1.1 This European Standard specifies a direct method for characterizing the surface roughness of the rail associated with rolling noise ("acoustic roughness"), in the form of a one-third octave band spectrum. This standard describes a method for: a) selecting measuring positions; b) data acquisition; c) measurement data processing in order to estimate a set of one-third octave band roughness spectra; d) presentation of this estimate for comparison with limits of acoustic roughness; e) comparison with a given upper limit in terms of a one-third octave band wavelength spectrum. 1.2 It is applicable to the: a) performance testing of reference track sections for the measurement, within a period of three months before or after roughness characterization, of noise emitted by railway vehicles for acceptance testing purposes; b) acceptance of the rail surface condition only in the case where the result of the direct measurement of the acoustic roughness is regarded as an established acceptance criterion.