The map below, made by Kurt Fristrup of the National Park Service, shows the loudest (yellow) and quietest (blue) places in the continental United States:
Not surprisingly, cities tend to be very noisy, with background levels averaging around 50 to 60 decibels. And that's just the average: heavy truck traffic can reach around 85 dB, while construction jackhammers can reach 95 dB if you're standing less than 50 feet away.
By contrast, regions like Yellowstone National Park have background noise levels down at around 20 decibels, which is about as hushed as things were before European colonization.
So why does any of this matter? For starters, all the artificial noise and light that cities produce can have bizarre effects on humans and wildlife — effects we have yet to fully understand. Loud cities can interfere with the ability of owls and bats to hunt. And, because of urban noise, some male birds now have to sing at higher frequencies, making them less attractive to potential mates.
Even humans aren't immune: The World Health Organization has argued that "noise pollution" can muck up our sleep patterns and lead to higher stress levels and heart disease. That's why many European countries regulate noise levels like pollution — the Netherlands requires low-noise pavement on certain roads. (The US, by contrast, has no federal noise standards.)
The map above was commissioned by the National Park Service's Division of Natural Sounds and Night Skies to identify places where artificial noise may be affecting birds and other wildlife. It was first shown at the 2015 annual AAAS meeting. The researchers took recordings of background sounds from areas around the United States and used that to model sound levels for the entire country. You can see a bit more about their research here.
-- Light pollution is erasing the night sky. Can we bring it back?
-- Loud headphones are making us prematurely deaf