Noise barriers are not regarded with a great deal of affection. In fact, they’re not much regarded at all; perhaps not surprisingly, given that the goal of their installers is to ensure that those who benefit notice neither the barrier nor the noise sources it hides. The majority are basic workmanlike structures, built according to tried and trusted principles: their ability to reduce sound depends primarily on density and dimension. In order to reduce the noise level by about 5 dB a barrier must have 10 kg under each square metre of surface, and be high enough to hide the sound source from view. Adding extra height provides further reductions of about 1.5 dB per additional metre. (A 5 dB reduction corresponds roughly to halving the perceived loudness).
Just like every other kind of noise reducing element, introducing noise barriers at the earliest design stage of a noisy new project is far superior to retrofitting them. But in reality, at least in the UK, most barriers are sticking-plasters rather than structural elements. This is because, by the time anyone (with any relevant authority) realised that roads, railways and airports are none too pleasant to listen to, most of them had already been built. The widespread introduction of noise barriers to UK roads and airports was triggered largely by the efforts of pioneering noise campaigner (and creator of the Noise Abatement Society) John Connell. Hence their usually uninspiring appearance (as you can see in the image included).
But maybe we should learn to love noise barriers, or at least to consider their potential. In principle they offer a canvas for artwork, for the collection of energy (solar, acoustic, vibratory), for noise measurement (and hence sound mapping), for the absorption of chemical pollutants from engines exhausts, for illumination, planting, and wildlife habitats.
Carefully designed noise-barriers can reduce annoyance in other ways than simply by reducing noise. For example, while planting vegetation on the quiet side of barriers will not attenuate noise significantly unless the layer is very deep (it takes about 25 metres of forest to reduce noise by 5 dB), a natural-looking screen can significantly reduce the number of people whom the remaining noise annoys. Installation of such a barrier can have the same effect as a 5 dB noise reduction according to one study, simply because of the positive reactions most of us have to natural (or natural-looking) scenery.
With HS2 on its way, Heathrow expansion on the table, new roads being planned, and old transport infrastructures crumbling, maybe now is the time to rethink our barriers and even — who knows — to love them.
Featured image credit: The elevated Fushi freeway with soundproof wall on the left-hand side, by Hat600. Public Domain via Wikimedia Commons.