They're still yellow, but they're also a bit more green. With the help of MassCleanDiesel, 31 Wareham school buses are undergoing exhaust system upgrades to reduce the pollution they emit.

"Cleaner buses mean a healthier environment for kids and drivers," said Ana Miranda, Wareham Public Schools Director of Operations/Finance.

Sponsored by the Massachusetts Department of Environmental Protection (MassDEP), the MassCleanDiesel program helps school bus owners add "diesel retrofits," enhanced exhaust filtering systems, to buses with engines manufactured before 2007, according to MassDEP documentation. The retrofits reduce pollution emitted from the tailpipes of the vehicles.

The upgrades, which cost approximately $1,600 per bus, are funded through federal and state grants and completed without cost to the school district, Miranda said.

"It always makes you happy when you know you don't have to spend," Miranda said. "It's a great program."

Retrofitting the older buses is not currently required by the state.  But it may be in the future, so all eligible buses are getting the upgrades.

"As long as it's a bus worth keeping, we're having them retrofitted," Miranda said. She applied for the program in 2008, and after receiving notification from the state, upgrades began last month.

Two buses at a time are sent to a vendor to have the retrofitting completed, Miranda said. It may take through the summer for all upgrades to be completed.

The district will have to ensure that when it purchases used buses in the future, that it is purchasing vehicles that have already been retrofitted or that do not need it, so the district does not have to pick up the cost of the upgrades should retrofitting eventually be required by the state, Miranda said. The two new buses purchased this spring are newer and do not require retrofitting.

The exhaust system upgrades are in addition to steps the district already takes in reducing emissions, such as requiring that drivers do not let the buses idle when picking up students, Miranda said. And the upgrades are an "important step in reducing the amount of greenhouse gases in the environment overall."