WASHINGTON — EPA Administrator Stephen L. Johnson is happy with the progress made by engine makers in meetings the agency’s newest round of tough emission standards.

Johnson has reviewed vehicles that meet EPA rules for new truck and bus engines, which cut emissions of smog-causing nitrous oxides by half and lower emissions of particulate matter by more than 90 percent.

“Together with the Diesel Technology Forum, EPA is meeting the president’s call to get our nation off the treadmill of foreign oil dependency by advancing the technologies that are good for the environment, good for our economy, and good for our energy security,” said Johnson. “For the past century, diesel engines have been America’s economic workhorse — reliable, fuel efficient, and long lasting. Through innovations in technology, this economic workhorse is expanding into an environmental workhorse.”

Johnson discussed the science behind clean diesel technology in Washington this week with the many executives on hand from the fuels, trucking, engine, and environmental communities. Johnson also witnessed a “white handkerchief test” on the exhaust as a demonstration of the improvement in diesel’s environmental performance.

EPA’s clean diesel program uses a “systems approach,” in which cleaner fuels help enable cleaner engine technologies. The program is nearing a key milestone. On June 1, 2006, refiners and importers must ensure that the sulphur content of at least 80 percent of the volume of the highway diesel fuel they produce drops from the current level of 500ppm to 15ppm. Lowering the sulfur content will enable modern pollution-control technology to be effective on the 2007 trucks.

Once these fuel and engine regulations are fully implemented, 2.6 million tons of smog-causing nitrogen oxide emissions will be reduced each year. Soot or particulate matter will be reduced by 110,000 tons a year. An estimated 8,300 premature deaths, 5,500 cases of chronic bronchitis and 17,600 cases of acute bronchitis in children will also be prevented annually.

Diesel engine makers — including Caterpillar Inc., Cummins Inc., Detroit Diesel Corp. and Volvo Trucks North America — each had engines on display and said they were on track to meet the ’07 standards, which will be more stringent for particulate emissions.