Top-of-rail friction control for curve noise mitigation and corrugation rate reduction

Top-of-rail friction modifiers are designed to control frictional characteristics at the wheel–rail interface that influence noise, corrugations, and lateral forces. Key characteristics of the resulting thin film are: (1) controlled intermediate coefficient of friction and (2) positive friction, to reduce roll–slip oscillations related to both curve squeal noise and short pitch corrugation development. Practical results are presented on the effect of friction modifiers on curve squeal and flanging noise generation at a range of European mass transit sites. Reductions in A-weighted noise ranging from 6.3 to 22.8 dB were recorded, with an average reduction across the different test sites of 12 dB. Both top-of-rail squeal and flanging components of noise were reduced.The effect of friction modifier on short pitch corrugation development was evaluated over several years at two curves at Metro Bilbao. Under conditions where corrugations grew from 0.1 to 0.5 mm in 18 months under baseline conditions, with application of friction modifier essentially no corrugation growth occurred in an equivalent time period.