The garbage may still stink, but the trucks hauling it through Seattle streets will soon be a lot cleaner.

The two garbage- and recycling-collection companies that contract with the city, Waste Management and Allied Waste, are outfitting their 180 diesel trucks with smog-reducing equipment and promising to cut the amount of sulfur emitted by their fuel, steps that could go a long way toward cutting their pollution.

The move is the latest in a regional effort to trim diesel emissions — a major source of the area's unhealthy air.

"For quite some time this is something we've wanted to help make happen," said Dennis McLerran, executive director of the Puget Sound Clean Air Agency, which oversees air quality in King, Pierce, Snohomish and Kitsap counties. "I'm really, really pleased that this is coming together because these are the kind of trucks that are operating out in the neighborhoods every day."

For several years, local school districts and government agencies in the region have installed filters on the exhaust systems of diesel vehicles, and filled fuel tanks with an ultra-low-sulfur fuel.

But this is the first time private companies have agreed to such extensive measures for their trucks, albeit entirely with money from the city and the clean-air agency, McLerran said.

Mayor Greg Nickels said he hoped the project would set an example for other businesses.

"We would like to see many of the larger diesel fleets consider this," he said. "And that's one of the reasons we're making this happen."

Seattle Public Utilities is spending $425,000 for the emissions equipment and $25,000 per year for fuel upgrades. Seattle City Light is spending $50,000 for biodiesel for some of the trucks, part of its effort to curb emissions of carbon dioxide and other gases linked to global warming. Puget Sound Clean Air is contributing $50,000 for the anti-pollution equipment.

The measures are expected to cut emissions of harmful particles by more than 50 percent, and cut the emissions of toxic chemicals by up to 70 percent, McLerran said. Some vehicles also will have additional filters that cut the emissions by as much as 90 percent.

All of the trucks will be fitted with devices in the exhaust systems that help break down toxic chemicals and particles. Allied Waste, which serves South Seattle, has begun using a mixture of ultra-low-sulfur fuel and biodiesel, made from soybeans, to power the trucks.

Waste Management, which serves North Seattle, won't use the biodiesel mix because its trucks also serve other North King County cities, and Seattle didn't want to pay for its use outside the city, said Hans Van Dusen, a contract manager for Seattle Public Utilities.

But Waste Management will start this year by using a fuel additive to cut down on sulfur emissions.

Starting next year, federal regulations will require all on-road diesel vehicles to use ultra-low-sulfur fuel.

Warren Cornwall: 206-464-2311 or wcornwall@seattletimes.com