Residents living more than a quarter mile from the East Loop 101 Freeway near Scottsdale, Ariz., often voiced complaints about traffic noise levels, especially during early morning and early evening rush hours. However, the Federal Highway Administration’s traffic noise models consistently found the noise to be at acceptable levels.
A new invited paper presented this week at the American Society for Acoustics annual meeting in Seattle by a team of researchers including Harindra Joseph S. Fernando, Wayne and Diana Murdy Professor of Civil Engineering and Geological Science at the University of Notre Dame, helps unravel the mystery.
Fernando and his fellow researchers have been working with the Arizona Department of Transportation to understand these noise issues. Noise measurements the research team made in response to the complaints potentially indicated that atmospheric conditions might explain the high levels residents were experiencing.
“A particular concern of our research is that the Federal Highway Administration’s traffic noise models and policy do not take into account the influence of local atmospheric conditions,” Fernando said. “Urban planners may therefore be underestimating the noise exposure by residents living some distance from the freeway.”
The research team’s collaboration with the Arizona DOT involved field measurements of freeway noise and local atmospheric conditions, as well as the development of mathematical models which can obtain better predictions of the potential noise exposure.
“The computer model clearly demonstrates the importance of accounting for local atmospheric conditions when making predictions of noise exposure near freeways in populated areas,” Fernando said. “The Federal Highway Administration’s noise abatement criterion is ‘67dBA,” meaning that above this level of noise exposure action must be taken to authorities to reduce it. Our results suggest that it may be relatively common to find local atmospheric conditions where such levels can be exceeded in some residential areas at certain times of the day.”
It’s a common site to see noise barriers constructed next to freeways to reduce noise exposure, but the research results obtained by Fernando and his team suggest the barriers might not be suited to the task.
“The fact that significant noise in the case described in our paper is predicted to take a fairly steep path upward to a relatively high altitude of 50 feet, before being directed back toward the ground, suggests that a noise barrier of 8 feet in height would have little effect on mitigating the high noise exposure predicted at three-eighths of a mile from the freeway,” Fernando said.
Fernando and the other members of the research group will continue to examine urban noise pollution and also will examine similar concerns that have been expressed by residents living within a few miles of proposed wind farm sites. The first version of their mathematical model was published in the Journal of the Acoustic Society of America.
Contact: Harindra Joseph S. Fernando, 574-631-9346, fernando.10@nd.edu