This European Standard describes a test method for measuring a quantity representative of the intrinsic characteristics of sound reflection from road noise reducing devices: the reflection index. The test method is intended for the following applications: — determination of the intrinsic characteristics of sound reflection of noise reducing devices to be installed along roads, to be measured either on typical installations alongside roads or on a relevant sample section; — determination of the in situ intrinsic characteristics of sound reflection of noise reducing devices in actual use; — comparison of design specifications with actual performance data after the completion of the construction work; — verification of the long term performance of noise reducing devices (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 reducing devices to be installed in reverberant conditions, e.g. inside tunnels or deep trenches. Results are expressed as a function of frequency, in one-third octave bands between 100 Hz and 5 kHz. If it is not possible to get valid measurements results over the whole frequency range indicated, the results should be given in a restricted frequency range and the reasons of the restriction(s) should be clearly reported.