Athens-Clarke County bus drivers couldn't.

In June, Athens Transit Director Butch McDuffie began filling up county buses, vans and service trucks with a 20 percent biodiesel mixture but didn't tell anyone to avoid any preconceived notions about the fuel. The drivers never noticed, and McDuffie declared the experiment a success.

Although they haven't caught on with the general public, the cheaper price and lower emissions of diesel fuels made from fat, grease or corn-based ethanol are making them increasingly popular with governments.

"It's going to come in the future," McDuffie said. "I think everyone's going to change over to this."

Since diesel engines don't need to be modified to run on biofuel, the switchover cost less than $10,000 for some routine maintenance work like replacing filters and cleaning fuel lines to get ready for the change, McDuffie said. And a gallon of B20 fuel is 20 cents cheaper than regular diesel, so taxpayers are saving almost $50,000 on the 22,000 to 24,000 gallons Athens Transit consumes in a month.