Traffic movements generate noise. Three sources contribute to this noise: engine noise, noise from the contact between tyres and road surface and aerodynamic noise. The relative contribution of each of these sources depend on the vehicle type and the speed that the vehicle is travelling. The standard methodology in the UK to establish the levels of noise generated by traffic is set out in the publication “Calculations of Road Traffic Noise” (London, 1988, Her Majesty’s Stationary Office).
When used in EIA the methodology is usually based upon an 18 hour time frame and therefore requires 18 hour traffic flow information. To calculate accurate source levels information about the road surface, number of vehicle movements, their average speed and the percentage of HGV’s is required. To calculate the actual noise effect on sensitive receptors further information is requirement about the make-up of the environment between the road link and the receptor. Factors that influence the noise level at the receptor include the distance between the road and the receptor, the presence of a geographical gradient, the presence of objects that may act as a barrier and the kind of surface material on the ground.
When considering one single road link and a limited number of sensitive receptors, for instance when considering the noise impacts associated with the construction of a new road, a simple spreadsheet calculation could suffice. However when introducing multiple receptors in a network of road links, the set of calculations rapidly becomes complex. In these situations a dedicated software package, such as SoundPlan, should be used. These software packages can provide detailed spatial analysis of the levels of traffic noise experienced at any location within the study area.