An indepth study to reduce noise produced by a typical highway diesel truck is being conducted to determine levels and costs attainable by practical means. Truck noise reduction involves isolating several individual noise sources, that is, fan, exhaust, engine-radiated, intake system, and others, and developing means to reduce each. Tire noise and major engine revisions are not considered in this project. Goals of 78 dB(A) (per SAE J366a) without engine enclosure and 75 dB(A) with engine enclosure are believed possible on the vehicle configuration being studied. This project is sponsored by the U.S. Department of Transportation Office of Noise Abatement, and industry.