Oh please: stop whining. We should have clean air! The real issue that no one here seems to address is why don't the Feds help all drivers, o/o's, and companies to install the APU's, NITE systems, or whatever? Last I heard was that a bill to consider a 25% (or 50% at best) rule would be debated in the Congress.
That is it: they have billions for an illegal war, new driving regs that benefit the big friends of Bush & Dems in the transportation industry, but no help to clean up the air we breathe. How many of us really want to park in a truck stop on a foggy night or in the heat of summer?
Having said that, the biggest polluters on the planet is industry, and the mining/power production & refining plants!