|The study found the hybrids delivered 27% better fuel economy than the conventional diesels. Click to enlarge.|
The National Renewable Laboratory has recently published its final report on the GM-Allison hybrid electric buses in service at King County Metro (KCM) Transit in King County, WA. The report includes 12 months of performance data—April 2005 through March 2006—on ten 60-ft New Flyer buses using the two-mode hybrid powertrain. (Earlier post.)
The study, which focuses on a comparison of diesel buses operating from KCM’s Ryerson Base and hybrid buses operating from Atlantic Base because of their similar duty cycles, found that the hybrid buses from Atlantic Base had a 27% higher fuel economy on average compared with that of diesel buses at Ryerson Base.
Over the 12-month period, the diesel buses also carried a 4.5% higher maintenance cost than the hybrids: $0.46 per mile for the diesels, compared to $0.44 per mile for the hybrids.
Combining fuel costs with maintenance costs, an evaluation of total cost per mile gave the hybrids a distinct operational economic advantage: $1.06 per mile compared to the diesel $1.25 per mile.
|Results of laboratory emissions testing using four different test cycles. Click to enlarge.|
The NREL team performed emission testing on one hybrid bus (of the 235) and one conventional bus (of the 30) during May-June 2005 using four driving cycles: Central Business District (CBD), Orange County (OCTA), Manhattan, and a custom test cycle developed from in-use data on the King County Metro (KCM) fleet’s operation.
To evaluate the effects of additional engine and vehicle loading due to grade, select cycles were repeated with and without this added load.
Detailed results of this testing—which show a marked benefits to the hybrids except in one test combination (PM, KCM cycle)—are published in a separate report, King County Metro Transit: Allison Hybrid Electric Transit Bus Laboratory Testing.
King County Metro Transit Hybrid Articulated Buses: Final Evaluation Results (NREL/TP-540-40585)