Chuck Loeffelholz's been driving diesel trucks for 25 years. He knows the smell and the color of diesel, but he recently learned that he's been filling up his truck with a new biodiesel fuel.

"The truck runs fine. If they never would have told me the day they put it in, I would have never known," Loeffelholz said.

Loeffelholz started pumping 80-percent ultra-low sulfur and 20 percent soybean-based biodiesel into the tank last week. The new mix is going into more than 100 UW vehicles, such as dump trucks and snowplows.

"We've been looking for ways to clean up our emissions as much as possible," said Rob Kennedy, senior transportation planner for the UW.

The mix will reduce emissions by 15 percent. Ultra-low sulfur reduces soot and biodiesel is a clean-burning, renewable fuel alternative. But there are some drawbacks.

Kennedy says there is a 10-percent loss in mileage, and the university will have to pay $20,000 more for a total of $70,000 a year on fuel.

"It's not a cost-saving thing, at least in the short term its costing us 40 cents more a gallon," Kennedy said.

"The benefit is less air pollution that we'll be breathing in, and using the soy-blend -- it's a renewable fuel and that's good for farmers," said Erin Roth, executive director of the Wisconsin Petroleum Council.

This special mix won't be sold at the pump, it's still being tested. But the ultra-low sulfur diesel fuel will be in the mix by July 2006.

"This, in my mind, will be the hugest environmental benefit in terms of air quality that we've seen in this country since the 1990s' Clean Air Act Amendments," Roth said.

Madison Metro will be using the new ultra-low sulfur fuel by the summer, joining cities such as Chicago and Minneapolis. Minnesota passed a state law mandating every gallon of diesel sold in the state have 2 percent of the ultra-low sulfur fuel by July of this year -- one year before the federal regulations kick in.

Read More: UW-MADISON FILLS UP ON LESS-POLLUTING BIODIESEL MIX