The sound of traffic

Above: A device monitors noise levels in a residential neighborhood adjacent to a Quiet Pavement Pilot Program freeway segment. Photo: Arizona DOT. Below: This trailer—built by the National Center for Asphalt Technology—is used to directly measure tire/pavement noise levels using the close-proximity method. Photo: NCAT

The NCAT trailer uses microphones inside a sound-baffled chamber in the trailer to measure noise levels without outside interference. Photo: NCAT

Asphalt pavements constructed with an open-graded friction course have been proven to generate less traffic-related noise than traditional hot-mix asphalt pavements. Photo: NCAT

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