This document specifies a direct measurement method for characterizing the surface roughness of the rail and wheel associated with rolling noise (“acoustic roughness”), in the form of a one-third octave band spectrum. This document describes a method for: a) selecting measuring positions along a track or selecting wheels of a vehicle; b) selecting lateral positions for measurements; c) the data acquisition procedure; d) measurement data processing in order to estimate a set of one-third octave band roughness spectra; e) presentation of this estimate for comparison with limits of acoustic roughness; f) comparison with a given upper limit in terms of a one-third octave band wavelength spectrum; g) the measuring system requirements. It is applicable to the: a) compliance testing of reference track sections in relation to the acceptance test for noise emitted by railway vehicles; b) performance testing of track sections in relation to noise emitted by railway vehicles; c) acceptance of the running surface condition only in the case where the acoustic roughness is the acceptance criterion; d) assessment of the wheel surface condition as an input for the acoustic acceptance of brake blocks; e) assessment of the wheel and rail roughness as input to the calculation of combined wheel rail roughness; f) diagnosis of wheel-rail noise issues for specific tracks or wheels; g) assessment of the wheel and rail roughness as input to rolling noise modelling; h) assessment of the wheel and rail roughness as input to noise source separation methods. It is not applicable to the: a) measurement of roughness (rail roughness, wheel roughness or combined roughness) using an indirect method; b) analysis of the effect of wheel-rail interaction, such as a “contact filter”; c) approval of rail and wheel reprofiling, including rail grinding operations, except for those where the acoustic roughness is specifically the approval criterion (and not the grinding quality criteria as provided in e.g. EN 13231-3); d) characterization of track and wheel geometry except where associated with noise generation.