his date in and that averaged 40 miles per gallon on the highway. I began my search by going to greenercars.org and looking up “Greenest Vehicles of 2008,” a list of the twelve automobiles that merit a superior “green score” from the American Council for an Energy-Efficient Economy, a formulation that takes into account not only miles per gallon but also reduced emissions of greenhouse gases and other noxious pollutants. (For more information, consult aceee.org.)

I soon found out just how difficult this search was going to be. On my first foray, to a Honda dealership, I ran across one model that met the fuel-economy challenge: the Civic Hybrid, which gets a nifty 45 mpg on the highway, has a high green score of 57 (the best rating for all 2008 cars), and costs $23,550. Unfortunately, when I kicked the tires and slipped behind the wheel, I felt an inescapable sense of déjà vu. The car was technologically leaps and bounds beyond the original “compacts” of the seventies, but it still had the look and feel of a cheap import—in other words, it struck out on the sporty front. In fact, so did the other three Hondas (the Civic GX, the Civic, and the Fit) listed on greenercars.org. “I’d never buy one of those,” I muttered as I left the dealership in my gas-guzzling Jeep. Snobbery? Yes. Allowing a sophomoric sense of cool to overcome my less-developed sense of green? You bet. But surely, I thought, there’s a car out there that looks every bit as snazzy as a Dodge Viper and still delivers the efficiency and footprint goods.

My demands continued to make the pickings slim. I dropped by the closest Ford dealership to test-drive a Focus (about $15,000), the hot new compact considered to be the great green hope of the American auto biz. Unfortunately, they had none in stock. “We can try to give you a call when a few come in,” said a salesman. “But they’ll be sold by the time you get over here.” (Memo to automakers: It’s difficult for drivers to go green if they can’t find greener cars in stock.) The Mini Cooper Clubman ($21,000) was sporty enough, but its mpg (37) didn’t quite measure up. The Toyota Prius provided the mpg (45), but its blimpish design was just too nerdy, even for an old guy. Besides, like a lot of hybrids, it doesn’t pay for itself nearly as fast as it should. The Prius would cost me at least $22,000; my trade for the Jeep (19 mpg) would be just under $5,000. A calculator at edmunds.com broke it down simply: It would take me 196 months to break even and begin saving money on gas. Yeah, so I’d be doing the environment a big favor for those sixteen years. But it’s important to distinguish between reasonable sacrifice and dumb investment.

The last model I tried, the Smart Fortwo—a glorified golf cart with a three-cylinder engine—came the closest to my sporty-and-forty requirement. This little bug gets 41 mpg on the highway, 33 mpg in the city (green score: 49), and has a kind of anti-muscle car, geeky-chic vibe to it. And at roughly nine feet long and five feet wide, with a five-speed transmission, it is both tiny and quick (max speed of 90 miles per hour, cruises nicely at 70 miles per hour). Test-driving it, I was reminded of my Volkswagen Beetle days in college and a few years beyond. I loved my Beetle, really, more than any car I’ve ever owned, because it could be comprehended by the mechanically challenged. The Smart car wasn’t the brawny model I’d been envisioning—but might I revive my love for small cars with this new “beetle”? Maybe. At least I could conceive of buying one, particularly considering the price tag (just under $12,000) and that, according to the online emissions calculator I’ve been using all year, I’d be reducing my footprint by a significant 11 percent, or 6,276 pounds a year. It would certainly be useful as an errand or short-commute car.

Then again, since my feeling is that the best technology for both greening and the greenback is yet to come, maybe I’ll just wait a few years for a Tesla Roadster: The all-electric Maserati-looking muscle car, which just entered into production this year, goes from 0 to 60 in 3.9 seconds, gets 224 miles per charge, and has zero emissions. True, it is built-to-order and is being waited on by such VIPs as George Clooney, who’ve already plopped down the total $109,000 retail sum. But if Tesla eventually mass-produces the car and the price goes down to, say, $50,000 or so—hey, it’s not that unlikely—I might just jump on it. More important, if Tesla and its inevitable competitors can manufacture lower-line models with the same technology, we might finally be talking about a brave new world of fossil fuel-free driving.

In the meantime, the fact that someone is not presently moved to trade his Jeep for a hybrid doesn’t mean he should have his driving privileges revoked by the Green Police. My wife and I are doing the best with what we have. First, we drive her Audi as often as possible, as it gets 28 mpg (it’s also very, very sporty). We try to limit use of the Jeep to road trips and stops by Home Depot, which I estimate cuts down my annual mileage by about 2,000 and my footprint by 2,071 pounds, all while saving me as much as $265 on gas (see “Progress Report”). Second, on the highway we are adamant about sticking to the 65-mile-per-hour speed limit, since driving just 10 miles per hour faster can lower our fuel economy by 10 percent. Third, we watch our tire inflation, because for every three pounds we go below the recommended pressure, our fuel economy drops by about 1 percent. All told, these simple actions theoretically enhance our cars’ efficiency by 11 percent.

This is one of the primary lessons from my first year of greening: While you do sometimes have to spend money to save money—if you remember, I invested $4,500 in attic insulation and window treatments to reduce my home’s energy waste—some savings involve only a behavioral investment. And though changing one’s ways can be a pain (composting is still unpleasant), the effect on one’s carbon footprint can be relatively dramatic. Take my year’s quest as a whole: My investment was $10,350, and my savings was $2,250, a figure that will only increase exponentially. As for my footprint? I brought it down by 35 percent, or 23,452 pounds.

Going green has taught me that you really can do well by doing good. And if a stubborn old guy can take this sort of environmental living seriously, then there’s hope for all of us. Even if it means waiting for that Tesla Roadster.

Progress Report:

This month’s effect on my carbon footprint, wallet, and happiness.