I’ve been taking the Santa Monica bus to work for twenty years now. Two years ago I moved to within a mile of UCLA and, while I still bus it,  on nice days I actually walk to work, which should be its own category as it is probably the greenest mode of transport of all, next to biking, and healthy for you as well. When I walk, I not only don’t pollute, but get my 30 minutes of daily required exercise as well.