Draft noise action plans: consultation

Measuring Noise

3. The European Commission's advisory group on environmental noise recommends that Member States use computer modelling rather than measurements when measuring noise.

There are several technical and practical reasons why noise maps are normally produced using computer predictions rather than from noise measurements. This is because 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. These might be, for example, a mixture of, say, roads and railways. 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 prediction 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.