In a gathering hosted by the Diesel Technology Forum at U.S. Environmental Protection Agency headquarters in Washington, D.C., the manufacturers displayed their next generation of cleaner-burning trucks.

"We are using white handkerchiefs to demonstrate that the exhaust from these six clean diesel trucks contains no smoke or visible soot," said Allen Schaeffer, executive director of the Diesel Technology Forum.

Schaeffer´s group represents engine and vehicle manufacturers, diesel fuel refiners and makers of emission control devises.

EPA Administrator Stephen Johnson was on hand for the diesel engine demonstration. "Through innovations in technology, this economic workhorse is expanding into an environmental workhorse," Johnson said.