The National Academies Press

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From page 58... ... 58 The state of the practice in the United States is to model sound levels, evaluate noise impacts, and design noise abatement measures under neutral meteorological conditions (no wind or temperature effects) Read the entire page →
From page 59... ... Implications for Noise Impact and Abatement 59 The research team evaluated the measurement data at the reference microphones to identify the worst noise hour. Traffic on I-17 during the worst noise hour is approximately 7,000 vehicles per hour (vph) Read the entire page →
From page 60... ... 60 How Weather Affects the Noise You Hear from Highways Table 19. NCHRP Report 791 temperature profile classes. Read the entire page →
From page 61... ... Implications for Noise Impact and Abatement 61 Noise Impact Results The research team evaluated how noise impacts and noise abatement conclusions might change under different meteorological conditions. This required the following inputs from the user: • Impact and noise barrier feasibility and reasonableness information from an SHA noise policy. Read the entire page →
From page 62... ... 62 How Weather Affects the Noise You Hear from Highways Condition Number of Impacts Change from Neutral Neutral 20 – Moderate upwind 10 -10 Strong upwind 10 -10 Moderate downwind 20 0 Strong downwind – – Weak lapse 10 -10 Strong lapse 10 -10 Weak inversion 20 0 Strong inversion 20 0 Note: dashes indicate no data. Source: Bowlby & Associates for NCHRP Project 25-52. Read the entire page →
From page 63... ... Implications for Noise Impact and Abatement 63 Source: Bowlby & Associates for NCHRP Project 25-52. Figure 45. Read the entire page →
From page 64... ... 64 How Weather Affects the Noise You Hear from Highways strong upwind conditions reduce sound levels at the impacted residences by approximately 2 dB, although the sound levels for many of the impacted residences remain above 66 dBA. The number of impacts is reduced from 30 to 22 and 24 for moderate and strong upwind conditions, respectively. Read the entire page →
From page 65... ... Implications for Noise Impact and Abatement 65 Source: Bowlby & Associates for NCHRP Project 25-52. Figure 47. Read the entire page →
From page 66... ... 66 How Weather Affects the Noise You Hear from Highways Specifically, moderate upwind and strong upwind conditions reduce ILs by between 1 dB and 3 dB at both sites. Weak lapse conditions reduce barrier effectiveness by 1 dB to 2 dB at Site #1 and 1 dB to 3 dB at Site #2, while strong lapse conditions reduce ILs by 1 dB at Site #1 and 0 dB to 1 dB at Site #2. Read the entire page →
From page 67... ... Implications for Noise Impact and Abatement 67 Reasonableness For a noise barrier to be reasonable, the following conditions must be met: • The barrier must meet the NRDG in the SHA's noise policy. • The barrier must be cost-effective in accordance with the SHA noise policy. Read the entire page →
From page 68... ... 68 How Weather Affects the Noise You Hear from Highways Source: Bowlby & Associates for NCHRP Project 25-52. Figure 49. Read the entire page →
From page 69... ... Implications for Noise Impact and Abatement 69 residences. As with Site #1, moderate upwind, strong upwind, weak lapse, and strong lapse conditions reduce ILs at many residences, resulting in significant reductions in the number of benefited residences. Read the entire page →
From page 70... ... 70 How Weather Affects the Noise You Hear from Highways and a cost-effectiveness analysis is not completed. As shown in Figure 52, for Site #2, the APBR is 334 sf (barrier area of 16,038 sf divided by 44 benefited residences) Read the entire page →
From page 71... ... Implications for Noise Impact and Abatement 71 N/A N/A N/A Source: Bowlby & Associates for NCHRP Project 25-52. Figure 52. Read the entire page →
From page 72... ... 72 How Weather Affects the Noise You Hear from Highways Frequency of Meteorological Conditions The frequency and duration of the various meteorological conditions might also be a key factor to consider. Neutral conditions may rarely occur in areas where windy conditions are typical throughout the year. Read the entire page →
From page 73... ... Implications for Noise Impact and Abatement 73 Strong winds are not typical at the location and there is no clear prevailing condition during the day (S1, S2, and S3) Read the entire page →

From page 58...

... 58 The state of the practice in the United States is to model sound levels, evaluate noise impacts, and design noise abatement measures under neutral meteorological conditions (no wind or temperature effects)