United States Department of Transportation
i
Investigations of Environmental Effects on Freeway Acoustics [2010]
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2010-03-01
[PDF-3.21 MB]
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Edition:Final report; 05/04/2006-06/02/2008.
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Abstract:The study reported here was designed to examine the impact of background meteorological conditions on the propagation of noise from urban freeways in the Phoenix area. The aim was to understand and predict how sound waves emanating from highways respond to the vertical profiles of atmospheric temperature gradients and velocity shear, so that sound measurements can be interpreted with regard to the environmental variability. Over the course of four days in late 2006 and two days in early 2007, field experiments were carried out at two freeway sites, where meteorological data and sound levels were measured and recorded from early morning until the middle of the day. Such periods span the stable, morning transitional and convective periods of the atmosphere. From the data collected, three test cases of varying atmospheric density stratification and wind shear are presented and discussed. These cases represent all measurement periods and were analyzed in detail.
A parabolic equation model coupled to a Green’s function model close to the source field was developed and used to compute the refracted sound field for experimental cases up to half a mile from the freeway, permitting computations of noise exposure of residential areas nearby. The model demonstrates that atmospheric effects are able to raise sound levels by 10dB–20dB at significant distances from the highway, which at times led to exceeding acceptable limits imposed by Federal Highway Administration for residential areas. Mitigation strategies such as barriers and asphalt rubber friction course (ARFC) are also briefly discussed.
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