This International Standard specifies an engineering method for measuring the noise emitted by two-wheeled mopeds in motion [as defined in ISO 383S1)I. The method is designed to meet the requirement of simplicity as far as it is consistent with reproducibility of results and realism in the operating conditions of the moped. The specifications are intended to reproduce the noise level in urban traffit flow of irregular Character, with full use of the engine power available. NOTE – The test method calls for an acoustical environment which tan only be obtained in an extensive open space. Such conditions tan usually be provided for - type approval measurements of mopeds, - measurements at the manufacturing Stage, and - measurements at off icial testing stations. lt should be noted that spot checking on the road of mopeds in use tan rarely be made in an ideal acoustical environment. If measurements have to be carried out on the road in an acoustical environment which does not fulfil the requirements stated in this International Standard, it should be recognized that the results obtained may deviate appreciably from the results obtained using the specified conditions. A method better fitted to the spot checking on road of mopeds in use will be specified in a future International Standard.