A methodology for substantiating the optimal parameters settings of diesel generators of diesel locomotives according to the criterion of the maximum weighted average efficiency of a diesel locomotive depending on their operating conditions is presented, as well as a methodology and numerical algorithm for assessing the optimal diesel power and efficiency of diesel locomotives with electric transmission and their traction electrical machines. When choosing the optimal mode for controlling the movement of a freight train, the author recommends using the principle of parametric (additive) optimization of the transportation work of locomotives and the value of the highest efficiency of the power circuit, depending on the accepted range of changes in the speed movement of the train on the calculated section of the railway. The research results were obtained in the form of tabular data (regime card) and corresponding analytical expressions - equations for determining the parameters under study. It is recommended to test the obtained research results in real operating conditions, and continue these studies for other types of diesel locomotives and sections of the Uzbek railways of varying degrees of difficulty.