Systems and methods in which worn railroad rails and wheels are repaired. For rail repair, a mobile additive manufacturing unit (i.e., 3D printer) operates along the rail and dispenses molten metal on the previously prepared portion of the rail. Reinforcing composite materials in powder form or pieces of composite materials may be added to the molten metal to enhance mechanical properties. For wheel repair, a fixed additive manufacturing unit is used in the same or similar manner as the mobile additive manufacturing unit for the rails albeit the wheel is rotated relative to the additive manufacturing unit. The repaired surface of the rails and wheels have dimension accuracies and surface finishes that are substantially the same as the original rails and wheels with the same or better mechanical strength and hardness as the original after resurfacing with grinding or milling tools.