The lightest yellow-orange areas of the map experience an average daily background noise level of 35 to 40 decibels, roughly equal to the hum of a typical refrigerator. The red areas experience more noise — 60 decibels, the level of conversational speech. The blue-to-purple areas see the most transit noise — 80 decibels or more, roughly equivalent to the sound of a garbage disposal.

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Background noise on the level of conversational speech might not seem like that much. But recall that this is the average noise level over an entire day. Evenings may be quieter, but daytime hours will be louder. Imagine trying to get through a day with the sonic equivalent of somebody talking in your ear for every single minute of it.

Airports are the other major source of noise in these maps. See that giant yellow-orange splotch that roughly traces the contours of the Potomac? That's the noise from airplanes taking off and landing at Reagan International, which stands out as the strip of electric blue due south of the “Washington” label.

Highway noise fades quickly as you get farther from roads. But low-flying air traffic can be heard for miles. Zooming out a bit, you can see that the soundscape of the Baltimore-Washington region is dominated by BWI, Dulles and Reagan.

Other cities show similar patterns. Here's the soundscape of the New York metro area, with the airports labeled.

If we zoom in to Manhattan, you can see that Central Park stands as an oasis of relative tranquility amid the din of the city.

One of the unappreciated differences between big metros and rural areas is how much quieter it is out in the country. For instance, here's the noise map showing my current hometown, Red Lake Falls, Minn. (pop. 1,400). It's at the same scale as the Manhattan map directly above.

The BTS says the maps are for “helping policymakers to prioritize noise-related transportation investments” — things like highway sound barriers around residential areas. A 2010 Federal Highway Administration survey found that states have built close to 3,000 miles of sound barriers at a cost of over $5 billion.

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According to the Bureau of Transportation Statistics, nearly 3 percent of Americans live in areas with daily average aviation noise between 50 and 59 decibels. And close to 800,000 Americans live in places with a daily highway noise level of 70 decibels or higher — the equivalent of a vacuum cleaner running every minute, every day for their entire lives.