When they’re cruising the trails of local woodlands and prairies, the Forest Preserve District of DuPage County’s newest sport utility vehicles won’t be much louder than a bicycle.

As part of its effort to convert its entire vehicle fleet to alternative fuel sources by 2011, the district recently purchased two new gasoline-electric hybrid Chevrolet Tahoes for the Forest Preserve police.

While the hybrid SUVs each cost about $15,000 more than the standard model, they will each save about $31,000 in fuel costs over their lifetime and cut emissions in half, said John Walton, the district’s fleet services manager.

“In 2001, the board voted a mandate that we go 100 percent alternative fuels by 2011, which is just three years away,” Walton said. “We’re about 80 percent of the way there now.”

The Tahoes join a fleet that already includes cars and trucks that run on natural gas, liquid propane, E85 ethanol and biodiesel fuels. All of these fuels produce less polluting emissions than gasoline and, despite common misconceptions, are safer to use, Walton said.

“The most dangerous fuel we us is gasoline,” he said.

Many of the fuels used in the district fleet are significantly cheaper than the $4 per gallon price of gas. The district pays about $1.04 for the natural gas equivalent of a gallon of gasoline and about $2.14 a gallon for liquid propane, Walton said.

Rich Gunther is a fleet account executive for General Motors specializing in government fleets and alternative fuels. He said the district is at the forefront of the alternative-fuel movement.

“There’s no one alternative fuel sources that’s going to get us where we need to go,” Gunther said.

Gasoline-electric hybrids will help conserve existing supplies of gasoline, and fuels like natural gas and propane are viable alternatives for large fleets like the district’s, he said.