After declaring back in 1993 that it wanted only clean air vehicles, The Los Angeles County Metropolitan Transportation Authority (Metro) has finally retired its last diesel-powered bus. It is believed that Metro is the first public transportation authority in the world to run only alternative-powered vehicles.

The long journey for the fleet, which includes 2,221 compressed natural gas (CNG), one electric, and six gas-electric buses, has not ended, though.

“We expect CNG to be the base fuel stock for the next three to five years,” says John Drayton, vehicle acquisition manager for Metro. “The next step we'll likely see is battery technologies improving. [But] when you look at natural gas, it's a very nice fit for a fleet like ours that returns” to a central facility each night.

Metro, which moves nearly a million passengers a day, uses a fast-fill system that fills a single bus in less than eight minutes, Drayton says. The buses, which are a mix of models from Neoplan, New Flyer, and North American Bus Industries, stay in service for about 12 years, or 500,000 mi.

“We run a very severe-duty cycle,” he points out, with the average speed of a bus at about 11 mph operating under constant stopping and quick starting. Each bus runs about 50% idle time, he says, and it's not uncommon to put 4,000 hours on a single engine each year.

Because of this wear and tear, bus engines do require a lot of maintenance, and the CNG engines are no different, generating as much as 10-15% higher maintenance costs. “There's more maintenance effort, although that gap is closing as we get more [2010-compliant] engines,” Drayton says.

California's journey to clean air started many years ago. “We were universally known as the smog capital of the world in the '60s and '70s,” Drayton says.

In 1989, Metro began testing alternative technologies. In 1993, California passed an alternative fuel initiative and the authority made the decision to purchase only alternative-fueled vehicles going forward.

CHANGING AN IDENTITY

Metro's first experience was with a methanol-powered bus, but because that fuel does not have any lubricity, the engines were taking a beating, Drayton says. “We were changing engines every 20,000 mi.,” he points out, adding that Metro expects an engine to last 300,000 mi. So, the choice of CNG seemed to be the right decision, even back then.

“Next to hydrogen, [CNG] is the cleanest fuel stock out there,” Drayton says. The buses, he notes, cost about 50% less to run on CNG right now than diesel fuel.

Drayton estimates the cost to run a CNG bus at about 30¢-40¢ per mile, including a 50¢/gal. federal tax credit that is available - a credit that is worth close to $30 million a year to Metro. The authority expects the CNG fleet to reduce particulate matter by 80% and eliminate 300,000 lbs. of greenhouse gas emissions per day. And because the storage tanks for the fuel are on the roofs of the vehicles, there is no diminished carrying capacity.

“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.”

Drayton says the authority will continue to look at advancing technologies, including all-electric models, fuel cells and other possibilities, but he sees refinement of current technologies, including exhaust technologies, to be the more short-term answer.

“We think at some point eventually we'll go to electric vehicles,” he says, “but it's anybody's guess. The best experts think that's five to ten years away. We need to see a 300-, 400-mi. operating range before it might be viable to our service.”

Fuel cells hold greater promise, he says, but the extremely high cost is a major drawback for an organization that is partially beholden to taxpayers.

Metro has a number of other energy-saving initiatives, including the installation of solar panels, which have reduced its carbon footprint by 16,500 metric tons in 2010, it says.