Clean Air Technologies

Biodiesel
This relatively new type of alternative fuel is processed from any vegetable oil—including used oil from fast-food restaurants—and can power most diesel-engine vehicles without modification. Sales of biodiesel are gradually increasing—75 million gallons were sold in the U.S. in 2005—and many government vehicles like these from the USDA use it to fill up. Though it burns 78 percent cleaner than petroleum diesel and comes from a renewable source, it is double the cost and fueling stations are scattered. Furthermore, only a fraction of vehicles in the U.S. have diesel engines, though new fuel-efficient models on the market have recently gained in popularity.