Field Evaluation of Reflected Noise from a Single Noise Barrier—Phase 1 (2016) / Chapter Skim
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A - ii C O N T E N T S Introduction to Appendix A ...................................................................................................................... A-3 Community noise issues that have led to investigations of noise reflected from barriers ......................
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A - 1 E X E C U T I V E S U M M A R Y , A P P E N D I X A This Appendix was prepared as a Technical Memorandum in fulfillment of Task No. 2, "Literature Review," for NCHRP Research Project 25-44, "Field Evaluation of Reflected Noise from a Single, Reflective Noise Barrier." The literature review addresses the community noise issues that have led to investigations of noise reflected from barriers, past attempts to quantify the magnitude and effects of noise reflected from barriers, and the success of efforts to reduce noise reflected from barriers.
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A - 2 The success of efforts to reduce noise reflected from barriers has varied across the U.S., in part due to the different approaches pursued by various state highway agencies. While some state DOTs have responded to community concerns about reflected sound by conducting investigations attempting to document perceived increases in noise, other DOTs have addressed similar concerns by adding soundabsorptive materials to barriers after construction.
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A - 3 C H A P T E R A - 1 Introduction to Appendix A This Technical Memorandum has been prepared in fulfillment of Task No. 2, "Literature Review," for NCHRP Research Project 25-44, "Field Evaluation of Reflected Noise from a Single Noise Barrier." The goal of this task is to conduct a review of available literature on reflected noise from single noise barriers addressing the following: • The community noise issues that have led to investigations of noise reflected from barriers, • Past attempts to quantify the magnitude and effects of noise reflected from barriers, and • The success of efforts to reduce noise reflected from barriers.
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A - 4 C H A P T E R A - 2 Community noise issues that have led to investigations of noise reflected from barriers Overview Community noise issues that have led to the investigations of noise reflected from barriers date back almost as long as the first widespread construction of highway noise barriers in the U.S.
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A - 5 noise source followed by an abrupt change, spectral changes in sound due to reflections, or alteration of the temporal characteristics of vehicle passbys.12 The California Department of Transportation (Caltrans) , one of the leaders in constructing noise barriers for nearly four decades, has received and responded to complaints of reflected sound for almost as long.
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A - 6 Washington State DOT (WSDOT) also has received complaints regarding noise barrier reflections, but is restricted in its ability to respond in-person to all complaints due to staff time limitations.
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A - 7 threshold of perception for reflected noise." 25 The authors note that "as far back as the late 1940s, experiments confirmed that over 50% of listeners demonstrated sensitivity to changes in levels of broadband noise of less than 0.5 dB." 26 (See the following summary in Section 0.) Although "conventional wisdom holds that small differences in sound levels are more difficult to perceive in environmental rather than laboratory settings," the paper contends that other factors may influence listeners' perceptions and sensitivities, increasing the likelihood both that they will notice changes and perceive the changes as increases in level attributed to reflections from a new noise barrier: • Long-term exposure to a particular noise source such as a nearby highway may lead to ingrained expectations regarding typical noise levels and heighten sensitivity to even small changes.
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From page 127... ...
A - 8 some cases, considerably above the road. Based on their measurements, the researchers concluded that "reflected noise from the walls is not significant." Although modeling exercises indicated that theoretical increases in A-weighted noise levels of up to 2 decibels were possible, the report stated that "changes of 2 to 3 dBA from one day to the next cannot be normally perceived by most people." Results of this study are further described in Section 0.
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A - 9 barrier on the west side of the road. In response, MnDOT conducted a test to determine if construction of the noise barrier had increased noise levels, and if so, the magnitude of the increases.
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A - 10 and could include new noise readings.
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A - 11 Correspondence with Mariano Berrios, Florida Department of Transportation, November 7, 2013 FDOT is not aware of any studies, investigations, or complaints due to noise reflected from highway noise barriers in Florida. In the past, "Florida had a couple of ‘reflection' related complaints but they were unfounded." Noise reflection has not been a significant issue in Florida, therefore they have not done any research/studies in that area.
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A - 12 C H A P T E R A - 3 Past attempts to quantify the magnitude and effects of noise reflected from barriers Overview Over the past several decades, state highway agencies have made numerous attempts to quantify the magnitude and effects of noise reflected from highway noise barriers. In 1978, in response to complaints about increased noise from residents opposite a newly constructed noise barrier along US Route 101 in San Jose, Caltrans performed one of the first investigations of sound reflected from a highway noise barrier.
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A - 13 practical to do these studies on a routine basis because of their high cost, both in terms of money and necessary resources."30 In 1999, Caltrans conducted another measurement program in conjunction with the construction of new noise barriers along Interstate 680 in Alamo, California using the guidelines described above. To evaluate noise level changes, before and after noise levels were grouped into similar meteorological categories and compared.
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A - 14 familiarity with the highway noise source followed by an abrupt change, spectral changes in sound due to reflections, or altering the temporal character of vehicle passbys. 35 Therefore, it is possible that the studies, while accurately quantifying the magnitude of the change in overall sound level due to reflections, were not addressing the effects of reflected noise perceived by residents.
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A - 15 Summaries of Cited Works (Past attempts to quantify the magnitude and effects of noise reflected from barriers) Menge, C.W.
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A - 16 highway, where many complaints had originated. After adding sound-absorptive treatment to the noise barrier opposite the affected community, Caltrans conducted follow-up measurements.
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A - 17 URS Greiner Woodward Clyde and Illingworth and Rodkin, Inc., Interstate 680 in Contra Costa County, Pre- and Post Sound Wall Noise Study – Stone-Kemline Sound Walls, Near Stone Valley Road, June 1999 This report evaluated noise conditions before and after construction of new noise barriers along Interstate 680 in Alamo, California. The measurement program was designed to quantify any differences in noise levels "before" and "after" the installation of the noise barriers at locations relatively distant from the freeway traffic noise source.
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A - 18 before/after traffic noise levels were normalized to account for differences in traffic using FHWA's STAMINA 2.0 traffic noise prediction model. The analysis found with a 95% confidence level that the noise barrier did not cause a statistically significant difference in overall A-weighted L10 sound levels at three of the four measurement sites.
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A - 19 The RFP indicated that a comprehensive research plan should be developed to address this topic as follows: Perform noise measurements on sound absorptive concrete walls vs. reflective concrete walls to determine if there is a discernable difference at the receptor and noise sensitive areas opposite the freeway.
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A - 20 McNerney, Michael, S.M. Bucsak, E.J.
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A - 21 C H A P T E R A - 4 The success of efforts to reduce noise reflected from barriers Overview The success of efforts to reduce noise reflected from barriers has varied across the U.S., in part due to the different approaches pursued by various state highway agencies. As described in Section 0, some DOTs have responded to community concerns about sound reflected from noise barriers by conducting investigations to attempt documenting perceived increases in noise.
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A - 22 • In its Environmental Procedures Manual, Tennessee DOT (TDOT) acknowledges that "noise reflections off of a noise barrier on one side of a highway can .
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A - 23 would be less (1 to 2-1/2 dB) at closer receptors.51 This project involved parallel barriers, but some of the finding are relevant to measurement studies of single-barrier reflections.
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A - 24 Correspondence with Chris Blaney, Ontario Ministry of Transportation, November 4, 2013 The Ontario Ministry of Transportation (MTO) provides an example of an agency with a long-standing policy of using sound-absorptive barriers to reduce or eliminate the effects of reflected noise.
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A - 25 Tennessee Department of Transportation Environmental Procedures Manual, Guidelines for Preparing Environmental Documents for Federally Funded and State Funded Transportation Projects, Section 5.3.4.10 "Final Noise Barrier Design," Spring 2011 In its Environmental Procedures Manual, TDOT provides guidance for use of sound absorptive noise barrier materials. In the case of parallel barriers, TDOT requires a detailed noise reflections analysis using TNM's "Parallel Barriers" module.
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A - 26 1.1.1 Virginia Department of Transportation Highway Traffic Noise Impact Analysis Guidance Manual (Version 4) , Section 10.4 "Applications for Absorptive Noise Barriers," August 6, 2013, p.
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A - 27 median retaining wall and noise barrier then were covered with sound-absorbing panels and barrier insertion loss was measured to be 5 dB, sufficient to be considered effective. The authors note that this is an example of where an "imperceptible" one- to two-decibel change makes the difference between an ineffective and effective barrier.
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From page 147... ...
A - 28 influence of the new barrier reflection was greater and less consistent, with second-row receivers receiving a predicted average 4.3 dBA increase versus an average 2.6 dBA increase for first-row receivers. The analysis indicated the largest increases for those receiver locations with direct line of sight to the new barrier.
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A - 29 C H A P T E R A - 5 Conclusions for Appendix A This review of available literature regarding reflected noise from single, reflective barriers has focused on (1) the community noise issues that have led to investigations of noise reflected from barriers, (2)
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A - 30 R E F E R E N C E S Berrios, M Florida Department of Transportation.
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A - 31 Ohio Department of Transportation. Highway Traffic Noise Analysis Manual, Analysis and Abatement of Traffic Noise.
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