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: selecting measuring positions; data acquisition; measurement data processing in order to estimate a set of one-third octave band roughness spectra; presentation of this estimate for comparison with limits of acoustic roughness; comparison with a given upper limit in terms of a one-third octave band wavelength spectrum. It is applicable to: 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; the 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. It is not applicable: to the measurement of rail roughness using an indirect method; to the measurement of combined wheel-rail roughness; to the analysis of the effect of wheel-rail interaction, such as a "contact filter"; to the approval of rail reprofiling, including rail grinding operations, except for those where the acoustic roughness (and not the level of corrugation) is an established approval criterion; to the characterization of track geometry. Testing and approval of measuring apparatus are not part of the scope of this standard.