SACRAMENTO – The California Air Resources Board (ARB) has expanded its roadside testing of smoking diesel trucks and buses by requiring owners of two or more vehicles to conduct annual anti-soot tests on their fleets.

The Board adopted the new testing program, which will affect up to 120,000 trucks and buses a year beginning January 1995, after a day-long public hearing in Sacramento. Owners of only one vehicle or fleets licensed in other states are exempt from the self-inspection, but ARB officials stressed that those vehicles are still subject to the random roadside test, which includes all diesel-powered heavy-duty trucks and buses that are driven in the state.

While the majority of vehicles that are tested at roadsides are "bi-rigs" and large buses, the new self-inspection program will also include many large delivery vehicles that are used almost exclusively in cities.

Fleet operators will conduct the tests themselves with equipment that measures the density of smoke and the vehicles must meet the same anti-soot standards as those that are used in the random roadside testing of diesel vehicles, which began November 1991. The density of smoke is measured while the engine is revved to full throttle, simulating a rapid acceleration. Engines with smoke density or opacity greater than 55 percent -- emissions that are three or four times greater than when the engines were new -- would require repairs. Fleet operators will be required to keep records of the tests they do for at least two years and will be audited by ARB enforcement staff.

The new testing is expected to reduce particulate-like soot emissions by 10 percent a year (eight tons per day) by targeting the dirtiest vehicles that produce the majority of pollution, either because of tampering or lack of maintenance. In the year since the roadside testing began, approximately 4,500 trucks and buses have been issued citations by the ARB's nine roving teams of inspectors, resulting in approximately $1.5 million in fines while the required repairs have reduced the number of smoking trucks by about 26 percent. Emissions from many of these trucks and buses have been reduced by as much as two-thirds as a result of those repairs, which often also improves fuel economy.

 "Diesel soot emissions are the single largest cause of the public complaints we receive," said Jananne Sharpless, ARB chairwoman to describe the Board's concern. "In addition, this pollution can cause grave health problems deep in the respiratory system and some of those particles can carry potentially cancer-causing compounds, as well.

 "The roadside tests are a major effort to reduce that pollution by targeting the dirtiest trucks and buses just like we do in the Smog Check for cars. Expanding the tests to include another 120,000 trucks and buses that aren't often found on the inter-state highways will benefit public health even more."

 The ARB's program to control diesel soot has all the same types of controls that are imposed on passenger cars, including standards that require the world's cleanest new diesel engines for 1993, cleaner diesel fuel standards and the Smog Check-style tests.

The ARB has adopted emission standards that require essentially "soot-less" new engines for trucks and buses, cutting emission levels by more than 90 percent from those in place just five years ago. To comply with those standards, manufacturers are now delivering new model buses and trucks that are equipped with new technology that filters soot from diesel-powered engines while some models are equipped with engines designed to run on clean-burning natural gas and methanol.

The ARB also has set clean-up standards for reformulated diesel fuel, which will reduce emissions from all diesel trucks and buses on the road, by 25 percent when it is available for sale no later than October 1993.