This report presents the three-phase program to design, fabricate, test, and demonstrate economical and practical methods of reducing noise levels on underground coal mining portal buses (mantrip vehicles). The noise-control treatments applied to a production- model portal bus were as follows: (1) wheel-rail vibrations were isolated from the vehicle frame by inserting elastomeric materials between suspension components. (2) Vibration-induced noise was reduced by replacing all large sheet metal panels, except floor plates, with damped steel panels. (3) Motor noise was reduced by tight-fitting covers made from damped steel and lined with sound- absorbing material and elastomeric motor mounts. (4) The standard spur gears used in the traction drive system were replaced with helical gearsets. The program reduced the average sound level to below 85 dba for typical operating conditions.