A new study released from the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) evaluated gasoline hybrid electric delivery vehicles in comparison with conventional diesel vehicles on performance, emissions and fuel economy measures. Conventional gasoline engines are less efficient than conventional diesel engines, so in the past, many fleet operators preferred diesel powered trucks. However, with growing innovation in hybrid electric technology, the status of diesel as the cleanest and most efficient option is being re-evaluated.

“We conducted this study to show how a gasoline hybrid might perform compared to a conventional diesel truck given that gasoline engines are less efficient than diesel engines and generally not used in heavier vehicles,” said Lee Slezak, program manager for DOE’s Advanced Vehicle Testing Activity.

The evaluation results demonstrate that gasoline hybrid electric vehicles (gHEVs) are an increasingly viable alternative to conventional diesel trucks. While gHEVs were comparable to diesel trucks in terms of fuel cost per mile and maintenance cost per mile, the gHEV group had significantly better fuel economy and decreased tailpipe emissions.

NREL’s Fleet Test and Evaluation Team conducted the study on FedEx Express parcel delivery routes in the Sacramento and Los Angeles areas. Three newly deployed FedEx Express gHEVs were compared with three conventional diesel trucks used as a control group. The 12-month study collected data on fuel economy and emissions using chassis dynamometer testing, and maintenance and fuel costs were recorded for each vehicle.

FedEx Express

FedEx Express is just one fleet operator integrating gasoline hybrid electric vehicles into their conventionally diesel-powered fleets. A study by NREL shows that gHEVs have lower emissions and better fuel economy than conventional diesel vehicles. Credit: FedEx Express

The gHEV trucks produced substantially fewer tailpipe emissions in all driving scenarios tested in the laboratory when compared to conventional diesel delivery vehicles. In addition, the gHEV trucks performed with a 20 percent fuel economy improvement on a drive cycle representing routes with frequent stops and accelerations. On drive cycles representing routes with fewer stops and accelerations, the gHEV and conventional diesel trucks performed comparably.

FedEx Express recently added 20 gHEVs for parcel delivery routes in Los Angeles and Sacramento, Calif. The gHEVs experienced a smooth integration and deployment into commercial service. During the study period, the gHEVs performed as expected, experienced a minimum of unscheduled maintenance and met the expectations of FedEx Express.

“Southern California continues to experience the worst air quality in the nation, and transitioning heavy-duty vehicle fleets to cleaner-burning vehicle technology is an important element of our overall clean air goals,” said Barry R. Wallerstein, executive officer of the South Coast Air Quality Management District.

FedEx Express also operates a larger hybrid fleet that has driven more than 8 million miles since the beginning of the program. In Bronx, N.Y., FedEx Express operates an all-hybrid station and nearly half of the vehicles are gHEVs.

The funding for this study was provided by DOE’s Vehicle Technologies Program with additional funding from CALSTART and the South Coast Air Quality Management District.

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