The effect of normal load, contact velocity, and dwell time on the coefficient of adhesion at slip in braking was investigated. A test rig that simulated locomotive wheel/rail interactions was used for the experimentation. The results indicated a drop in the coefficient of adhesion with increasing speed. However, normal load, contact velocity, and dwell time, as operating variables, did not have any effect on the variation of the coefficient of adhesion. A description of the investigation and recommendations for further studies is included. / Master of Science