In less than two weeks, Kings Park public school students will be shepherded to school in yellow buses with a heavy dose of green.

The district purchased four new propane school buses this year. The decision to begin transitioning to propane vehicles was a "no-brainer," Superintendent Timothy T. Eagen said in an interview Thursday. The buses arrived last week.

"It's a quieter, cleaner, more cost-efficient vehicle," Eagen added. "Propane is like your backyard grill; it burns clean, there's no odor."

Propane offers better mileage and at a cheaper cost than diesel, the fuel school buses typically run on, Eagen said. Diesel buses cost about $100,000; propane models cost an additional $10,000, though fuel savings quickly compensate, Eagen said.

Kings Park is the only school district in Smithtown that owns its fleet of buses. The district joins several others on Long Island that have also made the switch, among them Roslyn, Northport and Riverhead.

Roslyn began purchasing propane buses in the past five years and was the first Nassau County district to do so, transportation supervisor David Shoop said yesterday. Roslyn now has more than a dozen propane school vans.

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In 2012, Riverhead became the first district on Long Island to purchase a propane bus, transportation director Amala Cain said Thursday. It now has a "couple of dozen" propane vehicles and is slowly converting to an all-propane fleet, she added.

Riverhead served as the model for the Kings Park and Northport school districts. Officials in both districts visited Riverhead's fleet of 65 buses -- which include diesel and propane -- before buying their own propane vehicles.

Officials in Kings Park, which has 60 buses, said it could take the district more than a decade to phase out its diesel buses. The district may be ahead of the curve, but Eagen thinks there is a broader shift underway.

"My general sense is that more districts may look to do what we are doing, which is begin replacing their fleet with propane buses, and slowly transition," he said.