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The National Renewable Energy Laboratory has completed testing of diesel and biodiesel on nine buses in a Boulder, Colorado project. The buses each racked up over 100,000 miles along the 16-mile "Skip" route in the city. Five buses ran on B20, the other four on standard petroleum diesel. NREL used standard 2000 model year Orion V buses with Cummins ISM engines that got about 4.41 mpg on the route using either diesel or biodiesel (laboratory testing had suggested a two percent drop in fuel economy using biodiesel). The buses were tested between August 2004 and July 2006.

The major negative for the biofuel was a higher per-mile average maintenance cost (seven cents vs. five cents), but "engine and fuel system maintenance costs varied widely from bus-to-bus so the $0.02 per mile average difference between the two groups is not statistically significant," Some of the cost comes from road calls where the fuel filter needed to be replaced, and the delay in service is "significant to the transit district," NREL's report says. On the plus side for biodiesel, there were lower soot levels in the B20 buses and lab testing shows "reductions in all measured pollutants, including a reduction in nitrogen oxides."

You can download the full 14-page report in PDF here.

[Source: National Renewable Energy Laboratory via Imperium Renewables]