Keywords: wheel–rail interaction, curved track dynamics, stochastic track irregularities, transition curves, derailment risk, multibody dynamics.

This study investigates asymmetric wheel–rail interaction and derailment risk in curved railway tracks incorporating transition geometry and measured track irregularities. An integrated multibody dynamic model based on the European Railway Research Institute (ERRI) formulation is implemented in VI-Rail to simulate realistic wheel–rail contact behaviour, suspension dynamics, and vehicle–track interaction under varying curve radii, vehicle speeds, and irregularity conditions. The derailment coefficient lateral-to-vertical force ratio (L/V) exhibits a progressive increase within the transition region owing to the gradual introduction of curvature and cant, reaching its peak at the onset of the circular track. Thereafter, the force response tends toward a quasi-steady oscillatory behaviour in the curved section, suggesting a stabilized wheel–rail interaction under constant curvature conditions. A non-monotonic speed dependence is observed, with L/V decreasing from approximately 0.58 at 40 km/h to 0.49 at 100–120 km/h, followed by an increase to nearly 0.55 at 140 km/h. Curve radius strongly influences derailment behaviour, where sharp curves (R = 250 m) produce significantly higher L/V values, while larger radii (R = 500 m) maintain comparatively stable operation. Under severe operating conditions, pronounced L/V spikes and near-zero vertical wheel loads indicate elevated derailment susceptibility and intermittent wheel–rail contact loss. The findings highlight the coupled infl uence of speed, track geometry, and PSD-based track irregularities on vehicle stability, emphasizing the importance of asymmetric wheel–rail interaction in derailment assessment and safer railway track design.

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