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A study of Greater London linked loud traffic with strokes and other health problems.

The environmental cost of car-reliance in cities typically focuses on air pollution, and all the damage particulate matter does to human lungs and lives. But road noise also has an impact on health and well-being—and it’s hardly a trivial one, as shown by new study published in the European Heart Journal. Let’s take a closer look at what the research team calls “the largest study to date to investigate environmental noise and cardiovascular disease in the general population.”

What they did

The public health scholars, led by Jaana Halonen of the London School of Hygiene and Tropical Medicine, focused on the Greater London area inside the M25 ring motorway—a study population of some 8.6 million residents. They modeled annual traffic noise from 2003 to 2010 along some 63,000 road links. They split the noise into daytime (7 a.m. to 11 p.m.) and night, and categorized it as being below or above 55 decibels, a health threshold established by the World Health Organization.

The researchers studied the link between health and road noise for all Greater London inside the M25 ring motorway. (European Heart Journal)

The researchers layered this data with hospital visits for cardiovascular reasons, heart disease, and stroke, as well as deaths falling under these classifications. They looked at the entire population of adults over age 25, as well as a subset of the elderly over 75. Last, they gathered measures of poverty, smoking (estimated via lung cancer mortality rates for an area), and air pollution—variables that might confound the role of noise on health.

What they found

Simply put, Halonen and company found that road noise had a measurable impact on the health of Londoners. Adults in areas where the daytime traffic noise exceeded 60 decibels were more likely to be admitted to a hospital for stroke, compared with areas where sound didn’t hit 55. Among the elderly, daytime road noise was also linked with admissions related to cardiovascular disease, and night noise was related to stroke admissions.

Meantime, in all London adults, daytime road noise was associated with an increase in all mortality causes in areas over 60 decibels, compared with places under 55. Adjusting for air pollution had only “minor effects” on the findings. The authors conclude:

In one of the Europe’s largest cities, we found that long-term exposure to daytime road traffic noise was associated with small increased risks of cardiovascular disease and all-cause mortality in the general population. Strongest associations were observed between daytime road traffic noise and hospital admissions for stroke, particularly in the elderly (≥75 years).

What it means

As for why road noise has a possible impact on health, the researchers offer several possibilities in line with previous studies. Sounds from the environment might increase heart rate, blood pressure, and stress, among other things, with these impacts having a cumulative effect on health over time. The role of noise in high blood pressure, in particular, might explain the high risk of stroke in those living along the loudest corridors.

There are caveats; first and foremost, a statistical analysis like this one can’t say for sure whether noise directly caused the health outcomes. Though the researchers tried to control for outside variables, it’s very difficult to remove the strong roles of socioeconomic status and air pollution from health outcomes. Last, the noise models used by the study group couldn’t account for things like place of work; daytime road noise won’t bother you at home, after all, if your office is somewhere else.

That said, the findings fit well with previous studies of traffic and health. While there have been relatively few studies of traffic sound and severe illness, according to the researchers, most of the ones that do exist show the same sort of negative outcomes found in the London population. Any full reckoning of the social cost of city driving must take this convincing body of research into account.

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