Wheel-rail adhesion has been the subject of vital interest to locomotive builders and the railroad. This area continued to receive considerable attention during the past decade due to the significant increase in horsepower available for traction of internally powered locomotives. For background information, this publication will briefly review the factors that affect adhesion and some of the published data on available adhesion between locomotive wheels and rail as a function of speed. Instrumentation, testing procedure, and results of adhesion tests on an SD-45 locmotive are discussed, and developed adhesion versus speed curves for different operating conditions are presented.