Once bus engines meant diesel power. Alternative fuels were considered impractical and expensive. But that is changing dramatically. Alternatively-fueled vehicles account for more than 40 percent of ­current U.S. public transit fleets, and 59.7 percent of new buses operate with alternative fuels.

As of 2011, according to APTA’s 2013 Public Transportation Fact Book, diesel-powered buses still lead the sector with 63.5 percent of the U.S. market, but public transit systems are investing in other fueling technologies. (The 2011 data are the most recent available.)

Natural gas (compressed or liquefied) engines power 18.6 percent of buses, hybrid-electric buses account for 8.8 percent, and 8.2 percent use other alternative fuels. While pure electric-powered buses make up just 0.1 percent of the U.S. fleet, they are in the market to stay.

Here are a few examples of public transit agencies investing in alternative fuel technologies.

Los Angeles Metro retired its last diesel bus in 2011. At the time, the agency’s clean-air bus fleet consisted of 2,221 vehicles powered by compressed natural gas (CNG), six gasoline-electric hybrids, and one all-electric bus.
John Drayton, Metro’s vehicle acquisition manager, explained that the effort began in 1988, when the agency (then the Southern California Rapid Transit District) purchased its first 10 CNG buses as part of “a variety of alter­native fuels and technologies including methanol, ethanol, and CNG engines, among others.”

In 1993, the agency’s board of directors adopted an “Alternative Fuel Initiative” that directed staff to purchase only non-diesel buses; CNG has been the fuel of choice since 1995.

CNG was not Metro’s first choice for fueling a bus fleet, however. In 1992, the agency invested in 333 methanol-­powered buses, which Drayton said “proved not well suited to heavy-duty operations like ours.”

Drayton cited both economic and environmental benefits to CNG. “In addition to being a very clean fuel and engine, CNG is currently about 60 percent cheaper than diesel on a cost-per-mile basis,” he explained. “To put it simply, CNG gas is cheap, abundant, and clean. We’re literally saving tens of millions of dollars running on CNG. We also are running some of the cleanest engines in the world.”

But Metro isn’t stopping there. “We are actively looking at further reducing our fleet emissions, and are looking at what is being called ‘near-zero’ as well as ‘zero-emission’ buses,” he said, and the agency is investigating next-generation CNG technology that could be substantially cleaner than current engines.

The Role of Hybrids
Another growing bus technology is hybrid-electric power. The Champaign-Urbana Mass Transit District (MTD) in Illinois purchased its first nine hybrid buses in 2009 and now operates 55, or 54 percent of the total fleet.

Jane Sullivan, the agency’s sustainability and transportation planner, noted that—in addition to their lower fuel usage and decreased emissions compared with traditional diesel buses—diesel-electric hybrids can easily be incorporated into an existing fleet.

“Other alternative fuel options require installation of new fueling and maintenance infrastructure that is not required for diesel-electric hybrids,” she said. “Diesel-electric hybrids made sense for MTD because we planned on a gradual change and did not want the burden of investing in new infrastructure that is only used for the new vehicles.”

Sullivan reported that the hybrid buses have helped MTD see a 25 percent reduction in fuel consumption and a decline in noise pollution by about half. In addition, she said, “Diesel-electric hybrids travel 5.5 times as many miles before they need a transmission fluid change, and 1.4 times as many miles before they need a filter change. This results in time, money, and material savings for our maintenance department.”

Amy Snyder, MTD communications specialist, described the promotional effort that went into the launch of the new vehicles. “We wanted to educate the community about the benefits of the hybrid technology, as well as getting everyone excited about the new buses,” she said. To that end, MTD wrapped the exteriors of the hybrid buses in green and yellow, distinct from the fleet’s usual blue and red “swooshes,” and distributed information about the hybrids at community events.

“Early in 2010, less than a year after the new hybrids arrived, we hired a marketing/branding firm to produce a ‘green’ promotional campaign . . . with the tagline, ‘A lot of people talk about going green. MTD’s been quietly doing it’,” Snyder said.

Another agency that operates hybrid-electric buses, King County Metro Transit in Seattle, is working closely with BAE Systems on its newest vehicles. BAE is providing its HybriDrive Series-E propulsion technology to New Flyer, which is building the buses for the agency.

Shelby Cohen, communications manager for BAE Systems, explained that this technology allows a bus to enter a stop with its engine off and to board and disembark passengers with no idling of the engine or carbon emissions. This provides both less vehicle noise and a reduction in fuel consumption.

She said: “The HybriDrive Series propulsion system uses a smaller diesel engine to spin the generator in order to produce electricity, which then is used by an electric motor to propel the bus. When the bus is headed downhill, our system produces electricity through a process called regenerative breaking; that energy is stored in a battery pack and then used when needed to propel the bus.”

Electric and Hydrogen Options
Battery-powered electric buses are another technology gaining attention among public transit agencies. VIA Metropolitan Transit, San Antonio, TX, initiated service in February 2013 with three electric buses from Proterra, funded with a $5 million grant from the federal Transit Investments for Greenhouse Gas and Energy Reduction (TIGGER) program.

The agency’s Arc service operates the electric buses on downtown circulator routes. They recharge at the Robert Thompson Transit Station at the Alamodome, receiving energy generated either by solar panels installed as part of the project or by wind farms in West Texas and on the Texas coast as part of VIA’s Windtricity agreement with CPS Energy.

In addition to the Arc service, VIA operates both CNG vehicles and hybrid buses.

In Cleveland, the Greater Cleveland Regional Transit Authority (RTA) partnered with the NASA Glenn Research Center and the Ohio Aerospace Institute to install Ohio’s first hydrogen fueling station using electrolysis.

“NASA proposed purchasing the equipment and installing it at an RTA bus garage,” said Jerome Masek, RTA publications manager. “Our role was to lease a hydrogen fuel cell bus and operate and maintain the bus and fueling equipment.”

The pilot project ended in 2013 and reported “great feedback from operators and mechanics,” Masek said. He noted that RTA had wanted to continue the project, but the company that leased the vehicle changed ownership and terminated the agency’s lease.

Public outreach surrounding the hydrogen vehicle focused on emphasizing the safety of hydrogen fuel. RTA held two public presentations showing that hydrogen is no more or less dangerous than other flammable fuels, but that it also dilutes quickly into the air in case of a leak. “After the initial push-back, RTA received only positive feedback,” Masek added.

As for the future, “We continue to research and test new products that are better for our customers and environment,” he said. “Although hydrogen was not the current solution, RTA learned an immense amount for a potential new project. As hydrogen technology continues to advance, it will allow transit authorities to provide a more sustainable solution for fueling requirements.”

Biofuels and Propane
Another increasingly popular alternative fuel is biodiesel, made from crops such as soy or corn, or from recycled cooking oil. LYNX in Orlando, FL, has seen positive environmental and other benefits since it introduced the fuel to its 280-bus fleet in 2009 as part of a “B-20” blend: 20 percent biodiesel and 80 percent traditional diesel.

LYNX Chief Executive Officer John Lewis Jr. explained that the agency not only uses biodiesel, it owns its own blending facility. “We can create custom blends, increase the ratio of biodiesel to diesel for testing,” he explained. “This also will help us if we experience a fuel disruption. It gives us flexibility in operation.”

He noted that LYNX became interested in biodiesel after former Florida Gov. Charlie Crist called for a 10 percent reduction in greenhouse gas levels in the state. “We effectively lowered carbon dioxide emissions by 26 percent in a year,” Lewis said. “In addition, LYNX became less dependent on imported fuels while supporting agricultural markets in the state.”

Lewis also said the agency reviews the benefits of biodiesel every year to make sure it remains “the right fueling source for us.”

Some public transit systems are moving in an entirely new direction, fueling their paratransit vehicles with propane. The Mass Transportation Authority (MTA) in Flint, MI, currently leads the way with 74 of the vehicles in service and another 14 expected by this summer, all powered by ROUSH CleanTech technologies.

Lynn McLean, MTA director of maintenance, vehicles, facilities, and fixed route operations, explained that trucks have used propane power since the 1970s, but the fuel was vulnerable to extremes of temperature until ROUSH developed a method of injecting the fuel directly into the cylinders (similar to the gasoline fuel injection process in cars).

“Acceptance of propane technology is like a snowball rolling downhill,” McLean said, mentioning several other transit agencies that either have added propane-powered vehicles to their fleets or plan to do so in the near future. “I think we’re going to see a lot more propane use in the transit field.” He said propane comes mostly from domestic sources, burns clean, extends engine life, and requires no special fueling facilities. Also, unlike diesel engines in paratransit vehicles, propane engines are quiet.

Another benefit to implementing propane use, according to McLean, is that the ROUSH engine has undergone testing at the Altoona Bus Research and Testing Center, making it eligible for FTA funding. In fact, he said, he leased one of MTA’s first two propane vehicles back to ROUSH for the testing process.

As part of a pilot project, the NASA Glenn Research Center purchased Ohio's first hydrogen fueling station using electrolysis and installed it at a Greater Cleveland RTA bus garage.	LYNX has used biodiesel to fuel its buses since 2009 and maintains its own blending facility.