In Europe, road noise causes ill health effects, including high blood pressure, said Gert Ahe, director of the Danish Road Institute. Pavement noise causes reduced housing values, and in many households, the noise exceeds the threshold of annoyance. While noise is an unsolved problem on existing European roads, noise planning is integrated into the design of new roads and housing developments. And several European countries have begun following the European Union Noise Directive, which calls for a 10-year plan with measures intended to mitigate the problem.

For the European Scan Tour, a group of industry and governmental officials studied pavement design and noise levels in Denmark, the Netherlands, France, Italy, and the United Kingdom, said David Newcomb, vice president of research and technology at the National Asphalt Pavement Association. "In every country we visited, road noise is a significant annoyance," said Newcomb. "Every country had maximum or target noise levels on pavements. All of them are working to meet the EU Directive, and everyone has noise legislation or a policy in place. Every country we visited is using quiet pavements."

In this country, the National Center for Asphalt Technology has embarked on a multi-year research program with two goals, said Douglas Hanson, senior materials engineer with AMEC, an international consulting firm. NCAT wants to develop technology to design a low-noise pavement surface, and to be able to use that technology to provide economical solutions to highway design problems without arbitrary rules, Hanson said.

NCAT developed a close proximity noise trailer, which places microphones close to a test tire and measures the sound that emanates at highway speeds. Hanson has tested noise levels on 250 different hot-mix asphalt sections and 70 concrete pavements. Pavements have been tested in 18 states, including California, Colorado, Arkansas, New Jersey, Ohio, and Texas.

Average noise levels of hot-mix asphalt, as measured close to the tire by the NCAT trailer, read as follows: (If the noise was measured by the far field method away from the tire, the noise levels would be much lower

Dense graded HMA, 97 dB(A), or decibels, a measure of sound amplitude.
Stone matrix asphalt, 97 dB(A).
Fine open-graded friction courses, 92 dB(A).
Coarse open-graded friction courses, 95 dB(A).

"In general, the finer the gradation used in an HMA mix, the quieter is the pavement," Hanson told attendees at Quiet Asphalt 2005. He said it is possible to build a low-noise HMA pavement surface, and that pavements have a noise signature — frequency in hertz plotted verses noise level in decibels. "Plus, the noise level of a pavement will increase with time, but we don’t know by how much," said Hanson.