Here’s the agency’s press release for the retirement event to be held later this morning:

The last diesel bus in the massive 2,228 vehicle fleet directly operated by the Los Angeles County Metropolitan Transportation Authority (Metro) today was retired making Metro the first major transit agency in the world to operate only alternative clean fueled buses. The “retirement” ceremony highlighted the significant contribution Metro has made in reducing air pollution in one of America’s smoggiest regions.

“What Metro has achieved transcends Los Angeles County,” said Los Angeles County Supervisor and Metro Board Chair Don Knabe. “We proved from both a technical and economic standpoint that a large transit agency can operate with alternative clean burning fuels and this has led many other transit agencies to follow our lead. Likewise, what Metro is doing to tap solar energy, recycle and build green facilities is raising the bar for the industry. That’s good for our customers, taxpayers and the environment.”

Metro runs the second largest public transit bus operation in the United States with nearly 400 million annual passenger boardings, and its buses log just under 1.5 billion miles a year.

Metro directors in 1993 decided to only order clean air vehicles, an action that paved the way for other transit agencies across the U.S. to opt for greener vehicles. After experimenting with methanol and ethanol buses that proved too corrosive for bus engines, Metro ultimately went with compressed natural gas (CNG) engines and today has 2,221 CNG buses, one electric and six gasoline-electric hybrid buses in its fleet. They have logged 1 billion clean air miles.

Compared with diesel buses, Metro’s new CNG fleet reduces cancer-causing particulate matter by more than 80 percent. And because of the switch from diesel to CNG, Metro avoids emitting nearly 300,000 pounds of greenhouse gas emissions per day.

CNG buses cost about 10 to 15 percent more to operate than standard diesel engine buses, largely because of increased maintenance costs; however, the health benefits are immeasurable.

“The American Lung Association in California applauds Metro’s accomplishment in converting their transit fleet from older diesel buses to cleaner natural gas buses,” said Jane Warner, President and CEO for the American Lung Association in California. “By acquiring cleaner fueled buses, Metro is helping to address the region’s serious pollution problems and reduce smog related illnesses and deaths.”

“When I was growing up in Los Angeles, I remember days when the air was too smoggy to go outside and play, and today we understand how crucial clean air is for the health of our kids and communities,” said Los Angeles Mayor Antonio Villaraigosa. “I’m proud that our entirely clean fueled fleet is a key element of greening Los Angeles, and we’re simultaneously improving mobility, customer service and air quality with these new clean fueled buses.”

Metro CEO Art Leahy, who helped spearhead the conversion to alternative fuels while heading bus operations for Metro’s predecessor agency, the Southern California Rapid Transit District, also pointed out that this effort not only is good for the environment but it helps wean America from dependence on foreign oil because vast reserves of natural gas and other fuels exist in North America.

“Metro should be applauded for its leadership in helping to reduce our country’s reliance on foreign oil by powering their vehicles with safe, economical and domestically produced natural gas,” said Hal Snyder, vice president of customer solutions for Southern California Gas Co.

The clean air bus fleet is just one aspect of Metro’s green program which also includes widespread use of solar panels at bus maintenance facilities and other energy saving devices to cut energy costs, recycling, and building and retrofitting new transit facilities with sustainable materials and practices. Installation of solar panels, LED lights and other energy saving features and recycling saves Metro well over $1 million annually in operating costs. The solar panels alone reduced Metro’s carbon footprint by 16,500 metric tons in 2010, the equivalent of removing 3,200 private cars from Los Angeles area streets and freeways.