Turning Down the Volume on Road Traffic
Road traffic produces a great deal of noise, an increasingly frustrating issue for many urban areas. Various traffic calming measures can, however, be deployed with some success. Rowan Watt-Pringle discovers how speed limits and bans can actually have an adverse affect on noise levels, forcing urban planners to rely on intelligent infrastructure to dampen the volume.
Noise pollution is one of the most prevalent sources of environmental complaint in the European Union (EU). Especially in densely populated urban areas and residential areas near highways, railways and airports, according to a 2009 report by Paige Mitchell on the link between speed and road traffic noise, commissioned by the UK Noise Association (UKNA).
Not only is noise pollution an annoyance, but it can also be a significant short and long-term health hazard. The report cites research findings that suggest, "Traffic noise triggers a complex chain of responses affecting human health and well-being."
Rok Ho Kim, occupational health scientist at the World Health Organisation (WHO) Regional Office for Europe, cites a recent WHO study which found that every year in European cities noise pollution causes the loss of more than one million years of healthy life.
"This is comparable with the burden of disease associated to air pollution," reveals Kim, "while in urbanised and industrialised countries such as those in the EU, road traffic noise is the major source of detrimental health effects from environmental noise."
WHO regional director for Europe, Zsuzsanna Jakab reinforces the importance of these findings, saying, "We hope that this new evidence will prompt governments and local authorities to introduce noise control policies at the national and local levels, thus protecting the health of Europeans from this growing hazard."
The UKNA report on speed and noise pinpoints road traffic as the biggest cause of noise pollution in the UK, disturbing more than 12 million people.
More than 210 million Europeans are exposed to excessive road traffic noise.
The report goes on to emphasise some of the more concerning effects of this: "After prolonged exposure (to excessive noise), the impacts of annoyance, stress and sleep disturbance can cause physiological responses resulting in heart disease, high blood pressure and mental illness."
Kim's findings are similarly worrying: “According to the noise maps reported to the EU, approximately 60 million of the 250 million residents in EU cities with a population of over 250,000 are exposed to harmful annual average noise levels (beyond 55 dB during the day, evening and night), causing annoyance, sleep disturbance and cardiovascular diseases," he says.
According to the UKNA report, children suffer some of the most adverse effects of noise: "Traffic noise disrupts hearing, learning and understanding, impacts which are particularly significant for child development. Long term exposure to the level of noise commonly experienced near major roads can cause hearing loss."
Other conditions have been mooted as possible effects of excessive noise, including hearing impairment, psychiatric conditions such as depression and anxiety, and next-day effects of sleep disturbance, such as motor accidents.
The link between speed and noise
The UKNA report states, "There is a measurable link between traffic noise and speed. In urban areas with speeds of between 20 and 35 mph, reducing speeds by 6 mph would cut noise levels by up to 40%," adding that "Reducing 70 mph and 60 mph speeds on urban motorways would cut noise by up to 50%."
The report highlights speed as "the most immediate, the most cost-effective and most equitable way of reducing traffic noise" and goes on to examine several case studies across Europe.
In 2008 in Munich, for example, speed limit reductions were evaluated for one of the busiest roads in a densely populated area. The speed limit reduction from 60 kph (37 mph) to 30 kph (19 mph) was predicted to produce an average 3 decibel (dB) reduction with no change in traffic flow or composition. In the UK, meanwhile, a modelled speed limit reduction from between 60 and 70 mph to 40 mph on the M32 urban motorway in Bristol was predicted to reduce noise by three to 5 dB.
The UKNA report also notes, "Adaptations to vehicles are the most cost-effective and equitable method of cutting speed, as the cost falls on the manufacturer and on the user and not on the public purse."
Addressing the issue of noise pollution from road traffic in urban and other areas, however, is not as simple as merely lowering the speed limit. As a spokesperson from the Irish National Roads Authority (NRA) explains, "Noise from road traffic comprises engine-related propulsion noise and rolling noise from the interaction between tyre and road. At higher speeds, rolling noise is predominant, while at speeds less than 30 kph, engine noise becomes dominant."
This means reducing speeds in the higher range, when rolling noise is dominant, will decrease traffic noise levels. "However, reducing speed limits from 50 kph to 30 kph (31 to 18 mph) has the potential to increase noise levels, because you are going from predominantly rolling noise to a situation where engine noise is dominant," he points out, adding the percentage of heavy goods vehicles can also result in higher noise levels.
In addition to loudness, the health impacts of noise depend on duration, predictability, pitch and context. Sudden or sharp noise peaks can be as or more annoying than overall noise levels, especially at night when they disturb sleep.
The UKNA report therefore emphasises that traffic noise impacts should be measured not just in terms of overall levels, but also peaks, as well as the noise frequency, or pitch.
Accelerating and braking influence overall traffic noise and noise peaks. "Noise events caused by aggressive or heavy-footed driving stand out from the anonymous background, and can have a disproportionate effect on the perception of noisiness," the report explains, adding not only that "acceleration is more significant than braking and its importance is greater at lower speeds," but that acceleration can account for as much as 10% of all traffic noise.
The report additionally states that traffic speeds, volumes and vehicles make up the driving environment - the other main factor in traffic noise - for driving patterns like acceleration and braking, with these patterns also being dependent on driver behaviour and vehicle design.
The size of the road is another factor to consider, with the UKNA report claiming "there is evidence to suggest that traffic noise, certainly in urban areas, has become predominately a main road problem. Many 'residential' roads have been traffic-calmed, cutting traffic volumes, speed and, usually, noise."
Reducing road traffic noise
The Irish NRA reveals there are many approaches used to reduce road traffic noise. "Firstly, if we look at the source of the noise - in other words, passenger cars, buses, trucks and other vehicles - manufacturers have made significant improvements in engine and braking technologies, meaning that in general cars, buses and trucks are now deemed quieter than ever before," says their spokesperson.
"Many countries are installing low-noise asphalt pavements as well as noise insulation street barriers in densely populated areas. Low-noise tyres are also now available on the market. These measures are shown to be very effective in reducing the levels of road traffic noise, especially when they are used in combination," Kim divulges.
Road surfaces have improved significantly in recent years. Low-noise road surfaces now have the ability to reduce noise levels by up to 5db, while some of the more specialised surfaces can achieve even greater reductions.
"As well as treating the source, there are measures that can be used to reduce the noise levels reaching the receiver," the NRA spokesperson goes on. "These include propriety noise barriers, walls, contoured noise embankments, façade insulation and urban design where buildings are designed so that habitable areas are located away from the source of the noise."
Kim believes that until now awareness about noise pollution among policy-makers as well as the public has been too low, pointing out, "In urban environments, air pollution and chemical contamination are decreasing, also as a result of national and international efforts supported by the WHO, whereas noise pollution is on the rise and will become increasingly important in Europe in the near future."
Despite this, progress is being made, with Kim continuing, "In 2002, the EU parliament passed a directive on environmental noise (European Noise Directive, 2002/49/EC), while other EU directives aim at reducing noise from motor vehicles, tyres and other relevant consumer products."
He adds that most European governments, including the 27 EU countries, comply with these EU directives, while most European cities with more than 250,000 inhabitants have developed strategic noise maps and action plans to reduce road traffic noise according to the European Noise Directive.
Intelligent infrastructure will become increasingly central to traffic noise reduction as technologies are refined. Already, motorways are being equipped with active traffic management technology, allowing traffic managers to monitor conditions, while intelligent speed humps that automatically adjust their height to counteract the weight and speed of a vehicle can help to reduce noise and vibrations loads on busy roads.
'Drive slow go faster', according to the UKNA report, is "an urban traffic flow measure which involves road re-design and lane narrowing to reduce speed and prevent overtaking." In urban areas, in-car speed limiters such as intelligent speed adaptation (ISA), can help to "reduce harsh acceleration and the incidence of speeding when roads are not congested," while eco-driving techniques help to lower noise levels and can be enhanced via in-car information that promotes even driving patterns.
Kim believes there is plenty of room for technological advancement to reduce road traffic noise: "Important engineering innovations to reduce noise at the source and during transmission are often neglected because of the costs involved, so further investment in the use and development of cost-effective technologies could bring additional health benefits," he states.
The NRA highlights possible ways to reduce noise in the cities of the future, including better public transport systems to reduce the number of vehicles on the road, as well as an increased presence of electric vehicles, which are significantly quieter at lower speeds and are well-suited to city driving.
Improved urban planning, meanwhile, can ensure that people do not live overlooking major roads.
"Where this is not possible, people could live in buildings specifically designed to attenuate noise and protect their inhabitants," postulates the NRA's spokesperson. "As research continues into the effects of road traffic noise, new innovative noise barrier designs should also help to reduce noise levels, with one example being sonic crystal noise barriers, which can reduce noise in a particular range of frequencies, meaning they can be calibrated to dampen specific noises."
Kim concludes, however, we should not merely rely on technology, as tackling urban traffic noise should be viewed within the wider perspective of sustainable urban transport policies. "In this context, policies that promote less dependency on cars in favour of public transportation, cycling and walking, are those that deliver the greatest number of benefits for the urban environment and health, by addressing multiple issues such as road safety, congestion, control of emissions and greenhouse gases, land use and noise."