Report finds old school buses among the worst polluters.

Aging school buses spew harmful diesel fumes across the United States, according to a report based on federal and state data, and major funding is needed to address the problem. The report released Wednesday by the Union of Concerned Scientists found the nation's 505,000 school buses are some of the oldest and dirtiest vehicles on the road. More than a third have been in use for more than a decade, and a single bus can produce between twice and 10 times as much diesel soot as a big rig.