HIGHWAY NOISE IS PREDOMINANTLY FROM YOUR CAR'S TIRES INTERACTING WITH THE SURFACE AS IT TRAVELS OVER THE ROADWAY.
On the original concrete pavement, the roadway’s surface was textured with transverse grooving that created a very objectional tire whine. The interaction between transverse grooves and tires creates noise. It was not the concrete pavement that was responsible for Arizona's road noise, but rather the transverse grooves making up the surface. Diamond ground textures are oriented in the direction of driving and do not produce the objectionable tonal spikes produced by transverse grooved textures. Diamond grinding removes noisy transverse grooves and makes pavements quieter.
An example of how transverse grooving causes noise can be seen in the 2008 Honda Civic Musical Road, where grooves were cut into an asphalt roadway to play the "William Tell Overture." Fast forward to 02:22 to skip the introduction.
DIRECTION OF TRAVEL
Transverse Texturing - Original Highway Texture
Diamond Grinding - New Highway Texture
NOISE AS A QUALITY-OF-LIFE ISSUE IN THE VALLEY
By 2000, ADOT realized highway noise was a quality-of-life issue for citizens and responded by undertaking significant noise research.
ADOT evaluated six asphalt and three concrete surfaces, constructing test sections of each. ADOT’s research predicted an increase in asphalt rubber noise levels of approximately ½ decibel per year. As a result, ADOT engineers recommended quiet concrete surfaces, which do not experience an increase in noise over time to the extent that asphalt rubber does.
In 2003, ADOT created the largest quiet pavement research program in the U.S. After 15 years, this research validated the original ADOT research prediction that asphalt rubber increased approximately ½ dBA per year in noise level. This means that in ten years it will be 1.5 times louder than when constructed.
Asphalt rubber is slightly quieter for seven to eight years and then becomes increasingly louder than diamond ground concrete. Since a three-dBA difference or greater is needed to demonstrate a perceived difference in noise, this slight early-on advantage is insignificant after only a few years.
AUTO INTERIOR NOISE LEVELS AT 65 MPH
Newer diamond grinding noise level
Older asphalt rubber noise level
To put these numbers in perspective, the six-dBA difference means that the asphalt rubber produces an interior noise 1.5 times louder than the diamond ground concrete surface.