The Environmental Protection Agency proposed Tuesday to force tractors, bulldozers and other diesel vehicles that do not run on roads to cut their harmful exhausts by 90% or more.
The new regulations, if imposed after public comment, would have a dramatic impact on air quality, particularly in such pollution-choked regions as Los Angeles and California's San Joaquin Valley.
Although relatively few in number, these vehicles, which are only modestly regulated, account for 44% of the particulate matter, or soot, and 12% of the smog-producing nitrogen oxides from all vehicles nationwide.
"Since tractors and bulldozers are not a common sight on the highway during our daily commute, it may seem that their impact on our air is relatively small," EPA Administrator Christie Whitman said. "Quite the opposite is true."
The EPA's proposal would cut soot emitted from these vehicles by 95% nationwide and smog-forming gases by 90%. The agency predicted that when fully implemented in 2030, the regulations would prevent 9,600 premature deaths and more than 8,300 hospitalizations for respiratory and heart problems each year.
The improvements would be accomplished by requiring engine manufacturers to use state-of-the-art technology in new models and by slashing the sulfur content in the diesel fuel used by the vehicles.
The proposal would require a two-stage reduction in the sulfur levels in diesel, from an average of 3,400 parts per million to 500 ppm in 2007 and 15 ppm in 2010. Diesel engine manufacturers would have to install pollution controls as early as 2008.
The proposal was welcome news in California, where diesel-powered construction and farm vehicles are the largest source of nitrogen oxides and soot, which is linked to asthma attacks, cancer, endocrine disruption, heart and lung illnesses and premature death.
In California, these vehicles spew 644 tons of nitrogen oxides a day into the air, said Jerry Martin, spokesman for the California Air Resources Board. By contrast, only 528 tons come from all light-duty passenger vehicles, which include cars, small pickups and vans. The big diesel-powered vehicles also emit more than twice as much soot as cars and other light vehicles.
"This is a big win for us," Martin said. "It is probably the best environmental gift we have gotten from the federal government in several years."
California had already started to regulate the pollution from these vehicles, but the new proposal would enable the state to go much further. California now requires that the sulfur level in diesel be no higher than 500 ppm, which would be the federal standard from 2007 to 2010.
But the state was prevented by law from requiring pollution control devices on most construction and farm machinery. It had been lobbying the federal government for years to make a proposal such as the one presented Tuesday.
The proposal would go a long way toward helping California reach air quality standards for smog and soot, Martin added. He said this would be particularly needed in and around Los Angeles, where construction vehicles are common, and in the San Joaquin Valley, where farm machinery pumps pollution into the air. The two areas have the worst air quality in the nation, according to the EPA.
Boston and downtown Manhattan have had tastes of what the future could be like if this proposal were implemented.
At the beginning of Boston's "Big Dig" highway tunnel project, hundreds of construction vehicles spewed black smoke into the air around apartment buildings, hospitals and office buildings downtown. The state required contractors to fit much of their equipment with pollution control devices.
"For those who live and work directly next to the project, it really improved quality of life," said Coralie Cooper, transportation program manager of Northeast States for Coordinated Air Use Management, an association of eight northeast states' air pollution programs.
And Boston's requirements were not nearly as tough as the ones in the new EPA proposal.
Concerns about the air quality near the site of the World Trade Center after the Sept. 11 attacks prompted a widespread public outcry.
Studies showed the biggest health risk was posed by diesel exhaust from the construction machinery and trucks and buses in Lower Manhattan. City and state officials required contractors to use ultra-low sulfur fuel and fit their equipment with pollution controls. The air quality data from this program, which is not yet available, may help determine the impact of EPA's proposal.
Whitman said the annual cost of the proposal, estimated to be $1.5 billion, would be far outweighed by the annual savings of more than $80 billion in medical expenses.
Manufacturers of off-road engines withheld their comment on the proposal while they studied its implications.
"We're not quite sure if we like it," said Ken Golden, spokesman for Deere & Co., which manufactures engines for construction, farm, forestry and other vehicles that would be regulated by this proposal.
Environmental groups, which have been routinely critical of the Bush administration's environmental policy, showered praise on Whitman.
"Administrator Whitman deserves enormous credit for her leadership in crafting a proposal that would dramatically lower the most harmful airborne contaminant in our environment," said John Balbus, Environmental Defense public health program director and physician.
"Diesel exhaust contains a host of harmful contaminants that together pose a cancer risk greater than that of any other air pollutant, and that contribute to unhealthy levels of smog and fine particles affecting millions of Americans," he said.
The proposal adds to significant steps that Whitman has already taken to reduce harmful emissions from diesel trucks and buses, recreational vehicles and school buses.
It mirrors a Clinton administration policy to cut emissions from diesel buses and trucks. That policy was frozen, with many other pending or new regulations, after the Bush administration took office. As one of her first decisions in office, Whitman decided to embrace it.
These diesel rules, if they survive a comment period that ends Aug. 20, will complement regulations aimed at cleaning up exhaust from gasoline engines that were adopted under the Clinton administration.
"We have now addressed the full fleet of on-road and off-road vehicles," Whitman said.