A Green Hummer?
Tai Robinson showing his converted Hummer to schoolchildren in Kansas

As oxymoronic as it sounds, there's at least one out there and it's driven by former U.S. national skier Tai Robinson. After converting his Tacoma truck to run on a combination of gasoline, hydrogen, and compressed natural gas for the alt.vehicles Drive to Survive convoy across the country last year, Tai, who's based in Utah, has upped the ante by converting the notoriously ungreen Hummer in similar fashion — this time removing the dirty diesel and adding veggie oil to the mix. "We took what is arguably "the dirtiest" [most unpopular] vehicle on the planet and almost doubled the miles per gallon."
Green Hummer

Even after the conversion, you can argue it's still pretty lousy gas mileage at around 18 miles to the gallon. Tai's response is to show people that what comes out the tailpipe after his work is magnitudes cleaner than before.
"We still need to conserve, but it no longer matters what vehicle you drive, what's important is the fuel you choose to run your car on. I would like people to drive what they want and still be doing something good for the planet."
Those who come up to the Hummer bristling with anger, says Tai, leave a lot more satisfied that it's running on clean, safe, renewable fuels. "Trying to burn Hummers or ban them is destructive. They aren't responsible for asthma in children. Burning gasoline and diesel fuel is the problem."
Close-up of Green Hummer
Tai now makes a living with his father Fred converting other people's vehicles to clean the air, including one they recently did for the Angels Nest Retreat, a sustainable living and education center in New Mexico. He's also talking to Arnold Schwarzenegger's camp about converting his personal army of them.
Tai got more involved in cleaning up the worst polluters after the birth of his first child. "After my son, Charlie, was born I made a choice to do something now to give future generations a chance of a healthy, happy place to live. When Charlie says to people 'My dad's truck cleans the air,' I just melt."