Make your SUV into a low emissions vehicle

Where I live there is a high proportion of environmentalists. With such a high number you'd think that when looking at traffic there would be less SUVs and more small and hybrid cars - remarkably there isn't. In fact I've never seen so many Hummer's in my life. People love there SUVs, they commute 40-50 miles (1-3 hours depending on traffic) each way to work in their Hummer or Explorer or Suburban. There's a new idea coming out of the University of Pennsylvania - buying emissions credits, which thus make your vehicle a low emissions vehicle and thus the large amount of junk coming out of your tailpipe is nullified. It's an interesting idea. I found it also interesting that it's not the SUV owners that are buying these credits. Odd, truly odd (or as somebody I know would say awd).