Draft agglomerations noise action plan: consultation

9. Modelling Noise

The Scottish Government has produced noise maps across the entirety of Scotland, showing all areas where people are exposed to high levels of environmental noise, and to support the development of noise action plans.

The noise maps were developed using computer modelling rather than measuring noise. The methodology used is set out in Annex II of EC Directive 2002/49/EC (as amended) and is commonly known as the Common Noise Assessment Methods in Europe (CNOSSOS-EU).

There are several technical and practical reasons why noise maps are normally produced using computer predictions rather than from noise measurements. To produce a map based on measurements would require many measurements to be undertaken over long periods; this would be prohibitively expensive. In most cases, the noise at a location is produced by a combination of different sources. Normal noise monitoring cannot distinguish the contribution from each of these different sources and so noise action planning deciding which source or sources to tackle to reduce the overall noise level is not straightforward.

Noise maps produced by computer modelling can be used to show the noise from individual noise sources. Noise measurements can also be affected by the weather in several ways. Firstly, the source itself might be affected, traffic noise for example has a different characteristic when the road surface is wet and the direction of take-off at an airport might be affected by the wind direction. Secondly, the measuring equipment can itself be affected high winds can generate noise at the microphone. Finally, high winds and heavy rain can themselves be sources of noise from their action on trees and buildings surfaces and these can affect the levels of measured noise. Weather conditions therefore impose a real constraint on the number of days (or nights) when measured noise levels can be relied on.