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Suggested Citation:"Abstract." National Academies of Sciences, Engineering, and Medicine. 2016. Field Evaluation of Reflected Noise from a Single Noise Barrier—Phase 1. Washington, DC: The National Academies Press. doi: 10.17226/23457.
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Page 13

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x A B S T R A C T This research studied the change in sound levels and characteristics caused by sound reflections off a reflective (non-absorptive) noise barrier on the opposite side of a highway. The analysis was done using measurements at five Barrier sites and adjacent sites without a barrier under equivalent site, source, and meteorological conditions. Changes in broadband and 1/3 octave band equivalent sound levels (Leq) were studied, along with statistical descriptors, particularly the L90 and L99 metrics. Evidence is seen of increased Leq both across the road from the barrier and at positions between the road and the barrier. In some cases, even greater increases in L90 and L99 suggest a sustaining of the received sound due to the reflections. Spectrograms, visualizations of the spectral time history, reveal that the presence of the barrier causes sound levels to increase over a broad range of frequencies and causes higher sound levels to be sustained for a longer period of time. Psychoacoustic metrics were calculated and combined into three measures of annoyance. Annoyance metrics opposite the barrier tended to increase relative to the No Barrier site in lighter traffic where individual vehicle passbys are distinct.

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TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 218: Field Evaluation of Reflected Noise from a Single Noise Barrier—Phase 1 studies the change in sound levels and characteristics caused by sound reflections off a reflective, non-absorptive noise barrier on the opposite side of a highway.

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