National Academies Press: OpenBook

Field Evaluation of Reflected Noise from a Single Noise Barrier (2018)

Chapter: Appendix D - Using the Barrier Reflections Screening Tool

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Suggested Citation:"Appendix D - Using the Barrier Reflections Screening Tool." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix D - Using the Barrier Reflections Screening Tool." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix D - Using the Barrier Reflections Screening Tool." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix D - Using the Barrier Reflections Screening Tool." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix D - Using the Barrier Reflections Screening Tool." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix D - Using the Barrier Reflections Screening Tool." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix D - Using the Barrier Reflections Screening Tool." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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Suggested Citation:"Appendix D - Using the Barrier Reflections Screening Tool." National Academies of Sciences, Engineering, and Medicine. 2018. Field Evaluation of Reflected Noise from a Single Noise Barrier. Washington, DC: The National Academies Press. doi: 10.17226/25297.
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D-3 C H A P T E R D - 1 Intended Use The accompanying Barrier Reflections Screening Tool quickly estimates the expected increase in traffic noise due to reflections from a barrier on the opposite side of the road. This tool focuses on a single variable to estimate the barrier-reflected noise effect at receptors opposite a noise barrier: path-length difference (comparing the path length for direct sound and for barrier-reflected sound). The tool uses this variable to conservatively estimate the increase in traffic noise based on the geometrical spreading of sound from a line source. The results can be used to determine areas where detailed evaluation of reflected noise and abatement options should be considered. Analysts should carefully define inputs, and results should be considered within the context of each individual scenario to ensure that values are relevant. For instance, the increase in noise levels from barrier reflections may not contribute to the overall sound level if background noise levels at the receptor are dominated by a source other than traffic on the highway being evaluated. This may be the case if local roads or other noise sources are 10 dB greater than the traffic noise. It is also recognized that variables other than path length difference, such as meteorological or ground effects, contribute to the barrier reflections effect. Depending on the amount of those contributions, estimates for other variables may need to be combined with the path-length screening tool to refine results.

D-4 C H A P T E R D - 2 Instructions for Use Two versions of the tool (separated by tabs in the spreadsheet file) are provided, and they accept different input types. To estimate the barrier reflections effects, use the “based on distances” tab if the direct path length is known, and the “based on coordinates” tab if XYZ coordinate locations of the source, receptor, and barrier are known. It is recommended to use the centerline of all traffic lanes as the traffic noise source location. This will provide an approximation of the barrier reflection contribution for all lanes of traffic. For typical highways, this will be the center of the median; however, depending on the number of lanes in each direction and inside shoulder widths, the centerline may shift closer to the receptor or barrier. Barrier reflection effects can be estimated for individual traffic lanes by choosing that lane as a source location. In both versions of the tool, cells shaded blue require a user input, cells shaded yellow allow for optional user input, and the cell shaded green provides the result. The dynamic graph in each tab provides a bird’s- eye view of the setup and can be used to visually verify that input values match expectations. Optional input allows for including shielding effects for both the direct and reflected sound levels. User- estimated shielding can be entered if there are features in the site geometry that potentially block or partially block the line of sight from the source to receptor or barrier to receptor. Such features could include the edge of pavement for a cut roadway, edge of an elevated roadway, or safety barriers with heights greater than a standard 32-inch safety barrier. Optional input also allows for determining the effect of barrier reflections for traffic upstream or downstream. Some receptors do not have a noise barrier directly across the highway; however, they may experience effects from upstream or downstream noise barriers. In such cases, a source offset can be applied to evaluate the effect of those barriers. Care should be taken when considering an offset. In cases with a large offset, the direct path noise at the point of closest approach to the receptor (the zero offset location) may be higher than the offset direct path noise plus the reflected increase. In such cases, although the barrier is causing an increase in sound levels from the offset position, the sound increase at the receptor due to all sources (including the zero offset location) may be negligible.

D-5 C H A P T E R D - 3 Validation of Estimates For NCHRP Project 25-44 Phase 1, the project team conducted field measurements in California (SR-71), Maryland (MD-5), Tennessee (I-24 & Briley Parkway), and Illinois (I-90). For Phase 2, the project team conducted field measurements in Ohio at three sites: I-75, I-70, and I-270. Detailed information about the measurements can be found in Appendix E, which is available for download from the NCHRP Research Report 886 web page at www.trb.org. The analysis found the measured barrier effect (comparing sites with and without a barrier) for each location. For validating the screening tool, the tool results are compared to both A-weighted and unweighted measured results. The unweighted results provide a conservative estimate of the barrier reflection effects (generally slightly greater effect than for A-weighted results). For locations where two microphones were placed the same distance from the barrier, the selected range came from the microphone with the higher elevation. Since the influence from ground effects are not considered in the screening tool, the higher microphone provides for a more accurate comparison. The estimated effect (from the screening tool) is presented in Figure 1, shown as circles. The estimated effect is compared to the range of measured barrier reflection effects, both unweighted (diamonds) and A-weighted (squares). The distances listed for each site represent the perpendicular distance from the traffic centerline to the receivers. Three of the measured locations (I-24, Briley Parkway, and I-75) included a median barrier of a height higher than a typical safety barrier. In these cases, it was assumed that the barrier provided no direct path shielding (either from the source to the receptor or the source to the noise barrier) because reflections off the median barrier from the near lanes of travel can be considered roughly equivalent to the direct path noise from the far lanes from cases without a barrier. However, the taller barrier does provide some shielding of the reflected noise, so a shielding amount of 2 dB was included in the screening tool estimates for these sites. For site I-270, a slightly modified version of the screening tool was used to estimate the effect of reflections from the homes behind the microphone locations. The effect was applied to the measured data to compare it to screening tool estimates. An additional plot is shown in Figure 2 to illustrate the relationship of the maximum measured barrier reflections effect as a function of reflected path length, which appears to be a key parameter in the magnitude of the effect. Several parameters were examined, and this parameter helps to differentiate absorptive barrier sites. Key observations of the validation analysis results in Figure 1 and Figure 2 are as follows: All the estimated values fall within or slightly above the top of the measured value ranges. This indicates that the screening tool provides a conservative estimate of the barrier-reflected effect and is appropriate for use in screening for potential adverse effects due to a noise barrier on the opposite side of a highway. The barrier effect appears to be dominated by path lengths. Any trends related to barrier absorption are likely masked. It could be expected that the screening tool would over-estimate

D-6 the barrier effect for absorptive barriers (sites I-75, I-70, and I-270), but since the absorptive barrier sites all had geometries with fairly large propagation distances for the reflected path, that expectation is not realized. Figure 1. Estimated barrier effect compared to unweighted and A-weighted results. Figure 2. Maximum measured barrier effect compared to reflected path length. -2 -1 0 1 2 3 4 5 SR-71 (72ft) SR-71 (447ft) MD-5 (122ft) I-24 (137ft) Briley Pkwy (129ft) I-90 (114ft) I-90 (138ft) I-70 (141ft) I-75 (155 ft) I-75 (105 ft) I-270 (178 ft) I-270 (97 ft) Ch an ge in n oi se d ue to b ar ri er (d B) Measurement Location Measured unweighted effect range (dB) Measured A-weighted effect range (dBA) Estimated effect (dB) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 100 200 300 400 500 600 700 M ea su re d M ax im um In cr ea se (d B) Reflected Distance (ft) Reflective Barriers Absorptive Barriers A-wt Reflective Barriers A-wt Absorptive Barriers

Content Available Online The following files are available online for viewing or download. To access these files, go to www.trb.org and search for “NCHRP Research Report 886”. • Appendix D: Using the Barrier Reflections Screening Tool (a PDF copy of this appendix); • Appendix E: NCHRP Project 25-44, Phase 1 (Sound-Reflecting Barriers)—Detailed Protocols and Results (in PDF); • Appendix F: Photographs from NCHRP Project 25-44, Phase 1 (Sound-Reflecting Barriers) Measurement Sites (in PDF); • Appendix G: Photographs from NCHRP Project 25-44, Phase 2 (Sound-Absorbing Barriers) Measurement Sites (in PDF); • The Barrier Reflections Screening Tool (provided as a spreadsheet file); and • “Reflected Sound from Highway Noise Barriers” (the customizable layperson’s guide, provided in Word). A presentation file that summarizes the research also is available for viewing or dowload from the NCHRP 25-44 project page. Some of these files are very large and will take some time to download.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation

TRA N SPO RTATIO N RESEA RCH BO A RD 500 Fifth Street, N W W ashington, D C 20001 A D D RESS SERV ICE REQ U ESTED ISBN 978-0-309-39067-5 9 7 8 0 3 0 9 3 9 0 6 7 5 9 0 0 0 0 Field Evaluation of Reflected N oise from a Single N oise Barrier N CH RP Research Report 886 TRB

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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 886: Field Evaluation of Reflected Noise from a Single Noise Barrier analyzes the characteristics of sound reflected from a noise barrier to the opposite side of a highway. State departments of transportation (DOTs) periodically receive complaints from residents about increases in traffic noise that residents believe are the result of noise reflected from a new noise barrier added across the roadway from them. Currently available analytical tools are limited in their ability to evaluate reflected noise and some of the subtle changes in the quality of sound that can occur when it is reflected. Therefore, it is a challenge for DOTs to determine conclusively if complaints about reflected noise are the result of actual or perceived changes in noise characteristics, and to identify locations where absorptive surface treatments could be beneficial.

The study compares reflected noise from sound-reflecting barriers and from barriers with a sound-absorptive surface. It examines both the levels and frequencies of reflected noise to better understand how reflected noise is experienced by communities.

The full report, which includes four detailed appendices, is 27 MB and may take time to download. It is accompanied by several appendices, a tool, and a guide:

A presentation file that summarizes the research also is available on the report project page.

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