A unique experiment has been conducted to identify the dependence of variations in truck noise emission measurement data upon changes in vehicle performance and sound propagation properties. A comparison of data measured at different sites and at different times at the same site by previous investigators [e.g., J.E. Piercyet al., “Mechanisms Causing Variability in Noise Testing of Light Motor Vehicles,” NRC, Ottawa, Ontario (1976)], has shown a variability in the mean maximumA‐weighted sound pressure level of up to 4 dB. Little similar data is available for medium and heavy‐duty trucks. In this experiment, preliminary data have been obtained for one gasoline and two diesel‐fueled trucks performing SAE J366b drivebys, simulated drivebys, and idle‐maximum idle runups. The results obtained to date, as part of a one year series of tests, are presented as a function of several of the various performance and environmental variables.