The roar gets louder as the plane gently soars into the sky over the new building of the Swiss Tropical and Public Health Institute (Swiss TPH), which lies right on the flight path of Basel’s EuroAirport. Depending on the time of day, planes thunder over the building as often as every five minutes — so, where better to talk about noise limits? One of the institute’s researchers is environmental epidemiologist Martin Röösli, whose work focuses on noise and mobile communications. Among other things, Röösli helped compile a report by the Federal Noise Abatement Commission (FNAC) that delivered a key recommendation: Switzerland needs new noise limits. Although the report has now been in the hands of the Federal Department of Environment, Transport, Energy and Communications (DETEC) for almost two years, no action has been taken.

Limits for road, railway and aircraft noise are subdivided based on how the respective area is used — for example, by industry, as a recreational area or as mixed commercial/residential space. For typical Swiss city centers, the noise limit stands at 65 decibels during the day and 55 decibels at night. These levels were originally defined in the 1980s. “Back then, noise research simply didn’t exist — there were only subjective surveys,” says Röösli. “The basic principle was that, for a noise to be classified as too loud, it had to be perceived as irritating by at least 20% of respondents.”

At what point does noise become harmful?

The World Health Organization (WHO) guidelines are derived using a different approach and are stricter than for Switzerland. WHO levels are 51 decibels during the day and 45 decibels at night for road traffic — with even lower recommendations for aircraft noise. These levels are not only determined by asking “at what point does it become irritating?” but also “at what point does it become harmful?” Thanks to long-term epidemiological studies, this question is now easier to answer than it was 40 years ago: Continuous noise, particularly at night, can trigger psychological and physiological stress and therefore an increased risk of cardiovascular diseases, obesity, diabetes and depression.

"You might imagine that health damage occurs suddenly when the defined limits are exceeded. Apparently, that is not the case." - Martin Röösli

If it were up to the Noise Abatement Commission, noise limits would also be reduced in Switzerland: to 47 decibels at night instead of 55 in mixed commercial/residential areas, for example. Where do these figures come from? “You might imagine that health damage occurs suddenly when the defined limits are exceeded,” says Röösli. Apparently, that is not the case: “Rather, what we’re dealing with are continuous curves.”

Valuable long-term data.

In areas where endless streams of traffic churn through the city, noise isn’t the only problem: You also don’t really feel like taking in lungfuls of air. People living on arterial roads are exposed to exhaust fumes as well as noise, and the effect of this exposure is the subject of research by Nicole Probst-Hensch, Professor of Epidemiology and Public Health at Swiss TPH and the University of Basel. Probst-Hensch and her colleagues have been conducting the “Sapaldia” cohort study since the early 1990s, when the researchers began asking the same group of people in Switzerland questions about their lifestyle and health.

These regular batches of survey data are fed into mathematical models along with air measurements from the respondents’ places of residence, allowing researchers to identify relationships between risk factors and impacts on health. The Swiss Cohort Study on Air Pollution and Lung and Heart Diseases in Adults (Sapaldia) has delivered some significant findings and is set to continue, now as an integral part of international projects with the same objective.

All of these studies paint a clear picture: the greater the exposure, the greater the risk of cardiovascular diseases, chronic respiratory problems and diabetes. Yet, this too prompts the question of how to define a limit if there is no threshold below which health effects are absent altogether.

Mixed effects and compromises.

It requires some challenging statistical effort to pick apart the mix of environmental influences and to ascertain which of them are potentially harmful enough to require urgent regulation. Some of these influences may also be more harmful in combination than they are alone: “One key focus of our research is on the interactions between — and the combined effect of — different pollutants,” says Probst-Hensch.

"The maximum permissible exposure should therefore be chosen to protect the weakest in society." - Nicole Probst-Hensch

The situation is even more complex when you consider individual differences in the population, such as pre-existing conditions or a genetic predisposition. “The maximum permissible exposure should therefore be chosen to protect the weakest in society,” says the environmental epidemiologist. And yet the limits are not set at zero.

The permissible levels of noise and airborne pollutants are based on compromises — as we learn in our conversation with Martin Röösli, who is well acquainted with the process of setting these upper limits. After all, the levels must be balanced against other societal needs, such as mobility and living space. “Limits have a major impact, including on the economy. For example, you can’t build any new homes in places where limits are regularly exceeded.” In light of these and similar considerations, the political debate around the modification of Swiss limits could potentially even see them increased. Such fears may explain why the FNAC report is the “hot potato” that no one dares to touch.

Probst-Hensch is also in favor of moderate regulation despite the corresponding health risks. No matter how harmful vehicle emissions are, fine particulate matter and soot also arise within our own four walls when we light candles or fireplaces. “At the same time, however, open fires and candles have a positive impact on well-being, and you can always improve a fireplace’s ventilation. I don’t think it makes sense to restrict their use.”

After all, stricter limits are just one of many concerns addressed by commissions such as the FNAC, and Röösli is confident that these wide-ranging needs can be reconciled through technical advances — whether it’s quieter car tires, low-noise asphalt or better-soundproofed windows with ventilation technology that brings purified outside air into rooms. Some of these advances are already in evidence at the new Swiss TPH building. Indeed, around a dozen planes must have roared over the institute during our interview — and we didn’t hear a thing.