Turning down the noise: the battle against noise pollution

There is an unseen killer that causes 12,000 deaths every year across Europe according to a 2020 report from the European Environment Agency. The World Health Organization (WHO) ranks it as the second largest environmental cause of health problems after air pollution, and sustained exposure can lead to high blood pressure, heart attacks, stroke, type-2 diabetes, and even dementia. 

The identity of this mysterious killer? It is – perhaps surprisingly – noise, such as that from road, rail, air traffic, and industrial activities [see ‘Sources of noise pollution’]. With one in five Europeans exposed to harmful noise levels, noise pollution is rapidly becoming a public health crisis that has for too long gone unnoticed.

But in the UK, things could be changing. Funded by the Engineering and Physical Sciences Research Council, Noise Network Plus was set up in early 2025 to re-engineer the discipline of engineering, making noise a consideration at all stages of the design process. This interdisciplinary group of engineers, policymakers, industry stakeholders and social scientists is focusing on noise resulting from engineering activities, such as roads, rail, construction, and aviation, as well as energy-generation activities and domestic heating and cooling (such as air source heat pumps). It aims to make consideration of noise a vital component of the design process. 

“Noise tends to be neglected,” says Abigail Bristow, Professor of Civil and Environmental Engineering at the University of Surrey, and Project Lead at Noise Network Plus. “People don’t tend to perceive it as a problem until they come up against it. Noise is all pervasive. It’s everywhere. We can’t get away from it. It affects people’s health in ways they don’t necessarily realise.”

Noise can damage health by triggering stress. Annoying, sudden or overly loud sounds cause the release of stress hormones like cortisol and adrenaline, which alert the nervous system for fight or flight. This evolutionary response used to alert us to danger, but constant exposure to noise, and thus constant exposure to stress hormones, can cause a slew of health problems.

Noise Network Plus was established as part of the UK’s effort to tackle this growing public health problem. The project uses cutting-edge research, engineering and technology to tackle environmental noise pollution. The systems-based approach includes seven working groups that aim to address the challenge from every angle: transport; health and wellbeing; sustainability; AI and digital; education, outreach and skills; inclusive engineering; and policy, law and standards.

According to Bristow, incorporating noise reduction into the design stage of everything – from products to buildings, infrastructure projects, transport and urban landscapes – is a challenge. This will involve reshaping how we educate engineers, architects and urban planners by including noise reduction on the syllabuses of all relevant courses. “I think it’s going to be very difficult,” says Bristow, “because there are so many different branches of engineering, and so many professional bodies who can give the title of Chartered Engineer. Noise doesn’t really appear anywhere in the criteria that these professional bodies ask courses to tick.”

Legislation is another area Noise Network Plus hopes to address. Unlike other environmental challenges such as climate change and air pollution, while regulations for noise exist, they are not joined up so there is no central oversight of how they are addressing the problem.

As Bristow points out, efforts to tackle noise pollution are currently spread across several different government departments, so there is no single body taking responsibility. Noise Network Plus is looking to address this and has already contributed to this year’s Sound Economics report, which reviewed the scale of the acoustics industry in the UK and found that it contributes £5.2 billion annually to the economy. “With this report, we can really start to say, right, how do we reduce noise at the design stage?” says Bristow. “We’ve got the industry here that can do that, and it’s a growing industry.”

Shaping sound waves

Part of that industry is a Brighton-based company called Metasonixx. Founded by Gianluca Memoli, Associate Professor in Sound-Based Interactions at the University of Sussex, Metasonixx uses cutting-edge metamaterials to produce noise-reducing barriers for open spaces like offices and hospitals. Metamaterials are artificial materials whose properties arise from their engineered structure, allowing them to interact with waves (like light and sound) in ways not possible with natural materials. Metasonixx uses metamaterials made out of recycled plastic bricks that can be assembled like Lego to form thin, lightweight partitions (SonoBlinds) that block noise while allowing light and air to flow freely. The resulting panels are positioned in such a way to cancel noise, while the bricks are transparent to light and gaps allow air to move through. 

Inspiration for SonoBlinds first struck Memoli in 2019 on a long car journey with his family. “My kids at the time were very much into the song Baby Shark,” says Memoli, “so that was when I realised I really want a possibility for them to listen to what they want, and for me not to listen.”

Soon afterwards Covid lockdowns arrived, and Memoli realised his idea for sound-reducing barriers would be perfect for lowering noise in overcrowded hospital wards. He approached Innovate UK for funding and developed barriers that could be wheeled into various configurations to provide quiet spaces for patients while allowing light and air to flow through.

Traditional methods for reducing noise rely on blocking it with thick, heavy barriers, absorbing sound with porous materials that trap sound waves, or electronically producing frequencies that cancel noise, as used in noise-cancelling headphones. Metasonixx’s panels work by using the geometry of the structure of metamaterials to filter out unwanted sound waves. The size and shape of the material, which are at microscales, make the sound waves reflect and refract in ways that cancel out certain frequencies, much in the same way that sunglasses polarise out unwanted wavelengths of light. Because they use geometry rather than thickness or density, Metasonixx’s panels are a third of the weight and about a fiftieth of the thickness of traditional barriers. And in 2.5 centimetres they reduce noise by at least 20 decibels, amounting to a 75% reduction in subjective loudness.

SonoBlind is already on the market as a barrier for sound privacy in open offices. Testing in different offices worldwide has shown that after an office has installed SonoBlinds, the workers that cannot concentrate because of noise drop from 70% to 10%. Other potential applications include barriers in factories that filter out machinery noise but allow the sound of fire alarms; windows that block noise but let in light and air; and inserts for ventilation systems to reduce the sound from air conditioners. Memoli is also working on metamaterials for heat pumps noise, hearing aid applications, and designs to reduce traffic noise by attaching panels to car grilles. The latter would reduce engine noise while still allowing airflow for cooling.

Rethinking design

Transport is one of the biggest sources of noise pollution, especially in urban areas, and it doesn’t just emanate from roads. Railways make a lot of noise, as do the projects to build and maintain them. HS2, the new high-speed rail link between London and Birmingham, is the UK’s biggest intercity rail project for over a century, and planners are putting in place measures to reduce the noise created by the trains, once the line is operational. Railways are noisy affairs with engines, rolling stock and track all contributing to the overall sound. But on HS2, where trains will reach speeds as high as 360 kilometres per hour, another source of noise will become even more disruptive.

“The key difference between HS2 and a normal railway is the speed that we’re going to run trains,” says Dr Oliver Bewes, Head of Noise Assessment at HS2. “Noise goes up as trains go faster, but also the type of noise changes. When you’re going at conventional speeds, you’re generally hearing noise from the wheels and the rails. We call that rolling noise. But when trains start to approach 300 kilometres per hour, aerodynamic noise becomes really important – that’s the noise of the air passing over the body of the train.”

HS2 tested a high-speed train in Spain, taking it up to 350 kilometres per hour, and found that at that speed the aerodynamic noise – a loud whooshing sound – exceeded all other sources, coming in at over 100 decibels 7.5 metres from the track, equivalent to standing a metre away from a pneumatic drill. This sound will decay quickly with distance from the railway; however, without control it could still reach levels that will have negative effects on communities up to one kilometre away.

In addition to controlling noise from the train and track, Bewes and his team are designing a noise barrier to cover 48 kilometres of HS2 track in the most sensitive areas. They created a test site at Whittington Heath, just north of Birmingham, where they built a 60-metre mock-up train from shipping containers and a 90-metre concrete barrier. Similar noise barriers are common all over Europe on motorways and railways.

The particular challenge for the HS2 team was to build one that could withstand the uniquely high forces coming from the aerodynamic loads of the train passing, caused by its unprecedented speeds, and ensuring the barrier is optimised to control aerodynamic noise. Using principles similar to metamaterials but at a larger scale, the team experimented with the shape and composition of the barriers to change the way they interact with the sound waves. Experiments included T-shaped and resonating tops to the barriers. Sloping the barrier inwards was also found to improve its performance. Running between three and five metres high, HS2’s noise barrier will be made mostly of concrete but in particularly picturesque sections, such as the Colne Valley Viaduct, it will be partially constructed of transparent glass.

Bewes and his team have produced a prototype and expect to fit noise barriers across the HS2 track over the next two years. Bewes’s research shows the barrier will reduce the sound of passing trains in built-up areas by about 10 decibels, halving its subjective loudness. With its extensive testing of designs and materials, the HS2 team hopes to make a lasting impact, not just on HS2 itself but on future projects. “We’re leaving a legacy,” says Bewes, “making sure that whatever we do now is not forgotten and is used elsewhere.”

The sound of the future

It’s not just traditional transport that will cause noise pollution in the future. Technologies such as drones, flying taxis, heat pumps and wind turbines will all leave their mark on urban soundscapes. One expert researching the sonic effects of these technologies is Antonio Torija Martinez, Professor of Acoustic Engineering and Psychoacoustics at the University of Salford and co-lead of Noise Network Plus, in charge of the transport working group. We don’t usually think of drones as sources of noise pollution but, according to Torija Martinez, as they proliferate they could become sonic pests. “For the same loudness, drones can be perceived as more annoying than jet engines,” he says. “When you set those to the same sound level, or the same loudness, the character of the drone, which is more tonal and higher pitch, [usually causes] more annoyance.”

Torija Martinez’s research focuses on three methods for tackling drone noise. The first is reducing noise at source by designing quieter drones through engineering solutions such as changing the geometry of the drone and the rotor blade design. He and his team found that increasing the angle of the rotor blades relative to the direction of rotation in co-axial rotors (two sets of rotors operating in front of each other with important aerodynamic benefits) reduced their perceived noise level. He has worked with electric aviation company, Greenjets, to study the noise signature of electric ducted fans (EDFs). These are electric-powered fans that produce thrust using electric-powered fans to accelerate air through a cylindrical duct. Using EDFs the propellers of the drone would be covered, thus reducing their noise.

Secondly, Torija Martinez is looking at improving the soundscapes of the future by reducing the noise of autonomous drones and other urban air mobility (UAM) vehicles like flying taxis by optimising their routes. In urban areas, UAMs could follow existing transport corridors so that their noise blends with existing traffic and their annoyance is limited to those areas. 

Thirdly, Torija Martinez uses a cutting-edge area of research called psychoacoustics – the scientific study of how humans perceive sound – to model how people are affected by different variables such as drone design, proximity and routes. “Psychoacoustic models can be useful for decision-making,” says Torija Martinez, “and this can be used to optimise a given design or route so fewer people are affected by noise.” Torija Martinez’s research found that the sound of a quadcopter style drone hovering at low altitude in areas with low road traffic noise significantly increased noise annoyance in bystanders.

According to Bristow, the UK is already ahead of the curve in understanding the problem of noise reduction; now it’s time to turn understanding into solutions. 

In the coming months Noise Network Plus will fund six pilot projects corresponding to its six working groups, pushing the noise reduction agenda forward in the UK. Bristow has an ambitious hope for the projects launched by Noise Network Plus – that they will “halve the damage caused by noise pollution” by 2040.

Reducing noise will be a real challenge but, as Torija Martinez points out, it has never been a more exciting time to be an acoustic engineer. “You are in this situation in history where there are new sources of noise,” he says. “There are drones, heat pumps, wind turbines. And you, as an acoustic engineer, can influence the design. It’s exciting times. You have the opportunity to do things differently.”