![]() ![]() However, their effectiveness in terms of noise reduction is minimal with 10 m depth of vegetation resulting in only 1 dB reduction in noise. Vegetation can also be used as a noise barrier. The varying height is designed to create destructive interference effects that will reduce noise propagation over the barrier, i.e., the jagged edge causes a reduction in coherence of the diffracted signal being transmitted to the shadow zone as compared to a conventional straight edge barrier ( Samuels et al., 2009) Random edge profile barriers are barriers with different height along their length. The Sound Tube along the Tullamarine Freeway, Melbourne, Australia. ![]() In some European cities, barriers that partially cover the road have been used, but these are very expensive architectural features.įigure 7.10. Barriers are relatively ineffective at screening properties at some distance from the road as the barrier effect is not additional to the attenuation due to propagation over the intervening soft ground instead, the barrier replaces this component of noise attenuation ( King and O’Malley, 2012). However, in practice, a noise barrier will reduce noise levels by 3–7 dB, depending on their design and height ( Arenas, 2008). ![]() ISO 9613 limits the maximum attenuation of a thin noise barrier at 20 dB in any octave band and 25 dB in the case of thick noise barriers. The mechanisms behind how a noise barrier attenuates sound are discussed in more detail in Section 2.6.4. The effectiveness of a noise barrier is governed by the path length difference (the amount by which the top of barrier cuts the line of sight between the source and receiver), provided the sound transmitted through the barrier is minimal. In fact, noise barriers, including earth berms, are the dominant type of mitigation measure adopted in CEDR member states 2 to reduce road traffic noise ( Bendtsen et al., 2010). Despite barriers being costly, they are used frequently to reduce noise propagation alongside roads or railway lines. The first purpose built noise barriers were built in California in 1968 and, since then, noise barriers have steadily grown in popularity to mitigate against noise, with ever increasing research in the science of noise barriers ( Pilton et al., 2006). Noise barriers are generally seen to be an effective means by which the propagation of noise can be mitigated. King, in Environmental Noise Pollution, 2014 7.5.3 Barriers ![]()
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