Geometric Criterion for Flange Climb Derailment and IWS-Based Implementation

A recent flange climb derailment suggests that the current lateral/vertical load (L/V) ratio-based criteria may not be adequate to assess the risk of derailment in all circumstances. To better understand and prevent similar derailments, TTCI defined three friction coefficients to analyze the potential issues of the current criteria, developed a new geometric criterion to assist in derailment risk assessment, and modified the instrumented wheelset (IWS) processor to use the wheel profile to determine the wheel/rail (W/R) vertical contact position and contact angle. Analysis shows that the uncertainty of friction coefficient, and the nonmonotonicity of contact angle during the process of flange climb may lead to a misjudgment of the derailment risk based on L/V ratio-based criteria. Meanwhile, the geometric criterion can accurately assess the risk of flange climb derailment by judging whether flange climb is imminent. The W/R contact position is recommended as an index for derailment risk assessment.