The European Standard EN 13231-5 recommends intervention thresholds above which a significant increase in noise and dynamic forces are expected due to increased corrugation depth causing damage to the ballast structure (Figure 2). However, specific types of rail defects that occur at speeds above 160 km/h (e.g. belgrospi) require a lower intervention threshold to reduce the dynamic forces transmitted to the railway infrastructure. Dynamic forces depend on the unsprung mass and vehicle speed, as well as the wavelength and amplitude of the unevenness (defect) on the running surface of the railhead.