Reexamination of the Evaluation Criteria for Running Safety Against Flange-Climb Derailment in Modified-Arc Wheel Treads

This study reexamines the evaluation criteria for running safety against flange-climb derailment in railway vehicles, which have traditionally relied on empirical standards established more than half a century ago in Japan. Although the existing evaluation procedure remains effective, its limit value was derived from previous-generation vehicle designs and operational conditions. Focusing on the derailment quotient, a key indicator of running safety, this research investigates an appropriate limit value for modern wheel profiles through both theoretical and probabilistic analyses. Using Nadal’s criterion and vehicle dynamics simulations, the study compares the basic tread and modified-arc wheel tread profiles. The results show that the modified-arc wheel tread provides a greater safety margin than the conventional basic tread and that an equivalent safety level can be achieved when the limit value is set to approximately 0.97 instead of the current 0.95. These findings suggest that applying a uniform safety factor is insufficient, highlighting the importance of a context- specific approach for reliable derailment risk evaluation.