The effect of noise on communities surrounding major roads presents a serious problem. Procedures have been developed to estimate the magnitude and the extent of the noise generated from vehicles operating on roads. Until recently calculation of road traffic noise levels have neglected the impact of weather conditions. Procedures have only considered situations in which the atmosphere was homogeneous and sound waves travelled in straight lines. This paper describes a new method for calculating road noise, taking into consideration the effect of weather factors, such as wind and temperature. Using this new method, which is compulsory in France for the study of road projects, will enable us
to make a better evaluation of the impact of noise from major roads.