City Gone Silent

VROOM! A car roars along a busy street. RAT-TAT-TAT-TAT! A worker cracks the pavement open with a jackhammer. WEE-WOO-WEE-WOO! An ambulance blares its sirens. 

These are the sounds you’ll hear in a big city. The hustle and bustle is exciting. But excessive noise, called noise pollution, can harm people’s health. 

In 2016, researchers at New York University began studying noise pollution in New York City (NYC) using high-tech sensors. The project, called Sounds of New York City (SONYC), aims to pinpoint where loud sounds are coming from so something can be done to quiet them down.

During the project’s first four years, the sensors picked up sounds from things like traffic, roadwork, and street musicians. But in the spring of 2020, NYC became quiet. That’s because schools, stores, and offices closed to contain the Covid-19 pandemic. This event, together with other data the researchers had collected, revealed new insights into NYC’s sounds. 

VROOM! A car roars along a busy street. RAT-TAT-TAT-TAT! A worker cracks concrete with a jackhammer. WEE-WOO-WEE-WOO! An ambulance siren blares. 

These are the sounds you’ll hear in a big city. All the activity is exciting. But it can also cause noise pollution. That’s when there’s too much noise. It can harm people’s health. 

Researchers at New York University began studying noise pollution in New York City (NYC) in 2016. They used high-tech sensors to detect sounds. The project is called Sounds of New York City (SONYC). It aims to find where loud sounds are coming from. Then people can work to quiet them down.

The project’s sensors picked up city sounds for four years. They included things like traffic, roadwork, and street musicians. But NYC became quiet in the spring of 2020. That’s because of the Covid-19 pandemic. Schools, stores, and offices closed to stop the spread of the disease. The lockdown also provided new data about NYC’s sounds. 

Like all sounds, the sounds in NYC are produced when a moving object causes air particles to vibrate, or move rapidly. These vibrations, called sound waves, carry sounds to your ears (see The Shape of Sound, below). The height of a sound wave peak is called the amplitude. Louder sounds have taller amplitudes.

All sounds are made the same way. A moving object causes air particles to vibrate. This motion produces sound waves. They carry sounds to your ears (see The Shape of Sound, below). Sound waves have peaks. Their height is called the amplitude. Louder sounds have taller amplitudes.

Scientists measure loudness in decibels (dB). Talking is about 60 dB, and sirens are about 120 dB (see Noise Levels, below). Sounds louder than that can be painful to human ears. “But a noise doesn’t have to hurt to be harmful,” says Rick Neitzel, a noise pollution researcher at the University of Michigan. 

People who are exposed to sounds louder than 70 dB over time are at risk for hearing loss. Loud noise also makes it hard to focus and learn. It can disrupt sleep and increase stress, leading to health problems. 

People outside cities can also be exposed to harmful noises, from things like lawn mowers or farm equipment. To reduce noise pollution, officials need to find what’s making noise and how loud it is. That’s where the SONYC project comes in.

Scientists measure loudness in decibels (dB). Talking is about 60 dB. Sirens are about 120 dB (see Noise Levels, below). Louder sounds can be painful to human ears. “But a noise doesn’t have to hurt to be harmful,” says Rick Neitzel. He’s a noise scientist. He works at the University of Michigan. 

Sounds louder than 70 dB over time can even cause hearing loss. Loud noise also makes it hard to focus and learn. It can disrupt sleep. It can raise stress. These can all lead to health problems. 

There are harmful noises outside cities as well. They come from things like lawn mowers or farm machines. Officials want to reduce noise pollution. But first, they need to find what’s making noise. Then they need to know how loud it is. That’s where the SONYC project comes in.

To measure sound, the SONYC researchers placed sensors in 60 spots around NYC. Each sensor has a microphone that records 10-second audio clips at different times. The sensors contain tiny computers to measure how loud the sound is and guess its source.

The SONYC scientists placed sensors in 60 spots around NYC. Each sensor has a microphone. Sensors record for 10 seconds at different times. They contain tiny computers that measure how loud a sound is and guess its source. 

Over four years, the sensors revealed that sirens and roadwork produce the loudest sounds. Roadwork louder than 80 dB near homes is illegal. The NYC sensors detected roadwork near apartments reaching 96 dB! The city’s sounds also followed patterns: Days were noisier than nights, weekdays were noisier than weekends, and summers were noisier than winters. “There’s a clear rhythm,” says lead researcher Juan Bello. 

Those patterns were disrupted in April 2020, after NYC went on lockdown. The usual traffic rumble dropped. Car honking nearly disappeared. There was just one noisy time period each day starting at 7 p.m. That’s when residents cheered from their windows for essential workers, like doctors and nurses. 

On average, noise levels dropped by 5 dB in the first few months of the pandemic. That may not seem like much. But it was enough to make the city sound like it usually does during a quiet holiday. “It sounded like a sequence of Christmas days,” Bello says.

The sensors showed that sirens and roadwork made the loudest sounds. Roadwork louder than 80 dB near homes is illegal in NYC. The sensors detected it reaching 96 dB! They also found that days were noisier than nights. Weekdays were noisier than weekends. And summers were noisier than winters. “There’s a clear rhythm,” says lead scientist Juan Bello. 

Those patterns changed in April 2020. That’s when NYC went into lockdown. The usual traffic rumble dropped. Car honking nearly died out. There was just one noisy time period each day. It started at 7 p.m. People began shouting from their windows. They were cheering for essential workers, like doctors and nurses. 

Scientists noticed a difference in the pandemic’s first few months. On average, noise levels dropped by 5 dB. That may not seem like much. But it made the city sound like it usually does during a quiet holiday. “It sounded like a sequence of Christmas days,” Bello says.

So far, the sensors have collected more than 150 million recordings. City officials can use this data to reduce noise pollution. For example, now that officials know how loud roadwork is, they could try to keep it below limits. 

The pandemic revealed that individuals can make certain choices to reduce noise pollution, says Neitzel. Adults could choose to keep working from home if they can. They could also walk or bike more instead of driving cars. These changes would decrease traffic noise, like honking.

“Of course, I don’t want to see people locked in their homes just to make a quieter environment,” Neitzel says. “But the pandemic did suggest that it is possible for us to reduce noise pollution by changing our behavior.”

In the meantime, there are ways you can protect your ears. Avoid listening to loud music, and wear ear plugs in noisy environments. “Being aware that noise can be harmful is the first step to addressing the problem,” Neitzel says.

So far, the sensors have made more than 150 million recordings. City officials can use this data to reduce noise pollution. For example, they could work to lessen the loudness of roadwork. 

The pandemic showed people can help too. They can make choices to reduce noise pollution, says Neitzel. Adults could choose to keep working from home if they can. They could also walk or bike more instead of driving cars. These changes would lessen traffic noise.

“Of course, I don’t want to see people locked in their homes just to make a quieter environment,” Neitzel says. “But the pandemic did suggest that it is possible for us to reduce noise pollution by changing our behavior.”

There are ways you can protect your ears in the meantime. Avoid listening to loud music. And wear ear plugs in noisy environments. “Being aware that noise can be harmful is the first step to addressing the problem,” Neitzel says.