This document describes a test method for measuring a quantity representative of the intrinsic characteristics of sound reflection from railway noise barriers and related devices acting on airborne sound propagation, the sound reflection index and then calculate a single-number rating for sound absorption from it. The test method is intended for the following applications: determination of the intrinsic characteristics of sound absorption of noise barriers and related devices acting on airborne sound propagation to be installed along railways, to be measured either on typical installations alongside railways or on a relevant sample section; determination of the intrinsic characteristics of sound absorption of noise barriers and related devices acting on airborne sound propagation in actual use under direct sound field conditions; comparison of design specifications with actual performance data after the completion of the construction work; verification of the long term performance of noise barriers and related devices acting on airborne sound propagation (with a repeated application of the method). The test method is not intended for the following applications: determination of the intrinsic characteristics of sound reflection of noise barriers and related devices acting on airborne sound propagation to be installed in reverberant conditions, e.g. inside tunnels or deep trenches. Results for the sound reflection index are expressed as a function of frequency, in one-third octave bands, where possible, between 100 Hz and 5 kHz. If it is not possible to get valid measurements results over the whole frequency range indicated, the results are given in a restricted frequency range and the reasons of the restriction(s) are clearly reported.