A new approach of assessing rail roughness

Rail roughness with a broad spectrum of wavelengths is always present on the running surfaces of the rails. It has been shown that there is a high dependence between the amplitude and the wavelength of the roughness. Further, the magnitude and frequency of the vertical wheel-rail contact force is depending on the amplitude and wavelength of the roughness. The standards used for monitoring roughness all use constant values as thresholds in large wavebands, see for example the coming EU standard prEN 1321-3 that controls the condition after grinding. However, in the ISO standard ISO EN 3095 the track quality has to satisfy a rail roughness limit that is based on one-third octave bands. The standard is used when measuring noise levels from railbound vehicles ensuring a minimal spread in noise level between different tracks. A new approach to present rail roughness has been implemented at the Swedish Railway Administration, Banverket. It is based on a transformation of the measured longitudinal rail profile to a one-third octave band spectrum, and a weighting of the spectrum against the limit described in ISO 3095. The result is presented as a spectrogram. By applying spectrograms on the results received, the rail roughness can be presented with both spatial and wavelength resolutions. This gives a good overview of the track quality. A handbook has been written on how to interpret the spectrograms. In the handbook, a threshold is given to assess the need for grinding.