SAN FRANCISCO -- Even garbage in San Francisco is going green -- thanks to Monday's announcement that the city's entire fleet of garbage and recycling trucks were running on alternative fuel.

As of March 19, more than 400 garbage collection vehicles were running on alternative fuels, according to Norcal Waste System Inc. spokesman Robert Reed.

This will cut greenhouse gas emissions by 5,400 tons per year, a 21 percent decrease from when the trucks were using only diesel.

The three companies that work under the umbrella of Norcal Waste System Inc. - Sunset Scavenger, Golden Gate Disposal & Recycling and S.F. Recycling & Disposal, Inc. - started experimenting with alternative fuels in 2001 when they built a liquefied natural gas filling station, Reed reported.

The pilot program for the alternative fuel fleet consisted of eight transfer trucks and five collection trucks.

The remainder of the fleet was switched over in March and the trucks run on liquefied natural gas or biodiesel B-20, a blended fuel, which is 20 percent biodiesel and 80 percent low-sulfur diesel, according to Reed.

"San Francisco adopted aggressive goals to reduce citywide greenhouse gas emissions," Jared Blumenfeld, director of San Francisco's environment department said in a statement. "By operating their entire truck fleet on alternative fuels Sunset Scavenger and Golden Gate are helping to fight global warming as well as improve the quality of life in San Francisco," he added.