Diesel Truck Pollution
The Union of Concerned Scientists has also weighed in, issuing a report that points out that although trucks account for just under 6 percent of highway miles driven in the U.S., they account for one-quarter of smog-causing pollution from highway vehicles, a tenth of all domestic oil consumption, over half the soot from highway vehicles, 6 percent of the nation's global warming pollution, the majority of the cancer threat posed by air pollution in some urban areas. According to the EPA, idling trucks and locomotives use 1.2 billion gallons of diesel fuel a year and emit more than 200,000 tons of nitrogen oxides. Talk about idle indulgences -
http://www.ucsusa.org/clean_vehicles/big_rig_cleanup/rolling-smokestacks-cleaning-up-americas-trucks-and-buses.html

Diesel School Bus Pollution Threatens Children
E magazine in July August, 2006,has an article the threats of diesel school buses. http://www.emagazine.com/view/?3251 There is a campaign to reduce the time spent idling by schools. Also soot filters, catalytic converters, newer , cleaner burning engines, the natural gas, and biodiesel all reduce the pollution.
The following article provides more details on pollution from diesel school buses: http://www.ucsusa.org/clean_vehicles/big_rig_cleanup/clean-school-bus-pollution.html