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From page 49... ... 49 C H A P T E R 7 7.1 Research Approach 7.1.1 Basic Concepts A row of small buildings such as the detached houses in Figure 33 acts as a series of small noise barriers with gaps in between them, which reduces sound levels at receivers behind the row. In FHWA TNM 2.5, one could choose to model each house as a barrier object. Read the entire page →
From page 50... ... 50 building row, with other building rows simply adding 1.5 dB attenuation per 1⁄3 octave band. Nonetheless, the FHWA TNM building row object is a very important parameter in noise impact assessment, affecting how quickly sound levels drop off with distance from the road. Read the entire page →
From page 51... ... 51 7.2 Outcome of the Research -- Best Practices and How to Implement Them for a Noise Study or TNM 7.2.1 Distance from Building Rows and Percentage of Blockage The results showed the following: • As the distance from the building row (and the roadway) increases, the amount of noise reduction decreases. Read the entire page →
From page 52... ... 52 Distance to Building Row, ft Noise Reduction Differences between Different Building Percentages, dB 20% 30% 40% 50% 60% 70% 80% Building Row Height Change from 20 ft to 25 ft 10 0.0 0.0 −0.1 −0.1 −0.1 −0.2 −0.3 30 −0.1 0.0 −0.2 −0.2 −0.2 −0.3 −0.5 50 −0.1 −0.1 −0.2 −0.3 −0.5 −0.7 −0.9 70 −0.2 −0.2 −0.2 −0.4 −0.5 −0.7 −1.0 90 −0.1 −0.2 −0.3 −0.5 −0.6 −0.8 −1.2 110 −0.2 −0.3 −0.3 −0.5 −0.6 −0.9 −1.2 130 −0.2 −0.2 −0.4 −0.5 −0.8 −1.0 −1.4 170 −0.2 −0.3 −0.5 −0.7 −1.0 −1.4 −1.7 210 −0.3 −0.4 −0.6 −0.8 −1.1 −1.4 −1.8 250 −0.3 −0.4 −0.6 −0.8 −1.1 −1.4 −1.8 290 −0.2 −0.4 −0.6 −0.8 −1.1 −1.3 −1.7 330 −0.2 −0.4 −0.6 −0.8 −1.0 −1.3 −1.6 430 −0.3 −0.3 −0.5 −0.7 -0.9 −1.1 −1.3 530 −0.2 −0.3 −0.5 −0.6 −0.8 −1.0 −1.3 730 −0.2 −0.4 −0.5 −0.7 −0.9 −1.0 −1.3 930 −0.2 −0.4 −0.5 −0.6 −0.8 −1.0 −1.2 Building Row Height Change from 25 ft to 30 ft 10 0.0 −0.1 0.0 0.0 0.0 0.0 −0.1 30 0.0 −0.1 0.0 0.0 −0.1 −0.2 −0.2 50 0.0 −0.1 −0.1 −0.1 −0.1 −0.2 −0.3 70 0.0 0.0 −0.1 −0.1 −0.2 −0.3 −0.5 90 0.0 0.0 −0.1 −0.1 −0.2 −0.3 −0.5 110 0.0 0.0 −0.1 −0.2 −0.3 −0.4 −0.7 130 0.0 −0.1 −0.2 −0.3 −0.3 −0.6 −0.8 170 −0.1 −0.2 −0.2 −0.3 −0.4 −0.6 −0.9 210 −0.1 −0.1 −0.2 −0.3 −0.5 −0.6 −0.9 250 −0.1 −0.1 −0.2 −0.4 −0.5 −0.7 −1.0 290 −0.2 −0.2 −0.2 −0.4 −0.5 −0.8 −1.1 330 −0.1 −0.2 −0.3 −0.4 −0.6 −0.8 −1.1 430 −0.1 −0.3 −0.4 −0.5 −0.7 −1.0 −1.3 530 −0.2 −0.3 −0.4 −0.6 −0.8 −1.0 −1.3 730 −0.2 −0.2 −0.4 −0.5 −0.7 −1.0 −1.3 930 −0.1 −0.2 −0.3 −0.5 −0.7 −0.9 −1.2 Building Row Height Change from 20 ft to 30 ft 10 0.0 −0.1 −0.1 −0.1 −0.1 −0.2 −0.4 30 −0.1 −0.1 −0.2 −0.2 −0.3 −0.5 −0.7 50 −0.1 −0.2 −0.3 −0.4 −0.6 −0.9 −1.2 70 −0.2 −0.2 −0.3 −0.5 −0.7 −1.0 −1.5 90 −0.1 −0.2 −0.4 −0.6 −0.8 −1.1 −1.7 110 −0.2 −0.3 −0.4 −0.7 −0.9 −1.3 −1.9 130 −0.2 −0.3 −0.6 −0.8 −1.1 −1.6 −2.2 170 −0.3 −0.5 −0.7 −1.0 −1.4 −2.0 −2.6 210 −0.4 −0.5 −0.8 −1.1 −1.6 −2.0 −2.7 250 −0.4 −0.5 −0.8 −1.2 −1.6 −2.1 −2.8 290 −0.4 −0.6 −0.8 −1.2 −1.6 −2.1 −2.8 330 −0.3 −0.6 −0.9 −1.2 −1.6 −2.1 −2.7 430 −0.4 −0.6 −0.9 −1.2 −1.6 −2.1 −2.6 530 −0.4 −0.6 −0.9 −1.2 −1.6 −2.0 −2.6 730 −0.4 −0.6 −0.9 −1.2 −1.6 −2.0 −2.6 930 −0.3 −0.6 −0.8 −1.1 −1.5 −1.9 −2.4 Table 9. Change in noise reduction behind a single building row as a function of building height for different building percentages. Read the entire page →
From page 53... ... 53 -1 0 1 2 3 4 5 6 7 0 100 200 300 400 500 600 700 800 900 1000 Di ffe re nc e i n L A eq 1h fr om 0 % ca se , d B Distance from edge of near travel lane, 20% blockage 30% blockage 40% blockage 50% blockage 60% blockage 70% blockage 80% blockage Figure 34. Noise reduction as a function of building percentage for a single 20-ft-high building row 70 ft from edge of an eight-lane roadway. Read the entire page →
From page 54... ... 54 Distance Behind Building Row, ft Noise Reduction Differences between Different Building Percentages, dB From 20 to 30% From 30 to 40% From 40 to 50% From 50 to 60% From 60 to 70% From 70 to 80% Building Row Height of 20 ft 10 0.5 0.6 0.8 0.9 1.1 1.5 30 0.6 0.5 0.7 0.8 1.0 1.3 50 0.5 0.5 0.6 0.7 0.8 1.1 70 0.5 0.5 0.5 0.7 0.7 0.9 90 0.4 0.4 0.5 0.6 0.7 0.7 110 0.4 0.5 0.4 0.6 0.5 0.7 130 0.4 0.3 0.5 0.4 0.5 0.5 170 0.3 0.3 0.3 0.3 0.3 0.4 210 0.3 0.2 0.3 0.2 0.3 0.2 250 0.3 0.2 0.2 0.2 0.2 0.1 290 0.2 0.2 0.2 0.1 0.2 0.0 330 0.2 0.1 0.2 0.1 0.1 0.1 430 0.2 0.1 0.1 0.1 0.0 0.0 530 0.2 0.1 0.1 0.0 0.0 −0.1 730 0.1 0.1 0.0 0.0 0.0 −0.2 930 0.0 0.1 0.0 −0.1 −0.1 −0.3 Building Row Height of 25 ft 10 0.5 0.7 0.8 0.9 1.2 1.6 30 0.5 0.7 0.7 0.8 1.1 1.5 50 0.5 0.6 0.7 0.9 1.0 1.3 70 0.5 0.5 0.7 0.8 0.9 1.2 90 0.5 0.5 0.7 0.7 0.9 1.1 110 0.5 0.5 0.6 0.7 0.8 1.0 130 0.4 0.5 0.6 0.7 0.7 0.9 170 0.4 0.5 0.5 0.6 0.7 0.7 210 0.4 0.4 0.5 0.5 0.6 0.6 250 0.4 0.4 0.4 0.5 0.5 0.5 290 0.4 0.4 0.4 0.4 0.4 0.4 330 0.4 0.3 0.4 0.3 0.4 0.4 430 0.2 0.3 0.3 0.3 0.2 0.2 530 0.3 0.3 0.2 0.2 0.2 0.2 730 0.3 0.2 0.2 0.2 0.1 0.1 930 0.2 0.2 0.1 0.1 0.1 −0.1 Building Row Height of 30 ft 10 0.6 0.6 0.8 0.9 1.2 1.7 30 0.6 0.6 0.7 0.9 1.2 1.5 50 0.6 0.6 0.7 0.9 1.1 1.4 70 0.5 0.6 0.7 0.9 1.0 1.4 90 0.5 0.6 0.7 0.8 1.0 1.3 110 0.5 0.6 0.7 0.8 0.9 1.3 130 0.5 0.6 0.7 0.7 1.0 1.1 170 0.5 0.5 0.6 0.7 0.9 1.0 210 0.4 0.5 0.6 0.7 0.7 0.9 250 0.4 0.5 0.6 0.6 0.7 0.8 290 0.4 0.4 0.6 0.5 0.7 0.7 330 0.5 0.4 0.5 0.5 0.6 0.7 430 0.4 0.4 0.4 0.5 0.5 0.5 530 0.4 0.4 0.4 0.4 0.4 0.5 730 0.3 0.4 0.3 0.4 0.4 0.4 930 0.3 0.3 0.3 0.3 0.3 0.2 Table 10. Changes in noise reduction for 10% changes in building percentages for a single building row. Read the entire page →
From page 55... ... 55 behind the building row. For a difference of less than 0.5 dB, the needed distance behind the building row is a function of building row height: • 20 ft high -- beyond 130 ft behind the building row. Read the entire page →
From page 56... ... 56 For two building rows, the noise reductions are sensitive to building row height as the distance back from the second row increases. Close in behind the second row, the differences in noise reduction are generally small for the different heights except for the high building percentages. Read the entire page →
From page 57... ... 57 -1 0 1 2 3 4 5 6 7 0 100 200 300 400 500 600 700 800 900 1000 Di ffe re nc e in L A eq 1h fr om 0 % c as e, d B Distance from edge of near travel lane, 20% blockage 30% blockage 40% blockage 50% blockage 60% blockage 70% blockage 80% blockage Figure 39. Noise reduction as a function of building percentage for three 20-ft-high building rows near a single 12-ft-wide roadway. Read the entire page →
From page 58... ... 58 the two-row case is present: the noise reduction decreasing with increasing distance from the first building row. The noise reduction then steps back up for receivers behind the second row, and then decays again with increasing distance from the second row until it steps back up again for receivers behind the third row. Read the entire page →
From page 59... ... 59 The other cases are in Appendix F and show similar effects on both the with-barrier and no-barrier levels and the resultant overall noise reductions. 7.2.5 Building Rows Perpendicular to the Roadway Rows of houses can also be perpendicular to the highway -- along streets that end at the highway right-of-way, in a cul-de-sac, or intersecting with a collector road that is parallel and adjacent to the highway. Read the entire page →
From page 60... ... 60 Figure 42. FHWA TNM plan view of four perpendicular building rows adjacent to an eight-lane highway. Read the entire page →
From page 61... ... 61 shows the corresponding Maryland State Highway Administration modeling of the houses as building barriers on the right and the comparative modeling of the houses as FHWA TNM building rows on the left. In the case shown in Figure 44, the analyst chose to model three sides of each house as barrier segments. Read the entire page →
From page 62... ... 62 7.2.6.1 Case Study Comparisons of Measured and Modeled Data For this analysis, five different projects with a total of eight noise study areas were examined for a comparison between modeling detached houses using building rows and modeling using building barriers. Sound-level measurement results with concurrent traffic counts were available. Read the entire page →
From page 63... ... 63 This effect was tested using four FHWA TNM runs based on three of the modeled sites from the analysis of modeling houses as building rows versus modeling them as building barriers. Figure 45 shows two of the tested cases, with one set of receivers (labeled 1 through 7) Read the entire page →
From page 64... ... 64 Figure 46. FHWA TNM plan view (top) Read the entire page →

From page 49...

... 49 C H A P T E R 7 7.1 Research Approach 7.1.1 Basic Concepts A row of small buildings such as the detached houses in Figure 33 acts as a series of small noise barriers with gaps in between them, which reduces sound levels at receivers behind the row. In FHWA TNM 2.5, one could choose to model each house as a barrier object.