I was driving my son Steve back to his apartment near the University of Washington this past Sunday on Interstate 520. As we neared Lake Washington, he asked me to be alert for the change of paving and claimed that it was so quiet that I would be able to hear the engine of my Scion.
We made the transition from old to new pavement and he was, of course, correct. He referenced some signs by the sign of the road which indicated that the new, ultra-quiet paving was part of a test. Further on, just before the bridge, we encountered a second and slightly different test segment.
The road was incredibly quiet, almost eerily so. The Carless in Seattle blog reports that 70-90% of the noise from a car comes from the tires hitting the road.
According to this article in the Seattle P-I, ground-up tires were used in the first segment. Smaller rocks and more of the black “goo” were used in the second segment. Per the article, residents of the up-scale neighborhood of Medina are very happy with the 6 decibel drop in road noise. The ECRD Blog has been tracking this development for quite a while.
At this point the noise-abatement properties of the surface are well-established. Still to be tested is its durability over time.