Yeah natural gas is nice compared to diesel. The EPA concluded that diesel exhaust is not a health hazzard lol. Pretty funny stuff. It contains the same items as smoke, plus more! hehe.
I guess the litter issue is something to think about. I've never understood people with clean ashtrays in their car, tossing butts out the window. Would they toss a butt on their carpet and smash it out? I kinda doubt it..
But really, when theres a anti-something going around, the governments jump right on it because it grabs attention. And while second hand smoke may be bad, not saying it isn't, the exhaust from diesel and gasoline engines is FAR worse.. but I think by now people know that big business gets priority in governments. So it shouldnt be surprising. When was the last emissions standard revision? Nobody knows because it's not an attention grabbing, vote getting headline story.
Check out this story:
http://www.forces.org/writers/kjono/files/epa-ets.htm