Riduzione del rumore da traffico veicolare con barriere vegetali

Noise barriers are frequently being used in recent years to solve problems of noise pollution, in particular traffic noise from highways, above all in urban areas. The insertion loss of different types of natural barriers (an earth mound and a green-wall), constructed on Milan highways network were investigated, to ascertain the role played by the vegetation to increase the noise attenuation, in comparison with a completely artificial panel barrier (made of concrete and plexiglass). The ISO 10847 standard was applied to carry out the measurements, being it suitable to evaluate the noise insertion loss of every type of acoustic barrier, as previously existing as built in-situ. For the earth mound covered by vegetation, an average difference of 2.4 dB(A) between the levels recorded in winter (no leaves) and in summertime (full growth) was obtained, substantially confirming what drawn out from previous similar studies. Nevertheless, the vegetation contribution to noise reduction is remarkably less significant in comparison with the performance of the earth mound with no vegetation (insertion loss of about 10-15 dB(A)) and also that of the artificial panel (about 25 dB(A)). The frequency analysis shows a significant contribution of the leaves in reducing the noise levels in the medium (500 and 1000 Hz) frequency bands. However, it should be taken into account that the vegetation contribution of a barrier is not only represented by the noise attenuation, but also it acts as a sort of filter, able to reduce the air pollution in the area immediately behind the barrier itself, being at the same time a very powerful factor to improve, sometime dramatically, the urban scenery. The possibility to build a natural barrier assumes in this case a strategic importance in a view of a correct environmental management