Environmental noise is considered a serious pollutant in urban areas, and is known to be a cause of various ailments ranging from stress to heart disease. With three out of four Europeans living in or near cities, the issue affects hundreds of millions of people. Ines Lopez Arteaga, a researcher at the Department of Mechanical Engineering of the Technical University of Eindhoven, discusses potential solutions.
Where does the noise in cities come from?
Ines Lopez Arteaga: The main sources are transportation and industrial sites. In urban environments, road traffic is the main culprit, followed by rail traffic and aircraft. Then there are construction sites and noisy neighbours, which are mainly a source of annoyance.
Why is urban noise a serious health risk ?
Long-term exposure to transportation noise increases the risk of hypertension, ischaemic heart diseases, tinnitus, cognitive impairment in children, sleep disturbance and annoyance. Studies have shown that noise levels above 65 decibels – think heavy traffic at a distance of 50 to 100 m – increase the risk of stroke by 20–40%. At these levels the risk of heart disease is also 20% higher than for people living in quieter areas. By comparison, a typical conversation takes place at about 60 decibels.
The World Health Organization has calculated that in Western Europe more than one million healthy years of life are lost every year due to traffic noise. This means that long-term exposure to traffic noise is, after air pollution, the main environment related health stressor, compromising quality of life and indirectly the life expectancy of millions of people across Europe.
What can be done about it?
First, you need measures to reduce the amount of noise produced by transportation and, second, measures to minimise noise levels at the target location. To achieve significant noise reductions, you need a combination of measures at the source and reduction of transmission to the receiver. Obvious examples at the receiving end are double-glazed windows and noise barriers like those you see along many highways across Europe.
An example of a reduction measure at the source is the use of double-layer porous asphalt – or “silent” asphalt – on roads, which reduces the actual noise made by the tyre, while also absorbing the sound due to the tyre-road interaction. This type of surface is already in use in many European cities, including Paris, Amsterdam and Madrid.
Another example – on railways this time – is vibration dampers on wheels and rails. Elastically embedded track systems can be found in the tram networks of The Hague and Antwerp. Studies have shown that such vibration dampers, as well as the use of asphalt roads, can reduce noise levels by between 2 and 5 decibels, which is significant.
Noise expert Ines Lopez Arteaga
“Studies have shown that noise levels above 65 decibels – think heavy traffic at a distance of 50 to 100 m – increase the risk of stroke by 20–40%.”
What solutions might be put in place in the future?
Two examples are rubberised roads and green roofs. Rubberised road surfaces – which are different from silent asphalt – make use of rubber-like materials to bind stones, and are more flexible than regular road surfaces. Such roads already exist in Japan and the US. Promising tests have been run in Europe, for example on the ring-road around Brussels.
Another solution is the greening of roofs and walls. Materials suitable for growing plants soften the urban environment through sound absorption, keep sound levels low, and have the potential to significantly reduce traffic noise in urban courtyards. Greening is not yet applied as a means of noise reduction, but is in my view a promising future concept.
Will electric vehicles help reduce noise?
Only somewhat. With their relatively quiet motors, electric vehicles can help reduce noise in city centres, where speed limits are low. This won’t be the case, though, for people living close to ring-roads and highways. At speeds above 50 km/h, tyres rather than engines are the main source of noise. And above 130 km/h, aerodynamic noise dominates.
How did you become involved with environmental noise?
During my PhD research on railway noise, I developed technical solutions to design more silent wheels for trains. Later I extended my research to understanding noise generation by car tyres.
Initially, my aim was to help manufacturers provide better products. But with both train wheels and car tyres, you quickly realise that improvements to the tracks and road surfaces are needed to achieve large-scale noise reduction. So, I started to interact with the infrastructure and government stakeholders, and became interested in the overall challenge of environmental noise.