The constant roar of traffic, incessant construction noise, piercing sirens, honking horns, shrieking loudspeakers – noise in cities is clearly a nuisance.
But it’s also a danger. The World Health Organisation (WHO) has described noise pollution as an underestimated threat that can cause hearing loss, cardiovascular problems, cognitive impairment, stress and depression. Some experts go further: they believe exposure to environmental noise could be slowly killing us.
“Noise pollution causes hypertension, diabetes, obesity, heart attacks, strokes and death,” says Dr Daniel Fink, chairman of the Quiet Coalition, a community of health and legal professionals concerned with the adverse impacts of environmental noise.
Noise pollution is often cited as one of the main factors in the reduced quality of life in large, 24-hour cities like New York (where more than 200,000 noise complaints were recorded in 2016). It causes stress, which has its own adverse effects on health.
While the impact of noise on mental health has not been studied extensively, research has shown that “strong noise annoyance is associated with a twofold higher prevalence of depression and anxiety in the general population”.
A recent study by experts at the American College of Cardiology linked noise pollution to increased cardiovascular problems (high blood pressure, heart attacks, stroke, coronary heart disease) through the body’s stress mediated response – resulting in the release of the stress hormone cortisol, which in turn damages blood vessels.
At a conference on noise organised by the European commission in April 2017, noise was regarded as “the silent killer”, with potentially severe consequences for our physical and mental health. And yet its impacts remain unreported and underestimated.
Dr Eoin King, assistant professor of acoustics and author of the book Environmental Noise Pollution, calls noise the ignored pollutant. “Environmental noise still continues to be poorly understood by practitioners, policymakers and the general public,” he says.
Most worrying, says King, is the impact on children. “Studies considering the effect that noise may have on children have found that tasks such as reading, attention span, problem-solving and memory appear to be most affected by exposure to noise.”
The issue is compounded by debate over how much noise it is safe to be exposed to. In its Make Listening Safe guide, WHO states that 85 decibels is considered the highest safe exposure level, up to a maximum of eight hours. However, others – Fink among them – argue this is still too loud.
A car measures 70 decibels, a jackhammer 100, and a plane taking off 120, according to the WHO. “Though there is no set threshold to establish risk, we do know that anything above 60 decibels can increase risk for heart disease,” Dr Thomas Münzel, from the Mainz University Medical Centre, has said.
A recent report by the BBC found that parts of the London Underground were “loud enough to damage people’s hearing”, with noise levels greater than 105 decibels on many lines. The report stated that some were “so loud they would require hearing protection if they were workplaces”.
Concerned about increased risk of hearing loss in cities, last year Mimi Hearing Technologies created a World Hearing Index to draw attention to the issue. With the results of hearing tests of 200,000 of their users worldwide and data on noise pollution from WHO and Sintef, a Norwegian research organisation, the index plotted levels of noise pollution and hearing loss in 50 cities.
The study found that, on average, a person living in the loudest cities has hearing loss equivalent to that of someone 10-20 years older. Overall the results showed a 64% correlation between hearing loss and noise pollution.
Guangzhou, China, ranked as having the worse levels of noise pollution in the world, followed by Cairo, Paris, Beijing and Delhi. Of the 50 cities, Zurich was found to have the least noise pollution.
Participants in Delhi recorded the highest average hearing loss – equivalent to someone 19.34 years older than them. Vienna had the lowest hearing loss – but still, on average, that of someone 10.59 years older.
“We were able to collect quite a unique hearing data warehouse on hearing abilities across countries and continents,” says Henrik Matthies, managing director of Mimi Hearing Technologies. “There is an obvious known correlation between being exposed to noise and decreased hearing ability.
“However, mapping this correlation to cities helped us to get the message out, sparking a debate about noise pollution and hearing in megacities like Hong Kong and Delhi.”
But what can be done about it?
“The EU are probably the world leaders at setting out a process to tackle noise pollution,” says King. In 2002, it issued an environmental noise directive that requires member states to map noise exposure in urban areas holding upwards of 100,000 people, to develop noise abatement action plans in these areas and to preserve quiet areas.
Action plans usually incorporate a variety of measures such as traffic management strategies, promoting light rail systems and electric buses, reduced speed limits, introducing noise barriers and improved planning processes.
But good intentions only go so far. “The problem is that there is no real enforcement associated with these action plans,” says King. “Until there is more of a political will to drive planning decision related to noise, I don’t think much will change.”
With road traffic by far the largest source of noise pollution in Europe, affecting an estimated 100 million Europeans, concepts like Paris’s car-free day could have an impact. For one day every month in the French capital, 30% of the city becomes off limits to vehicles. The project has seen sound levels in the city centre drop by half.
“The most effective way to control noise is at the source. If we could make planes, trains and cars quieter we would solve a lot of our problems,” says King. “If all vehicles in a city street were electric, noise would be significantly reduced.”
Increasingly citizens can also do their bit to monitor noise pollution in cities by transforming their smartphones into sound level meters.
The NoiseTube app, developed by researchers at the Free University of Brussels in Belgium, enables users to record where and at what times decibel levels are highest to produce a detailed “noise map” of the city. Councils can use the data to target noise pollution more effectively, using sound absorbent materials such as foam and fibreglass precisely where they are needed most.
King says there are many such projects looking to harness the potential of big data in the fight against noise – “for example, noise complaint data, or social media chatter related to noise, to better assess public sentiments towards soundscapes. There is a lot going on – which I suppose gives us some hope.”