GETTING THE MEASURE OF ROAD NOISE IMPACT

The authors review some of the problem areas, explain some of the methods and examine the effectiveness of noise protection measures. The problem associated with the subjective attitude to noise change and its relation to the existing noise are discussed. It is suggested that, although the 18 hour l10 unit is normally used to assess noise impact, the change in l90 noise level may be a more realistic measure. Below 67.5db(a) there is no entitlement to noise insulation. Noise can be reduced by the erection of a noise barrier, by quietening vehicles or by the use of quieter road surfaces. Noise barriers can typically reduce noise levels by about 5db(a) and TRRL research has shown that textured macadam surfaces can reduce road noise by between 3 and 4db(a) concrete roads are generally about 2db(a) noisier than the noise produced by black top roads. An example is given of the method of assessing the need of a noise barrier which requires the calculation of noise levels with and without a barrier and with different lengths of barriers. The costs of house price depression payments must also be assessed and balanced against the cost of protection measures. However these are areas such as parkland and public open spaces where the economic type of assessment is not applicable. (Author/TRRL)