AbstractIn an earlier paper, allowable bending fatigue stress was expressed in terms of ultimate tensile strength. For many reasons, it is useful to express allowable bending fatigue stress in terms of hardness. Hardness is occasionally used to obtain a quick approximation of tensile strength. The rail grades are named by hardness because they are directly related to the wear properties. Many metal alloys are heat treatable, and the hardness, rather than the tensile strength, is known. In this technical note, the allowable bending fatigue stress is expressed in terms of hardness. The applicability of the derived relation on American Railway Engineering and Maintenance-of-Way Association steel, welded rail joints, and head-hardened rail sections is discussed, which has implications in rail-section design. This note provides an addition and supplement to the earlier paper.