The Potent Pollution Of Noise

BERLIN, Germany — Thomas Kusitzky’s profession is unusual enough that it has its own consonant-heavy compound German noun: Stadtklanggestalter, or urban soundscape planner. Kusitzky, who believes he’s the only person in the world with that exact job description, works at the Berlin branch of an engineering firm called Müller-BBM Industry Solutions. Most of the company’s staff makes sure new buildings conform to the letter of noise regulations. Kusitzky tries to make them sound good. Which is as hard as it sounds. 

Noise is a potent pollutant, affecting both humans and animals, with transportation and especially cars (not pickleball) the most pervasive culprits. Just as carbon-spewing combustion engines sully the atmosphere and headlights prick the night sky, the low, complex sound spectra generated by motors and the friction of tires on pavement have profoundly altered the Earth’s acoustic environment. 

The World Health Organization associates chronic exposure to noise with “sleep disturbance, cardiovascular effects, poorer work and school performance, hearing impairment” and other adverse outcomes in people. The consequences of unwanted sound are equally grave in the natural world. Its pressures on songbirds — who rely on sound to reproduce — are particularly well studied.

“Chronic noise stresses birds,” said Henrik Brumm, a biologist and head of the Animal Communication and Urban Ecology research group at the Max Planck Institute outside Munich, “and that leads to physiological reactions and health problems. This happens through the chronic stress that results from chronic noise.” (Coincidentally, brumm is the German onomatopoeia for car noise, like the English vroom.) 

Traffic noise has been altering the songs of urban birds for decades. Ornithologists have shown birds singing louder on weekdays when traffic is heavier; shifting the lowest frequencies of their calls upwards to better contrast with the thrum of the vehicles skidding through their habitat; and holding their dawn choruses earlier in the day to avoid being drowned out by airplanes.

Birds unconsciously sing louder when it’s noisy, a phenomenon known as the Lombard Effect, named after the 19th-century French head and neck surgeon Étienne Lombard, who discovered it. But their songs also become less diverse. They’re distracted: One study noted that birds who forage for seeds do so less efficiently in loud environments because they “need to look up more often to scan for potential predators that cannot be heard due to auditory masking.”

Many birds learn their songs by listening to their parents and neighbors and then mimicking their calls. If the surroundings are too loud, they simply can’t hear the entire song, and they end up singing only the higher, more easily audible parts of melodies.  

David Luther, a biologist and ornithologist at George Mason University, has been studying White-crowned Sparrows in the Bay Area for decades. These sparrows used to have three distinct dialects. Now they have one. Luther attributes this to the effect of anthropogenic noise; the surviving tongue had the highest minimum frequency, making it the easiest to hear over the sound of cars.

Bird songs change in the wild, but, Luther said, the White-crowned Sparrow dialect is the only case he knows of where “a dialect, just poof! — it’s all gone.” It’s one tiny, sonic extinction that makes the world slightly more predictable. “It’s a loss of culture,” Luther told me: Like the death of the last person to speak an Indigenous language or to sing an obscure folk song. 

Birdsongs are almost always mating calls, making them essential for reproduction. According to Brumm, the potential correlation between noise and avian reproductive success is a “very important question” facing ornithologists. If “birds can’t continue to sing, they can’t reproduce,” he said.   

Singing isn’t generally considered essential to human reproduction (though music helps). Otherwise, we react to noise pollution in similar ways to birds. The Lombard Effect occurs in people too: We tend to speak at a higher pitch when we’re having trouble being understood. Loud, constant sound wreaks havoc on our concentration. Try to remember the verses to your favorite song near an airport while planes are taking off; try to read a novel on top of a highway overpass. You’ll understand why birds struggle. 

Kusitzky’s city sound design work is focused on people. But unlike the solutions to other problems of our own creation — desperately needed new housing that may encroach on wildlife territory, say — noise mitigation strategies frequently benefit both animals and humans alike.

“When you try to fight noise in general, then animals will definitely profit from that,” Kusitzky said. When he asks human customers what kind of sounds they’d like to hear, birdsong is nearly always at the top of their list. (Rushing water is a close second.) Hans Slabbekoorn, an acoustic ecologist at Leiden University in the Netherlands, conducted a study showing that when people hear birdsong at an open house, property valuations rise. (Not all birds, though: The squawking and cawing of gulls and crows doesn’t have the same fiduciary effect.)

In his recent book “Crossings: How Road Ecology is Shaping the Future of Our Planet,” environmental journalist Ben Goldfarb writes, “Among all the road’s ecological disasters, though, the most vexing may be noise pollution … it has no obvious remedy.” But while there is no easy, overarching solution for our thunderous present, many ways of muting the problem already exist. As with climate change itself, we have the remedies. The hard part is applying them. 

Sound And The City

Kusitzky grew up in a small town called Offenburg near the Black Forest in southwestern Germany. He moved to Berlin in 1996 and two years later began studying jazz electric bass at the Hanns Eisler School of Music Berlin. From there, he moved across town to the Berlin University of the Arts, where he worked on sound art pieces. In 2006, he became interested in urban soundscapes. A student project brought him to the neighborhood of Adlershof, formerly in East Berlin, to study the changing acoustic environment. At the time, Adlershof was in the throes of massive redevelopment. A city planner encouraged Kusitzky and his fellow students to collaborate with a developer who was building new single-family homes. 

Kusitzky interviewed some of the tenants, asking about the sounds they heard in their old apartments and what they wanted to hear in the new ones. “It became clear pretty quickly that it wasn’t necessarily silence that people were looking for,” Kusitzky recalled. “It was a pleasant sound, whatever that means exactly.” One woman told him something that stuck: She wanted to be able to hear her neighbors, but not understand what they were saying.

Fascinated, Kusitzky continued his research into urban sound, co-founding the Auditory Architecture Research Unit (AARU) at the Berlin University of the Arts in 2006. (It was initially an odd fit for the school, as researchers were first placed in the composition department. A few years later, the AARU was moved to the newly created sound studies department.) In 2021, Kusitzky finished his dissertation on urban soundscape planning. A year later, he decided he wanted to do more hands-on work. Müller-BBM Industry Solutions hired him as an acoustic consultant with an emphasis on his unique expertise in urban soundscapes. His first pilot projects with the company, including two large projects in Bavaria, are now in their earliest stages. 

I met Kusitzky on a cold December morning at the Admiralbrücke in the Kreuzberg neighborhood of Berlin. We stood on the snow-covered bridge and looked out over a small body of water called the Landwehrkanal. In the summer, the bridge and the riverbanks are popular for drinking beer, watching people and listening to secondhand Bluetooth-speaker techno music. 

Before the sound of a city can be designed, or even really heard, its noise — meaning, effectively, its car noise — must be reined in. “Noise mitigation is the most important thing, first of all,” Kusitzky said. “First you make sure that it’s not too loud. And once you have that under control, then you have a lot more options for urban soundscape planning.” Kusitzky had picked the Admiralbrücke because the neighborhood had already implemented some effective strategies. 

The most important of those strategies was a series of incremental traffic restrictions, the first of which were implemented several years ago, including movable barriers that block cars but can let emergency vehicles through, pedestrian zones, one-way streets, more crosswalks and school zones, and more restrictive speed limits.

I had walked the short distance from the busy roundabout where the subway station was located to the Admiralsbrücke, and as I waited for Kusitzky, I felt my blood pressure dropping to its normal rate. The pleasant sound — not silence — we heard was a result of not only successful city and neighborhood policies but also abandoned ambitions for growth.

In 1965, West Berlin city planners drew up plans for a highway along the subway route that would have passed about 1,500 feet from where Kusitzky and I were standing. That highway never happened, but a series of large, boxy apartment complexes were built along the road, partially to protect against the wash of anticipated sound. Despite their location in West Berlin, these housing complexes look like something out of a Communist-era spy thriller — and they are strikingly effective acoustic barriers. “The buildings might not be especially popular,” Kusitzky told me, “but they work extremely well at blocking noise from the street and from the subway.” 

This architecture, which results in a space between the parallel walls of two buildings, creates a so-called urban canyon. These canyons are as good at keeping sound out as they are at amplifying the sounds within, as sound waves bounce back and forth between the two close, regular, vertical surfaces. Kusitzky used to live in an urban-canyon-like area not far from the Admiralbrücke.

“If you were standing outside your house at rush hour, you had to speak very loud to be understood,” Kusitzky told me. “It’s not especially pleasant.” I mentioned that birds have to do the same thing. “That’s right,” he answered. “And the diversity of what you’re saying to each other also decreases for people.”

There are ways to take advantage of how urban canyons isolate sound while also reducing how they amplify it. When two buildings are parallel to each other, Kusitzky explained, the walls don’t need to be precisely vertical and regular. “You can offset them or subdivide them to make the sound more diffuse,” he said. “You can use absorbent materials for the façades. Façades made completely out of glass are the worst. It might look good, but it also reflects the sound the most.” 

Summer nights near the Admiralbrücke can become electric with club-like revelry. Many of the older houses near the canal have an architectural feature called a hinterhof, a sort of inner courtyard. These courtyards vary in their aesthetic appeal: Robert Musil, the author of “The Man Without Qualities,” once described the early 20th-century manifestations of these courtyards as “two, three, or four houses showing one another their behinds.”

Today some are pleasingly overgrown, while others are miniscule and mainly used for storing trash. But they have an important acoustic isolating effect against outside noise. “When it’s crowded here and there are a lot of people, it’s always a really nice contrast,” Kusitzky said, as we walked near the water. “It’s really lively here, you hear all the people partying and having fun. And in the courtyards, it’s a bubble of calm.” 

At the nexus of the Admiralbrücke, policies carried through and discarded, designs intentional and haphazard, come together to create a pleasingly multi-dimensional experience of sound. “You hear really beautiful gradations of the space,” Kusitzky told me. “You hear noise that happens close by and noise that is further away. Through the sound, you have a really beautiful sense of the shape of the space.”

But, he added, “you need to make sure that the quality of life in cities lives up to expectations not just inside your own four walls, but outside in the city. That you hear the birds, other people, liveliness. Hearing your own steps when you walk. Along many big streets that doesn’t happen.” 

There’s the need for a literal grounding in space; one we rarely realize we’re missing.

The Asphalt Whisperer

The factors contributing to the pleasant soundscape at the Admiralbrücke are unusual compared to many of the world’s metropolises. Today, Berlin’s architecture is an incongruous mixture of pre- and post-War streets and buildings, with narrow cobblestone lanes and squat buildings adjacent to major thoroughfares and high-rises.

Although Berlin is a big city, it’s also in quiet-obsessed Germany and has a pronounced cultural aversion to noise: A friend of mine who lives in Berlin once received a complaint from a neighbor about her cats walking on the floor too loudly. It also has a largely functioning public transportation system. In much of the world, people are both more dependent on cars and much more exposed to their acoustic excesses. Here, a variety of technological solutions already exist. 

One is what’s known as quiet asphalt pavement, which the Germans more poetically call flüsterasphalt — whispering asphalt. Quiet asphalt has empty spaces within it that helps reduce friction on car tires; because most of the noise cars make above around 20 miles per hour comes from tire friction, rather than motors, the substance can make roads significantly softer.

In 2005, the U.S. Federal Highway Administration sent a team of researchers to study Europe’s use of quiet asphalt, concluding that “the European experience demonstrates that porous mixes are effective in reducing noise when used properly.”

And while there are a variety of different asphalt mixtures in use, the essential mechanism is the same: quiet asphalt “mostly has open pores, so that the sound is practically swallowed up,” Kusitzky explained. “The lamination is also a little different, which makes the vibrations weaker.” 

As with skin, these pores can get clogged by dirt, and when that happens quiet asphalt is just as abrasive as its regular-volumed cousin. It’s also more time-consuming and expensive to maintain. But, as Brumm, the biologist, pointed out, those problems are not disqualifying.

In November, he spent a month in Japan, and an urban planner told him about the rubber (rather than steel) wheels various Japanese cities put on their subway cars. “It’s much quieter, and it’s done to reduce noise exposure,” he told me. “It’s more expensive and it needs more maintenance. But obviously, the Japanese cities and the Japanese government consider it important enough to spend money on.” 

“There are many options” to reduce noise, Brumm continued, “but they often fail compared to economic interests, which are considered more important or given priority over the health of people or birds.” 

Electric vehicles also have the promise to reduce noise on roads. They don’t have motors that go brumm. Instead, their sounds can be programmed to be elegant — at times frighteningly so, as those of us who have nearly stepped headlong into a Prius can attest. But electric vehicles have tires too, so effective noise reduction must combine stealthier cars with quiet asphalt and policy measures like low-speed limits. In 2021, Paris implemented a nearly-city-wide 20 mph speed limit, at which electric vehicles sound relatively unobtrusive. 

More accurately, electric vehicles can run nearly silently; whether they will in the future depends on car manufacturers and their customers. Electric vehicles are a popular segment with luxury manufacturers, who tend to prioritize their customers’ desire to feel special over other participants in traffic. These vehicles must produce sound — extremely quiet early models were deemed dangerous to pedestrians — but what sounds they make are largely up to car companies. (Tesla currently offers seven fart noise options.)

Kusitzky predicted city roads filled with a cacophony of whirrs, slides, synthetic revs and other sounds meant to establish the presence not just of a car, but of a luxury car. “If you imagine 10 electric cars going down the street one after the other slowly, then you suddenly have car companies’ sound branding in the city,” he said. 

Of course, electric SUVs are another issue; these vehicles have larger tires, meaning they again generate more noise at higher speeds.

Even a highway network paved completely with quiet asphalt and driven upon exclusively by appropriately sized electric vehicles, however, is not enough to make roadways places of repose. As one biologist told Goldfarb in “Crossings,” “the best way to preserve quiet habitat for wildlife is to not build the damn road … Once you do, you’re in big trouble.” Goldfarb’s book considers the barriers that keep animals off the highway, so they don’t become roadkill. These barriers must also keep the dull shriek of the highway within its boundaries.

A 2008 study, which Brumm consulted on, examined the effect of a proposed highway near Markgrafneusiedl, Austria. As planned, the road would pass through one of the most important known breeding areas for the Eurasian stone-curlew, a shy, locally vulnerable, primarily nocturnal species largely dependent on sound for communication. (The birds are retiring enough that the ornithologists had to make their baseline recordings at the Vienna Zoo.)

The researchers concluded that only steep earthen walls about 30 feet high would dampen the noise of a new highway enough to avoid significantly interfering with the stone curlews. It was the most intensive of the noise-reduction measures they considered, showing how hard it is to mitigate the sound of a road once it’s there. 

Construction on this highway has still not begun. Austrian courts are considering its impact, with the consequences for the stone curlew a major issue. In many cases, humans and animals have a neatly aligning interest in noise reduction; not so here. The status quo in the village of Markgrafneusiedl involves trucks thundering through its narrow streets, causing traffic, noise and air pollution.

A politician from the region who belongs to Austria’s far-right Freedom Party (FPÖ) complained that experts were “putting the protection of a bird species that no one has even seen for years, and that is hunted in other countries, ahead of the quality of life of the population.” As with physical waste, the question of where to shunt acoustic detritus is deeply political.  

That doesn’t mean humans will always choose their own self-interest over animals’. Luther was recently asked to consult on sound and light pollution for a town council near his home in the suburbs of Washington, D.C. “It’s almost as if people can relate more to animals they see every day, like a bird or a squirrel,” he said, “than other people… ‘That’s them. That’s their problem. But the cardinal in my yard — we want to help it.’”

Consider The Leaf Blower

Sound is invisible, which can make it easy to ignore. A simple first step to combating noise pollution is to conceive of it as physical pollution — with all the ugliness of crushed beer cans in the forest — and to take similar care to avoid it. For Slabbekoorn, the acoustic ecologist, the noise and ecological harm caused by the common leaf blower, reminiscent of a motorcycle race, is not proportionate to supposed safety benefits for, for example, bicyclists and pedestrians who might slip and fall on wet leaves.

“We’re seeing a lot of the songbirds and hedgehogs go down in numbers because you take out that lowest layer in the food chain,” like insects and other organisms that live on those leaves, he said. The small creatures on which birds feed get sucked into the device or pushed away and killed. Hedgehogs, who hibernate in leaves, have their habitat blown away. “It’s not only noisy, but it’s a really stupid thing to do,” Slabbekoorn added.  

He was once vacationing on the Dutch island nature reserve of Schiermonnikoog and enjoying the quiet until someone appeared with a leaf blower. “I guess these people, if they don’t have anything else to do, they go air blowing,” he told me. A change in approach could make this the acoustic equivalent of littering, something frowned on and done furtively.

Businesses and governments already conduct acoustic impact studies; as with other kinds of sustainability reports, though, these vary widely in rigor. One group opposed to the use of a Formula 1 racecourse in the Netherlands approached Slabbekoorn for his interpretation of the track’s noise impact assessment.

When he reviewed it, he saw that the assessment only considered the sound created by the track’s racing vehicles. “Obviously, the cars are just one aspect of the sound,” he told me. “The helicopters, all the people going through that whole area in large numbers — if you want a real impact assessment, you should do the whole thing.” 

Just as engine noise can’t tell the whole history of a racecourse, even intact birdsong doesn’t tell the whole story of a species. When Slabbekoorn used to take the train from Leiden to Amsterdam, he would walk past an area with big, beautiful trees populated by robins. Then one day, the trees were cut down.

The robins continued their song, perching on the bare, barren stumps that were the only remnants of their home. “Most territorial birds, they do not get a second chance” to establish themselves in any area, Slabbekoorn said. “It’s their territory, and that’s for life.” The robins were singing; only it was a dirge.

In contrast, the seagulls I heard squawking while talking to Kusitzky in Berlin were joyful. We’d walked from the Admiralbrücke along the canal to the Urbanhafen, a small former container port. If we hadn’t been discussing sound just then, it might have been difficult to consciously realize the calm I felt: The traffic was rare and slow. The nearby thoroughfare was inaudible. The trees were intact. No leaf blowers sputtered; no Teslas farted. 

Instead, our feet crunched lightly against the cold ground. Small groups of people chatted around us. Kusitzky recalled a day in the ‘90s when the canal froze over, describing to me the sound of skate blades on ice. Swans floated by on the hardly perceptible current. We were in the middle of the city, but the acoustic environment was bracingly crisp and clean. Kusitzky and I spoke softly, about complicated things, and understood each other. 

Nearby, the seagulls continued their squawking. They may have been bad for property values, but they made an exquisite sound.