This part of ISO 13472 describes a test method for measuring in situ the sound absorption coefficient of road surfaces as a function of frequency in the range from 250 Hz to 4 kHz. Normal incidence is assumed. However, the test method can be applied at oblique incidence although with some limitations (see annex F). The test method is intended for the following applications: — determination of the sound absorption properties of test tracks according to ISO 10844, with limitations, and other similar standards; — determination of the sound absorption properties of road surfaces in actual use; — comparison of sound absorption design specifications of road surfaces with actual performance data of the surface after completion of the construction work. The complex reflection factor can also be determined by this method.