Field Evaluation of Reflected Noise from a Single Noise Barrier (2018) / Chapter Skim
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42 and the meteorological station. Table 13 gives each microphone's position, distance to the edge of nearest travel lane, and height above roadway grade.
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43 The tree and underbrush cover at this site restricted how far back the microphones could be placed. Instead of putting one set of microphones closer to the road, where the direct near-lane traffic noise would dominate, both sets of microphones were placed at the same distance from the road but at different heights.
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44 Source: Research team, NCHRP Project 25-44 Figure 26. I-75 -- BarRef01 (top left)
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Figure 27. I-75 -- cross-sections at Barrier site (top)
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46 Source: Satellite image © 2016 Google Earth Figure 29. I-70 -- microphone positions.
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47 Source: Research team, NCHRP Project 25-44 Figure 30. I-70 -- BarRef01 (top left)
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48 Exact sound-absorption test results for this barrier were not available; however, results for a similar panel from the same company had the sound-absorption coefficients shown in Table 15. Figure 33 shows a site map of the measurement positions.
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49 Source: Research team, NCHRP Project 25-44 Figure 32. I-270 -- No-Barrier view (top left)
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50 Source: Satellite image © 2016 Google Earth Figure 33. I-270 -- microphone positions.
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51 Source: Research team, NCHRP Project 25-44 Figure 34.
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52 Figure 35. I-270 -- cross-sections at Barrier site (top)
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53 Findings: Sound-Reflecting Barriers At the sound-reflecting barrier locations, data were collected under several meteorological classes. Table 17 shows the number of equivalent 5-minute period groupings by site by meteorological class.
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54 Meteorological Class Number of Equivalent Groupings I-24 SR-155 (Briley Pkwy.) I-90 SR-71 MD-5 Upwind Lapse 31 -- -- -- -- Calm Lapse 13 4 -- -- -- Calm Neutral 4 4 4 -- 10 Calm Inversion -- 31 -- -- 15 Downwind Lapse -- -- 12 -- 15 Downwind Neutral -- -- -- 6 7 Total 48 39 16 6 47 Table 17.
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