The Union of Concerned Scientists last month produced a nationwide School Bus Pollution Report Card that gave the state of Virginia a C for exhaust pollution. No state received an A in the study.

But Thursday, Randall Ray, manager of a company that manufactures school buses, told members of the Virginia Association of Pupil Transportation who were in Roanoke for an annual conference that steps already have been taken to reduce pollutants from school buses and other heavy-duty vehicles.

The Environmental Protection Agency's "2007 Highway Rule" will take effect next year, requiring the use of new engines and fluids that produce cleaner emissions in school buses and other heavy-duty highway vehicles.

That plan requires the use of exhaust systems that break down emissions in a two-part process to reduce harmful particles and the use of ultra-low-sulfur diesel fuel in heavy-duty vehicles.

"The 2007 requirements, from an emissions standpoint, is top-notch," said Ray, a manager at IC Corporation and Affiliated Companies.

The exhaust systems, which will reduce the particulate matter that exits the bus, will look like a bulky muffler and will require little to no maintenance in the lifetime of a bus.

However, there has not been a test run of the new exhaust system on a school bus. Sunny Merryman Inc. -- a bus manufacturer that, like IC Corp., sells buses to Virginia school systems -- expects to fit one of their buses in July.

"We're going to drive that thing all around, but we don't anticipate any serious problems," said Brady Childress, a service manager at Sunny Merryman.

Older buses can be retrofitted with a diesel oxidation catalyst -- a filter that burns particulate matter before it enters the air -- if they contain the right electronics. Ray estimates 1997 models are the oldest buses capable of receiving a DOC.

Danny Carroll, the vehicle maintenance coordinator for Roanoke County Public Schools, and his crew equipped 100 of their 191 buses with DOCs, funded by a grant from the Department of Environmental Quality. Roanoke City Public Schools also retrofitted a number of their buses, but Salem school officials said they would not do so unless it becomes a requirement.

"The expense is just too high, and our budget is too tight," said Mike Bryant, assistant superintendent for Salem City Schools, whose oldest buses are 1983 and 1984 models.

The standing EPA rule is that any buses produced before 2007 will be allowed to run their life span, an average of 12 years, Ray said.

Trucks nationwide began delivering the ultra-low-sulfur diesel to retail outlets on June 1. It should be available for purchase in October; bus fleets have three years to phase the new fuel into use.

Carroll said his transportation department owns six fuel sites, and, one-by-one, they will come into compliance.

"Once we have available tank space, we can start filling them with the ultra-low," he said. "It's not like we can just drain all of the tanks."

Sulfur helps to lubricate bus engines but pollutes the air after it breaks down and exits through the exhaust, much like lead in gasoline for cars. Ultra-low would lessen the amount of pollutants emitted into the air.

Low-sulfur diesel contains 500 parts per million of sulfur; ultra-low contains 97 percent less at 15 parts per million.

Carroll said Roanoke County has been using low-sulfur diesel since it became available in 2004.