ALPHARETTA, Ga. -- Over-the-road buses and trucks with 2007 engine technology run nearly 90 percent cleaner than required by federal emission standards for diesel particulate matter, a new study has determined.

The study, partly funded by the U.S. Department of Energy and prepared by the nonprofit Coordinating Research Council in Alpharetta, also found that other pollutants were cut much more sharply, in some cases 99 percent cleaner than previous engine systems.

The findings could be useful to those bus companies that operate 2007 and newer motorcoaches, and market their buses as being environmentally friendly. In effect, their coaches are much "greener" than the law requires.

"These engines were significantly below the 2007 standards for most pollutants," Jeff White, director of emissions research and development for the Southwest Research Institute, the organization that carried out many of the tests, told a leading trucking publication.

The Coordinating Research Council worked with the Health Effects Institute of Boston, and the Southwest Research Institute in San Antonio.

The report is titled "Phase 1 of the Advanced Collaborative Emissions Study" and focuses solely on over-the-road truck and bus engines.

The study examined exhaust emissions "from four 2007 model-year, heavy-duty diesel engines manufactured by Caterpillar, Cummins, Detroit Diesel and Volvo," the report said.

"More than 360,000 of these heavy-duty trucks and buses were sold in 2007 and 2008, which is why this report is so important," said Allen Schaeffer, executive director of the Diesel Technology Forum, an organization that promotes diesel technology.

The report said the research was undertaken "to quantify the reduction in both regulated and unregulated emissions from advanced diesel engines."

The research found the engines far surpassed the main focus of EPAs 2007 regulations, a diesel particulate matter limit of .01 grams per horsepower hour, or g/hp-hr. The engines actually registered .0011 g/hp-hr, which the report said was 89 percent below the 2007 requirement.

Heavy-duty engine makers added diesel particulate filters to their exhaust systems in 07, and refined their engines exhaust recirculation systems. The entire package added upwards of $10,000 to $15,000 to the price of a new motorcoach and $7,000 to $12,000 to the price of a new Class 8 truck.

The study found that other EPA-regulated emissions also were much lower than the 07 standards: carbon monoxide emissions were 98 percent below the standard; non-methane hydro-carbons were 95 percent under the mandated level, and oxides of nitrogen oxides were 10 percent lower than required.

White said the four test engines were standard 07 power plants similar to what customers bought. "These were all 2007 production engines," he said.

"Ultimately these findings translate into even greater clean-air benefits for local communities than were previously expected," Schaeffer of Diesel Technology Forum said. "Todays diesel trucks and buses are so clean it would take 60 of todays models to have the same soot emissions as one 1988 model."

Public sector sponsors of the study included the USDOE, the Environmental Protection Agency and the California Air Resources Board. Private-sector sponsors were the Engine Manufacturers Association, American Petroleum Institute and manufacturers of emission-control equipment.

The study showed that emissions not regulated by the EPA also dropped significantly from 1998 and 2004 engines, years in which EPA instituted tougher emission standards.

Unregulated compounds showed a reduction ranging from 38 percent for inorganic ions to 99 percent for hopanes/steranes, elemental carbon and dioxins/furans, the report said. Hopanes/steranes and "elemental carbon" are both petroleum byproducts. The EPA classifies dioxins and furans as possible toxic substances.

Bus, truck and engine makers are gearing up for a new set of standards that go into effect Jan. 1, this time mandating a drastic reduction in NOx emissions.