MEDIA, Pennsylvania — With a mixture of new and retrofitted vehicles, a local school district has launched a fleet of 23 school buses powered by compressed natural gas (CNG).

Rose Tree Media School District recently purchased 15 new Thomas Built CNG buses and retrofitted eight older diesel buses to run on the alternative fuel.

Last week, the district held a ribbon-cutting ceremony for the CNG buses, with district stakeholders and other dignitaries getting a chance to ride one of the green vehicles.

PHOTOS: To view a photo gallery of Rose Tree Media School District's CNG bus ceremony, go here.

Rose Tree has already put the CNG buses into service, and Superintendent James Wigo said that results so far have been favorable.

"The drivers absolutely love the buses," Wigo said, noting that one of the unexpected benefits has been the quieter engine. "The kids are not screaming over the sound of the diesel. It really changed the whole environment on the bus."

Rose Tree decided to delve into CNG buses after an analysis by Johnson Controls found that on a slow conversion schedule, the district could achieve a $1 million net benefit over a 20-year period.

"That didn't sound like a lot, but we plan to convert the fleet quicker," Wigo said, "It takes some time to make up the cost differential [of a CNG bus compared to a diesel], but the whole time we’re using clean fuel. I think that’s the key."

Cutting emissions was one of the top factors in the decision to switch to CNG.

"We probably reduce hydrocarbon spewing by 25 to 30% in the CNG buses compared to diesel buses," Wigo said.

Grant funding has helped in acquiring the alternative-fuel buses. Over the past two years, Rose Tree has received about $800,000 in grants for the project.

The district also financed construction of a fast-fill CNG fueling station and retrofits to the bus garage for servicing the new vehicles.

In addition to the 23 units that are now in service, Rose Tree may acquire 12 more for the next school year, with more to come after that. The district has a total of 74 buses, transporting students to about 100 schools and logging just over 1 million miles per school year.

"We would love to have half of our fleet converted within the next three years," Wigo said.