If you can’t enjoy your garden or backyard due to excessive road (or other) noises, there are a few things you can implement to try and reduce it.
This is a long post – I went a bit overboard on the research – so if you’re after a straightforward summary of how to block road noise, here it is:
The best way to block road noise is to reduce noise at the source:
- Reduce traffic speed
- Change the road material
- Alter traffic conditions/behaviour to reduce acceleration and braking ‘intensity’
- Reduce the number of large vehicles or overall traffic volume
If you have no ability to influence or change these conditions – say through petitioning your local council – then build walls.
Solid walls work best to block noise. The closer to the source of the noise, the more effective it will be at reducing it in your yard. Exceptions are if you sit at the top of a slope above the road, in which case a wall at the top will have a greater effect.
Ensure you completely block the road from view. Sound bends around and over walls. The taller the barrier, the more effective it will (likely) be.
The construction of the wall (NO GAPS!) is more important than material choice in many cases. That said, thicker materials (like bricks or stone) absorb sound better. Ensure the surface of the wall is rough or irregular – rough surfaces reflect and diffract sound more effectively than smooth.
Use plants – hedges like Juniper work well – to help soften additional sounds that creep around your wall. Plants are not as effective as people believe at blocking road noise, but work well in conjunction with walls.
Finally having ‘white noise’ sources in your garden/ backyard – such as water fountains or speakers playing soft music/sounds – helps drown out similar frequencies coming from the road. Have these things as close to you/ your area as possible.
I’ve gone into more detail for each of these snippets below.
So if you want to learn more about all of it, or perhaps just a section on design, construction or perhaps material choices, you can follow the links below to access each section, and subsection, directly.
- Start By Changing Traffic Conditions
- Brick And Concrete/Cinder Blocks (CMU’s) Are The Kings Of Noise Reduction
- Do Sound Proof/ Acoustic Fences Work?
- Would Steel Fence Panels (Colorbond) Work?
- What About Regular Timber Fences?
- Want Something A Little Different? Try Rammed Earth Walls
- Do Plants Block Road Noise?
- If You Have The Space, Consider Soil Berms/ Mounds To Block Road Noise
- Add Water Features To Your Yard To Drown Out Some Road Noise
- Or Use Speakers To Play White Noise
- Combine Different Noise Blocking Options
- Wall/Fence Construction
- Designing Your Fence/Wall To Effectively Block Road Noise
- Don’t Forget The Other Side Of The Road!
- And Don’t Forget Graffiti
The Science Of Noise
I thought I’d start with a little run through on how sound ‘works’ and why understanding the basics can help you come up with a better wall or other design.
Firstly, sound is often measured in Decibels (dB).
This works well for engineers who care about the strength of a sound, but we humans don’t hear all frequencies ‘equally‘ – e.g. we hear midrange frequencies clearer than low range frequencies, which are diminished.
To take this into account, when measuring noise humans will hear, an additional weighting is added. The weighting increases and decreases sensitivity to different ranges of frequencies.
The ‘A’ Filter applies to midrange frequencies (giving less weight to low and high), while the ‘C’ Filter applies to low and high (less weight to middle).
For our purposes, the A Filter is more important as it is used to measure hearing loss. So many of the studies I read, and link to, use dBA as the standard.
Another thing to note with dB/dBA is it is a logarithmic scale.
A reading of 70 dB is double the perceived noise level of 60 dB.
And 80 dB is double 70 dB (and 4 times 60 dB).
The increase in ‘intensity’ or power of the sound is actually a lot greater (10 – 100x) but for our purposes, perceived sound is more important.
This means seemingly minor reductions in dB or dBA levels will have a pretty significant impact. Reducing road noise by 10 dB effectively halves what you hear.
Sound Is Like Water
It’s easier to think about how road noise is reaching you if you imagine it a little like water, with waves rippling out from the source/s.
These waves either reach you directly – in a straight line – or indirectly – reflecting off or bending around surfaces (known as diffraction).
We’ll see in the design and construction section how thinking of sound like water helps you understand how to build your ‘wall’ (whatever materials you choose to use). For now, keep in mind that whatever you build to block road noise won’t fully block it.
You will still have sounds that reach around and over your wall. The aim is to minimise perceived noise levels overall, and you may need to use multiple layers and methods to do that.
Reflection And Diffraction
Reflection is when a sound wave hits a surface and bounces off.
On a smooth surface, the angle it hits = the angle it leaves/ reflects. You can take advantage of this fact by ‘roughing up’ the surface, so waves don’t reflect straight into your yard. Or opt for a material that absorbs sounds better.
This matters more if you have a wall or surface on the other side of the road to you. Not only will you pick up noise from the side of the road near you, but you may also pick up traffic from the far side, where it reflects off the wall and enters your yard.
Diffraction is when a sound wave encounters an object – or gap – and bends around it.
Low pitched sounds (with long wavelengths), like trucks rumbling by, will bend around and through spaces better than higher pitched sounds, which don’t diffract as much.
So if high pitch sounds like horns or other things are affecting you, a wall will work very well at reducing those noise levels.
The GIF below clearly shows this diffraction phenomenon in action.
You can see the softer waves in the bottom right corner – this is, ideally, where your garden and house are located. The taller the wall, the longer the ‘shadow’ it casts. We’ll look at this in more detail in the design and construction section.
Another thing to be aware of with diffraction of sounds. When there is a small opening or gap, sound waves will flow through it, bend, and quickly fill the space behind – spreading out to cover the space.
Technically this will occur if the wavelength of the sound is larger than the opening size. But for our purposes, this means you need to ensure that there are no gaps in the wall.
At ground level, between materials, or at the edges.
Otherwise, you may end up with a level of perceived noise that is basically the same as the traffic on the other side of the wall.
Why Are Roads Noisy?
Now that you know a little bit about how sound operates, let’s have a quick look at why roads are noisy in the first place.
The answer seems incredibly obvious – it’s traffic. But there are a few factors that can change how you approach blocking sounds – depending on your local traffic conditions.
In reality, road noise is made up a combination of rolling noise (tyres interacting with the road) and propulsion noise (engines, exhausts, transmission and brakes).
Let’s look at these factors, and some of the individual elements within them.
As I said, rolling noise is basically vehicle tyres slapping the road.
Since you have even less control over changing vehicle tyres than you do changing the road surface material, we’ll ignore that part of the equation.
As a general rule, rolling noise is the biggest contributor to noise levels for cars travelling above 55 kph (35 mph) and trucks above 70 kph (43 mph).
The above figures can change a little depending on the other element in this equation – the road surface material.
The less porous a road, the louder it will be. One study found concrete was consistently louder than asphalt, with the difference increasing at higher speeds.
This is especially true for larger vehicles. As this article suggests, not only do they make more noise overall at higher speeds, but as they get even faster, large vehicles make more noise than a similar car with the same speed increase.
Some places around the world are looking at making roads with more porous surface materials, to help absorb the different noises that are produced by vehicles. But that is unlikely to be something within your control, even if your council is willing to make changes.
So the main takeaway here is the faster vehicles go, the more important the road material becomes in producing (or reducing) road noise.
Propulsion noises refer to not only the physical elements within the vehicles, but to driver behaviour as well.
We saw speed mentioned above, but one thing that can dramatically add to road noise is the acceleration and braking patterns drivers take.]
Reducing how quickly people slow down and speed up can have a big impact on reducing noise levels overall, especially across hundreds of vehicles.
I also mentioned speeds above – when rolling noise contributes to overall road noise.
The flipside of that coin is for vehicles below those speeds (55 kph or 70 kph), these propulsion noises – engine sounds, exhausts, brakes and transmissions – will have a larger impact on road noise.
So if the road outside your yard already has a low speed limit, then vehicle type (what vehicles make all these propulsion noises – e.g. trucks, cars or motorbikes) will have a big impact on overall road noise.
This may make it harder to reduce noise at the source – because you can’t get everyone to change cars, or what types of vehicles go past your house.
But the upshot is, given vehicles are travelling at lower speeds, the road noise level may low enough that the methods we look at will be relatively effective.
What is The Best Way To Block Road Noise?
There are a few ways to really reduce or block road noise. Let’s have a look at your options going from best to worst.
1. Start By Changing Traffic Conditions
We’ve seen from some of the science above that reducing road noise at the source can make a huge difference to overall noise levels. This approach is probably the best at reducing noises that reach your yard, but it comes with the obvious caveat that it’s out of your control.
The reason I want to cover it is your best option (and probably cheapest for you) is to approach your council and petition them to implement some of the changes outlined below.
Now I know that isn’t always an option, but for some of you it may be something you hadn’t considered before. And seeing it here may save you a tonne of time and money.
If this is something you think could work, it might pay to measure and log road noise across time in different parts of your yard. So you can give the council some informal data to at least start discussions.
If you suggest this approach to your neighbours, who knows? You may end up with a cohort of citizens who push for action, which is harder for a council to ignore.
I took a number of the measures below from this great little ‘Speed and Road Traffic Noise Report’ by Paige Mitchell, commissioned by the UK Noise Association. Despite the slant it may have, the proposals it outlines sound pretty solid to me.
The main ways to reduce road noise are:
- Lower vehicle speeds
- Reducing speed limits through signage (e.g. lowering the legal limit and show on signs – no alterations to the road)
- Reduce speed limits through temporary limits that change depending on traffic conditions or the time of day/night
- Adding speed bumps (round tops are best – flat tops can increase sound levels)
- Night time restrictions on heavy vehicle driving
- Reducing the number of road lanes to prevent overtaking
- Change the road surface material
- Changing from concrete to asphalt reduced road noise by around 1.5 – 3 db, according to this study, depending on the speed of the vehicles
- One option may be the previously mentioned porous road surfaces to reduce ‘slapping’ sounds from vehicle tyres at high speeds
- Prevent excessive braking and/or accelerating
- Reduce the rate of acceleration and braking as vehicles approach intersections, bends, streets etc. through physical road changes or engineering (traffic flow) changes – such as changing red light patterns in the local area
- Reduce traffic volume
- Not just overall volume of vehicles, but the types of vehicles
- Less heavy vehicles producing lower frequency sounds
Note, things like rumble strips, speed cushions, or cobblestones can in fact increase the level of road noise.
So be wary of accepting those options unless whoever suggests them can provide solid evidence they will make a difference.
The first choice – reducing vehicle speeds – can have a dramatic impact on reducing traffic noise. If you need more convincing (and given you’re here I don’t think you do) I’d encourage you to read through the Speed and Traffic Noise Report I mentioned above to get an idea of the figures.
The last point – reducing traffic volume – is probably the least effective of the bunch. The report above suggests to cut the sound produced by 2000 vehicles (over one hour) in half, you’d have to get down to just 200 vehicles.
So cutting traffic can help, but hopefully not at the expense of an increase in rolling and propulsion noise. You’re better off trying some of the other options rather than rely solely on reducing traffic volume.
Interestingly, there appears to be a threshold for large vehicle volume (as a percent of overall traffic volume).
Going from 1% to 10% large vehicle volumes in local traffic sees a pretty substantial increase in road noise, particularly if speed bumps are implemented.
But going from 10% to 20% sees a barely noticeable increase. Perhaps this is due to larger vehicles, at low speeds, producing lower frequency sounds, which we don’t hear as well? I’m not sure, but it’s something to note.
This doesn’t mean more large vehicles won’t make a difference – I’m sure having 50% volume will cause problems. But it doesn’t appear to be a linear relationship.
2. Brick And Concrete/Cinder Blocks (CMU’s) Are The Kings Of Noise Reduction
These walls/fences are your strongest, most effective options at blocking road noise.
Unfortunately, they are also your most expensive.
This is even more of an issue in colder climates, where you need to have your footing below the frostline.
Additionally, building any large brick or concrete block wall/fence on your property is likely to require a check-in with your council.
They may have specific guidelines around the style and appearance of fences – which can limit your material or construction options – to ensure you don’t stand out too much.
Depending on the height you want to build to, you may need a building permit, which will also add time and money to an already expensive project.
There are a number of different ways to construct brick and concrete block walls, but the basic theory is the same.
Dig a trench, fill it with some form of reinforcement – like a steel cage – and pour your concrete foundations. You may have steel rebar uprights – for concrete blocks – and/or piers – for brick.
Both options have ‘staggered’ courses so the block is always laid covering two blocks below it. This strengthens the wall, preventing cracking in the mortar from running all the way up the side.
Concrete block walls are generally a little cheaper and quicker to build, but often require an additional finish – like rendering or veneer cladding. Cladding refers to a tile, stone or other ‘finished’ product you will stick to the outside face of the wall.
Another benefit of cladding is you can clad the wall with a rough or uneven surface. This may help reflect, diffract and absorb road noise even more effectively.
Brick walls are generally left finished as is, so they look like… bricks… but you can sometimes add a rendered finish.
3. Do Sound Proof/ Acoustic Fences Work?
Acoustic fences are a somewhat new style of panel wall. These are designed to be constructed like regular metal/ colorbond fences – e.g. upright posts with panels between.
This makes them cheaper than brick or concrete block walls in many ways, one if which is no need to build footings along the length of the wall – only the uprights.
I can’t personally vouch for how effective acoustic walls are, but the theory behind them seems… sound…
Anyway, they are usually made of a dense material that absorbs sound waves, using the same principle you’d find in recording studios.
If you are using these, you still need to ensure you follow good design principles (NO GAPS!) that we’ll touch on below. But, if you do live near a noisy road, these walls, along with some additional planting, may be a good option for you (if you have suppliers in your area).
4. Would Steel Fence Panels (Colorbond) Work?
Steel or Colorbond fence panels would operate in a similar manner to the acoustic walls above, but perhaps less efficiently.
They are thinner, so wouldn’t absorb sound in the same way. In fact they’re more likely to simply reflect it, and allow some to diffract over and around it.
You would also need to make sure there are no gaps between panels and uprights, or beneath it at ground level.
Beyond that, depending on the kind of noise you are getting, a colorbond fence paired with plantings may be enough – and probably cheaper than other options above.
5. What About Regular Timber Fences?
If your noise issue is minor – not requiring some of the approaches above – you may be able to get away with simply fences made from timber.
Timber fences could be done in two ways:
One is a normal timber paling fence like the example above. Like steel panel fencing, you need to ensure there are no gaps between slats, or below the fence.
The second is something slightly more heavy duty – uprights with timber laterals, like you often see for retaining walls.
The appeal of using timber laterals is you may be able to make the wall thicker than a normal paling fence. The downside is it can be challenging to ensure there are no gaps.
To ensure as few gaps as possible, you may need to opt for tongue-in-groove cuts, or perhaps overlap them on the outside, like a roof tile. Anything to prevent gaps forming and sound seeping through.
Another issue with timber fences is they don’t last as long as other options. Fire, rot and termites can take a toll, especially to those areas below ground level. Although timber is usually treated against this, it is something to be aware of.
Despite these concerns, pairing a timber fence with a layer of plants may be enough to suitably block any road noise you hear. And it’s likely to be the cheapest option.
6. Want Something A Little Different? Try Rammed Earth Walls
Having looked through some of the more common wall options already, I thought I’d throw in something a little different. Rammed earth as a construction technique has a lot of benefits and has been around for thousands of years.
From a noise blocking perspective, I suspect it could suit the purpose very well.
In theory you can make the walls dense and thick, and perhaps even rough up the surface to help with sound reflection and diffraction.
That said, I haven’t seen rammed earth residential walls used for this purpose. Generally, they pop up on more rural properties where there is more space.
This may not matter so much, but building the walls does involve large amounts of formwork, equipment and specific ratios of soil/clay/cement.
Despite that, I thought they’d be an option worth sharing in case you thought they might be suitable for your site.
You could create something unique and beautiful for you to look upon – and for those driving by to enjoy…
7. Do Plants Block Road Noise?
You may be wondering why it’s taken so long to talk about plants as a way to block road noise.
Well, the reality is they are less effective at blocking sound than you might think.
Even the most dense foliage won’t fully reflect sound, meaning any kind of consistent road noise is likely to leak through the hedge, or even multiple layers of plants.
Remember the notion that sound is like water? Imagine attempting to stop a flood of water flowing through a hedge. That’s how sound worms it’s way through.
All that said, plants – like Juniper hedges – are still useful at helping dissipate some of the sound that reaches your yard.
As we’ve noted a few times, having a layer of plants after a solid wall can act like a silencer – diffracting the sound waves even further. You could even try a row on the road side as well.
Despite not being a great first option, one thing plants do is remove the road from sight – and often much cheaper than other fences listed above.
This psychological gain can lower the perceived level of sound you experience, which may be enough to help you out.
Out of sight, out of mind in some respects.
There is plenty of information online about suitable hedges for your area. Or you can ask a local expert to suggest a few thick hedges or screening plant options.
If you do want to plant a hedge, but don’t want to wait five years before you have a somewhat effective block in place, you could plant it behind a temporary barrier.
The idea is to have a screen block the view (and protect the immature plants) while the plants grow.
Once they reach maturity you could remove the barrier/screen, leaving you with a lovely mature hedge/screening plants etc. to continue the job.
So despite plants inability to block noise well on their own, they work well in concert with other walls/fences we’ve explored above.
Whether that’s to diffract or silence sounds further, or for purely aesthetic purposes, plants are a useful material to use as part of your noise reducing project.
8. If You Have The Space, Consider Soil Berms/ Mounds To Block Road Noise
These are probably only viable on larger properties, but may be the most effective measure out of anything we’ve looked at so far.
Soil berms are basically mounds of soil that are build up like little hills.
They may be expensive if you need to hire the earth moving equipment to create them (not to mention the soil you may need to actually build them).
But they could work well if you build them tall enough.
Adding plants on top of a dense, thick mound of earth would work quite well in reducing road noise.
9. Add Water Features To Your Yard To Drown Out Some Road Noise
So far we’ve covered a lot of fence style approaches that attempt to block road noise at or close to the source.
Another method works well is to try and drown out some of the noise in your yard with ‘white noise‘. And a great way to achieve this is by using a water feature.
The sounds the water feature produces are probably mid to high frequencies – tinkling and bubbling – that may help cancel out some of the more annoying sounds you may hear from the road.
A good way to think about a the role of the water feature is to imagine it as a pair of noise-cancelling headphones – only less efficient.
Noise-cancelling headphones work by creating a sound wave that is similar to the source sound wave (so traffic noise), but an inverse (opposite) pattern.
Through a process called destructive interference, the headphone waves cancel out the source waves.
If the water feature was close to the road, you’d need to be as loud (that is, the sound needs to have the same power) as the road noise. But, the further you move away from the road, the less powerful the water feature sound waves have to be.
So if you’re entertaining/sitting area is some distance from the road, you want to have your water feature close to you. The closer it is, the softer it can theoretically be – e.g. it doesn’t need to work as hard to drown out some of the road noise.
Now attempting to achieve true destructive interference in open 3D space is very challenging, and outside even more so. So while the concept is the same, a water feature is not as efficient as a designed active noise control system would be.
10. Or Use Speakers To Play White Noise
Instead of a water feature, you could opt for some outdoor speakers or sound system that plays music or other noises.
This approach may be useful if you want to try and target a consistent level and type of road noise. You could position the speakers and play white noise or nature specific tracks or playlists.
You could even test this approach yourself, before you buy anything. Try some white noise playlists in headphones, or with a small portable speaker. See if it has any noticeable impact on perceived road noise levels.
I’m not an expert in sound engineering, so you may want to talk to professionals who could help you choose the best system and layout for your circumstances.
This article looks at choosing suitable outdoor speakers and provides a few interesting options. It does focus more on entertainment rather than noise attenuation, but the hardware/systems are the same.
11. Combine Different Noise Blocking Options
If you are dealing with a particularly noisy road, my recommendation would be to combine as many of these options as possible.
1. Start with approaching council about reducing noise levels in the first place.
2. Look at using solid barriers – the thicker and denser the better – to reflect much of the sound as close to the source as possible.
3. Add layers of plants like hedges to soften any sounds that make it past the fences/walls.
4. Place white noise generating elements close to your sitting area – things like water features and/or speakers playing softer sounds.
Having determined what approaches and material options might work best for you, it’s time to consider the design and construction of your project.
Why Design And Construction Of Your Barrier Is So Important
I mentioned right at the top that in some cases, the design and construction of your barrier is more important than the material you choose.
That’s not to say the material is irrelevant. As we’ve seen, generally the thicker and denser the material, the better it will reflect and absorb sound.
But, if you have a poor design and/or construction, you’ll end up with an expensive place to hang things, rather than a barrier that is successfully reducing road noise.
This paper provides some useful information around blocking noise from roads (specifically section 2. Acoustic principles of noise wall design in NSW).
It may be worth having a look through, so you get a better sense of how this department approaches larger freeway noise wall design.
I won’t detail specific construction methods, as I’m not an expert. Rather, your focus with anything you construct – regardless of material – is to ensure there are no gaps.
This will be easy for some materials – like brick and concrete blocks.
Others, like timber paling, laterals or any sort of panel/screens (colorbond etc.) may appear ‘sealed’, but may not be in reality.
This may require careful checking along each seam – between uprights and panels, or between palings – or perhaps even adding sealing elements as part of the build.
Remember, think of sound like water. You wouldn’t simply nail tiles together in your bathroom. You want mortar and sealant to ensure nothing seeps between them. Think of these fences in the same way.
Designing Your Fence/Wall To Effectively Block Road Noise
When it comes to designing any kind of fence, wall or barrier, you MUST check with your local council for any specific rules or regulations you need to be aware of.
You may need to stick to specific material combinations.
Or you may have fence height restrictions.
Or maybe you have easements on your property.
All of these will be constraints you need to work within, before you design your wall to reduce road noise.
That aside, what do you need to focus on when designing your wall?
I’ve mentioned previously that the higher the wall, the better the noise reduction.
To clarify this further, especially if you are not on a straightforward level site, imagine someone standing in the middle of the road, and someone else standing in your yard in or near your main sitting area.
Whatever barrier you erect, you want to block these people from seeing each other.
This is why if you are on a slope above the road, you actually need to move the wall closer to you, rather than closer to the road itself. If you have it too close to the road, these people can basically look over the top – even over a 2m (6ft +) wall.
One thing to be careful of, in your quest to build a giant wall, is if you inadvertently block out the sun, or nice breezes, or perhaps nice views.
This can be a tricky thing to manage, so take some time to understand your site, where these elements come from, and what your wall and potential hedge will do to alter the site.
Especially the sun – don’t put yourself in the dark if you can avoid it.
If you have no alternative, maybe look at other places you can place your entertaining area – so you can still build a suitable wall/fence, but get some sunlight.
Check out this post on blocking neighbours from view to learn more about designing things ‘out of sight’.
For most people, the length of any wall or fence will be as wide as you can go.
When you meet neighbouring boundaries, you may be able to connect to their walls/fences – again remembering to plug gaps as best you can.
Though in some cases, you may find your neighbours don’t have high fences. Or you are on a large property where fences are far away, and you want to shield yourself as much as possible.
In this case, you can follow two rules to improve the sound reducing qualities of your wall.
First, ensure the wall is long enough to cover a distance 160 degrees in front of your building.
The further away the wall is placed, the longer the fence is going to be. If this makes your wall excessively long, you may need to bring it closer to your house.
The second approach is to add 90 degree ‘returns’ on each end of the wall.
Turning the ends back towards the house is useful if you run out of space on your property, and your neighbours have no noise blocking elements.
Simply run the walls back similar to the image above, until you can cover roughly 160 degrees from a point in your site.
Now you don’t need to choose the dead centre of your house. You may be better off using the centre of your outdoor sitting area and roughly trace out 160 degree lines from there.
By focusing on making your wall/fence tall enough and wide enough – plus NO GAPS! – you should be able to create a good first layer to block a large portion of incoming road noise.
From there you can add layers of plants, water features and other elements mentioned above.
Don’t Forget The Other Side Of The Road!
There is one last thing to think about when it comes to blocking road noise.
As I mentioned previously, if you have a wall on the opposite side of the road to you, traffic noise will reflect from that wall, and can add to the road noise seeping into your yard.
One way to deal with this is to see if you can ‘rough up’ that wall surface, to reduce the reflected sounds you might receive.
Or add some softening materials to it like plants. Or, if a new one is being built, opt for thick, noise absorbing materials like masonry.
Obviously if you don’t own, or have no control over this wall/space, you can’t try those approaches. But it’s worth knowing this reflection can occur, so try to address it at the source if you can.
Perhaps a discussion with neighbours or council can lead to a small change on their end for a big quality of life improvement on your end.
And Don’t Forget Graffiti
As sad as it is to bring up, it’s important to think about acts of vandalism and graffiti. You may spend thousands of dollars and find some jerk ends up tagging your wall with an incomprehensible scribble.
Again, you have little control over someone doing it, but you can think about trying to prevent it.
Rough or uneven surfaces are often harder, or less satisfying, to graffiti – so that may be something you think about on the road side of your wall.
That said, rough surfaces are more difficult to clean that smooth. So although you may lower the likelihood of being graffitied, you increase the difficulty of cleaning them.
Another option is to try and plant a climber along it, hopefully growing out and preventing access to the wall.
A third option may be to get ahead and have an artist create street art, or a mural, on the wall. People are less likely to tag existing work. But I understand if this isn’t for everyone.
So this is the end of the guide on how to block road noise in your garden.
Hopefully you found some useful information and ideas on how best to deal with your noisy road situation.
If you do discover other useful materials, designs or construction techniques, please feel free to comment below. You may have come up with the perfect solution for someone else!
Finally, if you’d like to learn more about adding a fence or wall to handle noise as part of an overall, full site design, check out any of my guides; the free 6 Step Beginner Guide, or either of my ebooks -my Landscape Design 101 Guide or The Garden Design Process.