Bioethanol can be blended with many other fuels as an oxygenate, the idea being, I guess, to improve combustion and fuel efficiency. With diesel it can lower the temperature it starts to solidify which could be useful in winter months.
According to the Green Car Congress website
O2Diesel Corporation, a provider of ethanol-blended diesel fuels (e-diesel) for centrally fueled fleets, has entered into an agreement with Ben Franklin Transit (BFT) in Richland, Washington, to begin testing a blend of its O2Diesel e-diesel in combination with a B20 biodiesel blend in 20 transit buses