This part of ISO 13472 specifies a test method for measuring in situ the sound absorption coefficient of road surfaces for the one-third-octave-band frequencies ranging from 250 Hz to 1 600 Hz under normal incidence conditions. For special purposes, the frequency range can be changed by modifying the dimensions of the system. The test method is intended for: a) determination of the sound absorption coefficient of semi-dense to dense road surfaces (and, if of interest, also the complex acoustical impedance); b) determination of the sound absorption properties of test tracks in accordance with standards such as ISO 10844 and test surfaces defined in national and international type approval regulations for road vehicles and vehicle tyres; c) verification of the compliance of the sound absorption coefficient of a road surface with design specifications or other requirements.