A quiet revolution is under way. By 2007 every major city in Europe must map its traffic noise—and find ways to lower the volume. Paris wins, with a computer model that lights up the town in shades of sound.

How it Works:  The computer model runs on gigabytes of real data: the volume, variety, and speed of traffic on 1,000 miles of streets and roads at all hours; the heights, shapes, and acoustic properties of buildings; and the whereabouts of the city’s 2.2 million residents. A vast software program calculates how the noise propagates and how loud it sounds at each of 26 million virtual microphones throughout the computer city.

The biggest noise source is the Périphérique, an express road that carries 1.2 million cars a day around Paris. Here, abatement walls (blue) on each side keep the noise from spreading into side streets and nearby buildings.


The paving material of a street makes a big difference. Under equal traffic, a cobblestoned stretch of the Avenue de Clichy  (extending southeast from the Porte de Clichy) is 7 to 12 decibels louder than an asphalt portion to the southeast.

 

Some 150,000 Parisians—7 percent of the populace—are regularly exposed to noise levels above 70 decibels from 6 a.m. to 10 p.m. That’s like listening to a vacuum cleaner nonstop for 16 hours.

An estimated 46 percent of Parisians experience noise levels between 61 and 70 decibels, which can cause stress and high blood pressure after prolonged exposure.

 

Sound flows like running water. Inner courtyards are shielded from traffic noise, while outer walls (the Arc de Triomphe, the red building in the lower right corner of the image, ) see a reflected excess of it.