The research described in this report was undertaken to evaluate the potential contribution to the overall annoyance of heavy truck noise of the impulsive character of exhaust noise created by engine compression-release braking devices. Although growing numbers of trucks are likely to be equipped with these safety devices in the future, current methods for assessing health and welfare effects of traffic noise on residential populations make on specific provision for annoyance associated with impulsive noise sources. The two major goals of the current research were (1) to quantify the impulsive emissions generated by compression-release engine brakes in the course of typical operation of heavy vehicles so equipped, and (2) to quantify the annoyance associated with such emissions. A program of physical field measurements designed to meet the first goal is described in Section III of this report. Subjective judgment experimentation conducted under laboratory conditions to meet the second goal is reported in Section IV.