The Dehli Metro has received the first carbon credits for a rail system in the world. They didn't however do it in a way that people would expect, by taking people out of cars (which they are trying to do), but rather registering the energy saved through regenerative braking of the system. I find that the most fascinating thing about it. Recently there has been news about Sacramento retrofitting their cars to put power back into the grid through regenerative braking but I haven't heard much about other systems doing it. Anyone heard anything about other systems?
I do know that folks in Portland and New York city are looking for ways to capture carbon credits. This might be a better way to start than going after the amount of tailpipe emissions saved by people moving from cars to transit which is often hard to figure out, but should be done eventually. I wonder how hard it would be to retrofit the New York City Subway Cars with this technology?