Living next to a road or busy development can cause a lot of noise pollution, which in turn can affect human health. However, building sizeable concrete barriers around roads and other noisy areas isn’t exactly ideal. This is where the likes of plant walls and using natural barriers have become a more sustainable alternative. Natural plants and other wildlife can create barriers to reduce noise pollution, such as in cities or around busy roads, whether that be trees, bushes, shrubs, or a combination of natural elements.
A research study conducted by Ankara showed that noise reduction of 15 dBA (Decibel Adjusted) was in fact possible with certain plant materials. They even researched the most effective types of plants that could be used to prevent noise pollution. The research even showed that 250 metres of dense shrub cover has the potential to eliminate noise from any major road.
While under UK law there is no legal limit to road noise, it is taken into consideration when new houses, offices, or even roads are planned. In fact, land purchased for relief roads must include a compulsory purchase of excess space to make way for noise pollution barriers and similar areas.
Since November 2012, there have also been laws on tyres. Tyres are now graded to show how noisy they are and there are even restrictions on how much noise a tyre is allowed to make. Likewise, it is illegal to modify the exhaust system to make a vehicle noisier after it’s been approved or checked to make sure it upholds environmental and safety standards. When these noise regulations are ignored, the police can take action, especially if you’re caught creating excessive noise.
Despite regulations regarding traffic noise, this doesn’t mean that living near a road is ever quiet. Homeowners living next to a major road network, whether that’s a carriageway or even a motorway, will often say that noise affects their property, whether indoors or outside.
But how could plants and trees help reduce noise?
Research in a variety of cities from places in America to Ankara in Turkey has shown that vegetation, as well as being aesthetically pleasing and good for the environment, is also a helpful barrier to preventing excess noise.
Choosing the right trees, such as evergreen trees and shrubs because they will remain a prominent feature in your landscape all year round, is of incredible importance. A tree, such as an oak tree that sheds its leaves every year, will not be as effective in reducing noise as a pine tree.
Sometimes called a ‘sound belt’ or a ‘sound barrier’ or even a ‘buffer’, these dense collections of trees are effective against lowering the sound levels emitted from nearby roads. Trees are also effective in reducing some of the carbon dioxide being released into the atmosphere.
It’s worth it if you’re considering planting a sound barrier to look at whereabouts the barrier needs to be planted. In cases of road rails or airports, the sound barrier should be as close to the source of the noise as possible. For a busy road, a barrier would be, for example, better positioned on the banks, sloping from a road to absorb the sound waves early on. Start with small bushes and shrubs branching up into larger trees as you reach the bank and near any housing developments or urban areas.
It’s also worth considering whether you need public access. Is there a public footpath or similar in the area? This can restrict how many trees can be planted, or whether access needs to be planned and put through such an area. Historically, there are often footpaths crossing major roads, such as A roads. These previously weren’t as large and crossed now-major networks, and these footpaths were sometimes the most direct route connecting villages.
It’s also worth considering upkeep. How do you upkeep a bush or tree shrub area that is directly next to a road? Do you need to install steps, or do you need to create access and a slight gap from the edge of the road to the bank?
Some types of trees, such as the Acer, have been shown to be effective in reducing noise pollution. Researchers in 1980 found that certain types of Acer were all effective in producing noise reduction up to 10-12dBA (decibels adjusted). These include:
The common Alder tree (Alnus glutinosa, Alnus barbata), Hybrid Strawberry Tree (Arbutus andrachne), Swedish Birch (Betula verrucose), Common Horbeam ‘Pendula’ (Carpinus betulus), Cornelian Cherry ‘Variegata’ (Cornus mas) and Hazel ‘Fuscorubra’ (Corylus avellana) were also shown to be effective at reducing noise pollution in built-up areas.
Complement these with a variety of bushes such as holly (Ilex aquifolium) and other ferns and other native shrubs, and you have a well-designed and precise noise barrier.