Effect of traffic mix volume and speed on highway noise levels

Since Johnson and Saunders [“The Evaluation of Noise from Freely Flowing Traffic,” J. Sound Vib. 7, 287–309 (1968)] derived an expression relating the median traffic noise level as a function of traffic flow characteristics, many other relationships have emerged. These relationships have been used to design nomographs and computer noise prediction programs. This paper discusses the various basic formulation equations used to relate traffic mix and speed to the noise levels from motor vehicles. Parametric analysis of the basic equations used in the Revised Design Guide (NCHRP Report 3-7/3) for automobiles, medium trucks and heavy trucks, is performed. The effects of variations of traffic mix volume and speed on “equivalent” noise level at receivers are illustrated. Figures are plotted so that the results can be used to find the minimum noise levels for a given speed, based on a given traffic mix.