The transit agency in South Bend, Ind., like many others, is getting rid of its diesel-powered buses and replacing them with vehicles that run on natural gas.

The South Bend Public Transportation Corporation, known locally as “Transpo,” put in an order for 16 new coaches that run on compressed natural gas. They typically cost about $20,000 more than similar, diesel-powered vehicles, but they pay for themselves quickly, said David Cangany, Transpo’s general manager.

Transpo is paying $3.04 a gallon for diesel this year, but an equivalent amount of natural gas only costs about $1, Cangany said. Even after taking account the fact that buses burn more natural gas than diesel, the change will eventually save Transpo at least half of its $1.2 million annual fuel budget.

“It’s being green, and it’s being conscious of how we’re spending taxpayer dollars. At the end of the day, it’s good for our community,” Cangany said.

Transit agencies around the country are increasing their use of alternative fuels. The American Public Transportation Association (APTA), in an Earth Day release, reports that last year more than 40 percent of transit buses used alternative fuels.

One in five transit buses runs on natural gas. Another 13 percent are hybrid-electric and 7 percent run on biodiesel, according to APTA.

The 40 percent of buses using alternative energy compares with 3.4 percent for automobiles (including flex-fuel vehicles). Even more buses are likely to use alternative fuels in the future.

“This is good for the environment, good for the economy and good for the country,” said APTA President and CEO Michael Melaniphy, noting that much of the alternative fuels being used are produced domestically.

The environmental benefits of using alternative fuels is a matter of great debate. The industry group Natural Gas Vehicles for America, for example, claims that new natural gas vehicles can emit as much as 21 percent less greenhouse gases than new diesel vehicles. The reductions are even greater when replacing older diesel vehicles. But a study published earlier this year in the journal Science concluded that those savings were negated by methane leaks elsewhere in natural gas transmission networks.

The first transit agencies to use alternative fuel vehicles generally did so out of concerns for the environment, Melaniphy said, but more agencies are making the switch now that the technology is cheaper, smaller, safer and easier to use. These days, the appeal of alternative fuels still varies from agency to agency.

“One of the biggest appeals of transit is for people to go green. Taking public transit is an easy way to reduce your carbon footprint. We want to advance that,” said Anna Chen, a spokesperson for Metro, the transportation agency in Los Angeles County.

Los Angeles retired its last diesel bus in 2011, following nearly two decades of replacing diesel buses with “clean” vehicles. The agency, which has more than 2,200 buses, said the shift will reduce smog and greenhouse gases in the region. It also bought 25 electric buses, which are expected to arrive by the end of the year, in an effort to further lower emissions.

But Tony Bryant, director of bus maintenance for MARTA in the Atlanta region, said cost was the driving factor in the shift there. MARTA also began replacing its diesel vehicles in the mid-1990s, but it put the move on hold after 70 percent of the fleet ran on compressed natural gas.

Last year, though, MARTA decided it would start to complete the process. Buses that run on natural gas are more expensive to buy and more expensive to maintain than diesel buses, but those extra costs pale in comparison to the money MARTA would save on fuel by converting its remaining vehicles to natural gas.

“Because our fuel costs are going to decline over time, it allows us to put that money back into increased service. We can actually offer more service than we were able to before,” Bryant said.

The huge surge in U.S. production of natural gas means transit agencies can count on natural gas being cheaper for a long time, even if natural gas prices climb, Bryant said. “The fuel supply has been so plentiful that the cost of the fuel has plummeted. There is no reason to expect that to change anytime soon.”

Because natural gas is so cheap, the Atlanta agency also hopes it can convert its fleet of 400 support vehicles, along with its smaller paratransit buses to natural gas, he added.

But Bryant said the budget reasons, not environmental goals, made natural gas the clear choice for MARTA. The U.S. Environmental Protection Agency has tightened emissions standards for diesel vehicles over the last decade, so that new diesel buses and new compressed natural gas buses have “virtually identical” emissions of greenhouse gases, he said.

In South Bend, the shift to natural gas buses is part of an agency-wide focus on better environmental practices. Transpo opened a new building in 2010 that recycles water, uses geothermal energy for heating and cooling and uses intelligent lighting to save energy.

The transit agency also partnered with city hall to build a fueling station for natural gas vehicles. The city started by buying four garbage trucks that run on compressed natural gas and wants to convert 65 percent of its fleet to the new fuel. That move would save the city 22 percent of its fuel costs over five years, said Kara Kelly, South Bend’s director of communications.

Cangany, Transpo’s general manager, said the switch in fuels will also help the agency weather budget crises.

“As our funding continues to dwindle and be in question, we have to look at ways to be sustainable on our own,” he said. “It’s one of the ways we are able to be sustainable financially but sustainable environmentally.”

This story was originally published by Governing