Interlaboratory Cross-Check of Heavy-Duty Vehicle Chassis Dynamometers

Six laboratories capable of chassis-testing heavy-duty vehicles participated in a crosscheck program designed to compare emissions results from a Ford L-9000. The single-axle vehicle was shipped to each laboratory and tested through a series of UDDS and steady-state cycles. The resulting data were compared statistically using reproducibility and repeatability analyses. Although one lab produced some results that significantly differed from the other five, the remaining labs produced comparable results. TPM, CO and THC were the most variable while NO_X and CO₂ were most stable. Lab differences included atmospheric and environmental conditions, road-load curve application and drivers. Comparison of steady state and transient tests suggest that driver variability is not a major factor.