A statistical theory for road traffic noise based on the composition of component response waves and its experimental confirmation

None of the existing standards, which express the needs of engineers, consider correlation properties of traffic noise. But the correlation properties of traffic noise often seem to have a fundamental importance in certain engineering fields of noise control, such as the design of barriers for sound insulation and the detection of voices in noisy out-of-doors situations. In this paper, firstly, the correlation properties in the time domain and the frequency characteristics of the sound intensity at an observation point are discussed in the general case: i.e., for arbitrary values of quantities such as the propagation characteristics of the traffic sound energy, the numbers of lanes of road and of types of vehicles, the mixture ratios of vehicle types, the average number and respective acoustic power distributions of vehicles travelling with specific velocities on each lane of the road, the lengths of the straight sections of the road and the distance from the observation point. Next, the equivalence problem of replacing the several lanes of the road by a representative single lane is also discussed in detail, as an application of the statistical method. Finally, the values obtained from the theoretical expressions for several kinds of correlation functions of lower and higher orders are compared with experimental values, as obtained by use of the digital simulation technique.