This paper describes the operational testing of three quieted heavy-duty diesel trucks. The noise control treatments installed on the trucks included partial engine enclosures, improved exhaust systems, and 2-stage engine mounts on one of the trucks. The trucks accumulated 229,844 miles and the treatments were found to have negligible quantifiable impacts. Their operation was comparable to comparison untreated vehicles and there was no evidence of payload displacement because of the treatment weight. Predicted and observed fuel economy impacts were virtually immeasurable. Maintenance costs increased by 0.69% because of the impact of the enclosures on regular maintenance.