GM's turn in the barrel

I have to wonder how much pollution is estimated to come from vehicles, as opposed to chemical companies, power companies, manufacturing, etc. Seems its easier to put strict regulations on vehicles, which may or may not be the primary cause of pollution, and ease up on commercial enterprises.

We have gotten to a point where the air is substantially cleaner, and that is something for which we should all be grateful... but to make the regulations more and more draconian doesn't seem like the right way to do it.