Hybrid buses operate with lower emissions, greater fuel efficiency

A recently released study by the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) concludes that hybrid buses operate with lower emissions and greater fuel efficiency than conventional diesel buses.

The year long evaluation of 10 prototype diesel hybrid-electric buses in the Metropolitan Transportation Authority’s New York City Transit (NYCT) fleet of 4,489 buses showed that these hybrid buses have a 10 percent higher in-service fuel economy. According to chassis dynamometer emissions testing, the hybrid buses had 36 percent lower oxides of nitrogen and 50 percent lower particulate matter emissions than diesel buses on a central business district cycle.

“Taking the state of the technology into consideration, we think hybrid-electric buses are going to make a very positive impact on our fleet,” said Bill Parsley, NYCT’s director of research and development. NYCT has awarded contracts for an additional 125 hybrid buses in 2002 and 200 hybrid buses in 2003.

The NREL report, NYCT Diesel Hybrid-Electric Buses: Final Results, summarizes the work completed during the yearlong Transit Bus Evaluation Project to collect fueling, maintenance, performance and emission data from NYCT.

While the hybrid buses have greater fuel economy than diesel buses, maintenance costs were significantly higher due in part to the maturity level of the hybrid propulsion system. These costs are expected to drop as the technology advances.

The evaluation was funded by DOE’s Office of Heavy Vehicle Technologies and Office of Technology Utilization’s Field Operations Program and managed by NREL. It began after NYCT purchased the prototype diesel hybrid-electric buses from Orion Bus Industries with BAE SYSTEMS’ HybriDriveTM propulsion system after the success of an early prototype hybrid bus project.

The final results report and two additional reports related to this Transit Bus Evaluation Project, NYCT Diesel Hybrid-Electric Buses: Program Status Update and NYCT Diesel Hybrid-Electric Buses: Final Data Report, are available through NREL’s Alternative Fuels Data Center, http://www.afdc.doe.gov or 1-800-423-1DOE.