The National Renewable Energy Laboratory (NREL) has released an interim report on their ongoing evaluations of the Azure Dynamics Balance Hybrid parcel delivery trucks being used by FedEx in and around the Los Angeles, California area.  These trucks are gasoline hybrid electrics based on the Ford E-450 Strip Chassis, which are being compared to the standard diesel models in the same LA-area fleet, which are the Freightliner MT-45 chassis.

NREL says they will have the full analysis and comprehensive data at the end of the testing, which is due to finish at year’s end.  Data is being collected during vehicle use and includes fuel economy and costs, maintenance and operating costs, and vehicle uptime (reliability).

The interim report shows results gathered so far during live vehicle drive cycle use and also compares with a comparative hybrid and diesel-only truck at NREL’s laboratory.

The results show that the gasoline electric hybrids with the Balance Hybrid technology, in two of the three test cycles, is about equal in fuel economy to the diesel-only truck.  This is primarily due to gasoline’s lower energy content in comparison to diesel combined with the lower efficiency of spark-induced firing (spark ignition) versus the more efficient compression ignition used in diesel engines.

The NREL study is halfway done, having completed the first six months of a one year total study.  These preliminary results are not final and NREL emphasizes that after a full year, more comparable averages will be available for conclusions.

In my mind, to editorialize a bit, the conclusions from this interim report are pretty obvious: just because it says “hybrid” doesn’t make it the best choice.  I would be interested in seeing the same study done comparing a plug-in diesel electric hybrid truck technologies versus both gasoline electric hybrid and standard diesel in the same vehicle models.  It’s likely that the diesel-electric would have better economy than both competitors, especially if utilizing start-stop and regenerative braking technologies.  These delivery trucks spend a fair amount of time idling (thus start-stop being appropriate) and also stop and go often (hence regenerative braking).

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