Dozens of YMCA summer campers filed out of a yellow school bus outside the Minnesota Science Museum in St. Paul, preparing for a day of learning about the environment.

The students didn’t realize their school bus was a science project in itself, part of a nine-year effort to reduce school bus pollution.

On Thursday, the Environmental Initiative celebrated the completion of Project Green Fleet, which provided fuel-efficient engines for more than 4,600 diesel vehicles across the state, including 3,200 school buses used by about 200,000 students.

The result was the equivalent of removing 750,000 cars from the road.

“We’re one of the first states to say that, and to do it in a voluntary way,” said Mike Harley, executive director of the Minneapolis-based nonprofit.

The Environmental Initiative’s partnership with the Minnesota Pollution Control Agency has provided cleaner engines for every eligible school bus in the state (some buses were too old for retrofitting, while newer ones did not require it). The state contributed $2.4 million to the effort, and a recent $1 million grant from founding sponsor Flint Hills Resources meant the project came at almost no financial cost for each school district.

Thursday’s celebration didn’t mark the end of Project Green Fleet. Next up: reducing diesel emissions for at least 100 construction vehicles in the state.

The process, which requires actually removing and replacing old engines, costs $60,000 to $80,000 for each construction vehicle. Project Green Fleet hopes to pay for about half the cost of the retrofitting, and the rest would be paid by construction companies. An industry spokesman said that participating in the project requires industry players to invest a great deal of time and money.

“They have to take equipment out of service,” said David Semerad, CEO of Associated General Contractors of Minnesota. “Sometimes, that’s not easy.”

But repowering engines could extend the life of engines and lower the amount of fuel needed to power them, and that could mean substantial savings for construction companies, Semerad said. And the environmental impact of retrofitting 100 construction diesel vehicles could exceed the gains that come from 3,200 retrofitted school buses.

The group has already worked on 46 construction vehicles, and several companies are participating, including KGM, Ames Construction Inc. and Xcel Energy. The next hurdle for the Environmental Initiative will be raising the money necessary to complete the project, an estimated $8 million, over the next five years.

Taking early action

The new initiative comes as the U.S. Environmental Protection Agency prepares to propose new, potentially more stringent pollution standards at the end of the year. Although the state is currently compliant with maximum pollution levels, it would be dangerously close to exceeding some of the lower limits that are being considered, said John Stine, commissioner of the Minnesota Pollution Control Agency.

Violating these standards could cost Minnesota $140 million to $240 million annually, and could lead to tightened restrictions for businesses seeking environmental permits.

“It’s early action,” Stine said. “It’s done before we have a club beating us over the head.”

Reducing diesel emissions — which account for more than half of air pollution generated by vehicles — also provides health benefits for Minnesotans. More than 400,000 Americans suffer from respiratory problems associated with diesel pollution, according to the Environmental Initiative.

“It makes sense for the health of our kids,” Harley said. “It makes sense for the health of our drivers.”

A group of elementary and middle school students from St. Cloud walked off the bus for the YMCA summer camp field trip to the Science Museum. One of the campers, 10-year old Holland, said she was glad to hear her school bus was eco-friendly.

“Then we know we’re not making everything worse,” she said.