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

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

A-3 S U M M A R Y Literature Review This appendix presents the literature review conducted for NCHRP Project 25-44, “Field Evaluation of Reflected Noise from a Single Noise Barrier.” It 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. Community noise issues that have led to the investigations of noise reflected from barriers nearly date back to the first widespread construction of U.S. highway noise barriers in the 1970s. With a noise barrier on only one side of a highway, reflected sound typically may increase the overall noise level at a receptor opposite the barrier by 1 to 2 decibels (dB). While this change generally has been considered too small to be readily perceived,1 state highway agencies nonetheless have received complaints of increased noise from residents following the construction of reflective noise barriers, including threats of legal action and petitions to have noise barriers removed. 2 As a result of such reactions, some state departments of transportation (DOTs) have invested considerable effort and money researching the magnitude of sound level increases from reflective noise barriers along highways.3 Other state DOTs, despite the widespread construction of reflective noise barriers, either have had few community complaints due to reflected sound, or have been able to resolve any such issues without extensive investigations. During this same period there have been numerous attempts to quantify the magnitude and effects of noise reflected from barriers. Although some studies have identified increases in overall A-weighted sound level of 0 to 3 dB because of reflections, investigators typically concluded that such changes were insignificant and not perceptible to the human ear. These conclusions were based in part on guidance issued both by the Federal Highway Administration (FHWA) and by state highway agencies.4 Yet despite study conclusions indicating that increases in noise levels were so small that they should have been imperceptible, in many cases people did respond to reflected sound, or at least to the perception of it. One potential difficulty is that many of the studies focused on the change in the overall sound level; the changes that residents perceived, however, may have been related to more than a simple increase in the overall sound level. Factors other than a change in overall noise levels may increase the likelihood both that listeners will notice changes and perceive the changes as increases attributed to reflections from a new noise barrier. Such factors may include long-term familiarity with the highway noise source followed by an abrupt change, spectral changes in traffic noise due to reflections, or alterations of the temporal characteristics of 1 Federal Highway Administration, Highway Traffic Noise: Analysis and Abatement Guidance, FHWA-HEP-10- 025, December 2011, p. 60. 2 For example: Hendriks, R. and J. Hecker, Parallel Noise Barrier Report: A Noise Absorptive Demonstration Project, San Diego Freeway (I-405), Los Angeles, CA, Caltrans District 7, Environmental Investigations Section, July 1989. 3 Menge, C.W. and D.E. Barrett. “Reflections from Highway Noise Barriers and the Use of Absorptive Materials in the United States: Why Small Increases in Noise Levels May Deserve Serious Consideration,” Transportation Research Record: Journal of the Transportation Research Board, No. 2233, Transportation Research Board of the National Academies, Washington, D.C., 2011, p. 161. 4 For example: Federal Highway Administration, Highway Traffic Noise: Analysis and Abatement Guidance, p. 60. Also: Hendriks, R., General Guidelines for Studying the Effects of Noise Barriers on Distant Receivers, Technical Advisory TAN-89-01-R9701, California Department of Transportation, November 30, 1998, p. 7.

A-4 vehicle pass-bys.5 Recently, studies have begun to examine further influences that may be perceived by residents in addition to changes in the A-weighted sound level. The success of efforts to reduce noise reflected from barriers has varied across the United States, 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 sound- absorptive materials to barriers after construction. Still others have long-standing practices of installing noise barriers with absorptive surfaces where there is noise-sensitive land use on the opposite side of the highway. Since 2010, FHWA has required state highway agencies to include provisions in their state noise policies for use of absorptive treatment on roadside structures, including noise barriers, retaining walls, bridges, and any other structure the highway agency may consider for application of a sound-absorptive material.6 In response to this requirement, some states have adopted formal policies requiring absorptive treatment on noise barriers in certain situations. Recent investigations in states including California, Minnesota, and Ohio have continued attempts to measure the benefit provided using sound-absorptive noise barrier materials, either on new barriers or as retrofit treatments. 5 Menge and Barrett, op. cit., p. 164. 6 Federal Highway Administration, Highway Traffic Noise: Analysis and Abatement Guidance, p. 60.

A-5 C H A P T E R A - 1 Introduction to Appendix A This appendix reviews available literature on reflected noise from single noise barriers and addressed 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. • The success of efforts to reduce noise reflected from barriers. This appendix is divided into three sections, addressing in turn each of the three topic areas named above. Each section first provides an overview of the topic area, incorporating information from the various relevant reports, papers, and other sources identified during the literature review. Following each overview section, this appendix summarizes relevant material from each of the primary sources. Some of the works cited include information relevant to more than one of the three topic areas. In those cases, related information may be included in more than one section of this appendix, with a note alerting the reader that additional information from the primary document can be found elsewhere. While acknowledging some redundancy, this format is useful for readers desiring both a summary of the entire issue of reflections from single barriers and specific information on any of the three individual topic areas. The primary documents identified during this literature review were gathered from several sources. Many of the documents were provided by state DOT representatives in response to a query from the research team for any relevant studies, investigations, or incidences of complaints due to noise reflected from highway noise barriers in their states. Others were provided by members of the research team based on their many years of collective practice in the field of highway noise, and several of the documents summarized herein previously were identified and discussed in the paper “Reflections from Absorptive Highway Noise Barriers and the Use of Absorptive Materials in the United States.” 7 The research team acknowledges and appreciates the efforts of all who contributed to this literature review. 7 Menge and Barrett, op cit., pp. 161–166.

A-6 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 nearly date back to the first widespread construction of highway noise barriers in the United States in the 1970s. By the end of 2010, over 180 million sq. ft. of highway noise barriers had been constructed in the United States, of which approximately 98% are reflective.8 For many years, on many occasions, and in many different states, communities have complained of sound reflected from highway noise barriers to receptors on the other side of the highway. The problem may occur when the community on one side of a highway qualifies for a barrier but residents on the other side of the highway, for one reason or another, do not qualify. The concern sometimes is exacerbated by residents who may be impacted by the highway noise yet do not meet certain feasibility or reasonableness criteria for abatement. For them, experiencing a noticeable change in the sound level caused by their neighbors receiving abatement may be further cause for annoyance. When a reflective noise barrier is present on only one side of a highway, common guidance has said that reflected sound typically may increase the overall noise level at a receptor opposite the barrier by 1 to 2 dB. While this change generally has been considered too small to be readily perceived, 9 , 10 state DOTs nonetheless have received complaints from residents opposite reflective barriers following their construction. Researchers have recognized since at least the 1940s that under controlled, laboratory situations, listeners have demonstrated sensitivity to immediate changes in levels of broadband noise of less than 0.5 dB.11 Although conventional wisdom holds that small differences in sound levels are more difficult to perceive in environmental rather than laboratory settings, it also has been suggested that other factors caused by reflected sound 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. These factors may include long-term familiarity with the highway noise source followed by an abrupt change, spectral changes in sound due to reflections, or alteration of the temporal characteristics of vehicle pass-bys.12 8 Federal Highway Administration, Summary of Noise Barriers Constructed by December 31, 2010, FHWA-HEP- 12-044, July 2012. 9 Federal Highway Administration, Fundamentals and Abatement of Highway Traffic Noise: Textbook and Training Course. U.S. Department of Transportation, Sept. 1980. 10 For example: “Attempts to conclusively measure [the increase in sound level due to a single barrier reflection] have rarely show an increase of greater than 1-2 dB(A), an increase that is not perceptible to the average human ear.” Federal Highway Administration, Highway Traffic Noise: Analysis and Abatement Guidance, p. 60. 11 Miller, George A., “Sensitivity to Changes in Intensity of White Noise and Its Relation to Masking and Loudness,” The Journal of the Acoustical Society of America, Volume 19, Number 4, July 1947, p. 609. 12 Menge and Barrett, op. cit., p. 164.

A-7 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 that entire time. As a result of such community reactions, Caltrans and other DOTs have spent considerable effort and money researching the magnitude of sound level increases from reflective noise barriers along highways.13 Since the late 1970s, Caltrans has, for example, responded to complaints of reflected sound in various locations including San Jose, Los Angeles, Alamo, Oakland, and San Rafael.14 Other state DOTs that have conducted investigations of reflected sound in response to community noise issues include Colorado15 and Minnesota.16,17 In a recent instance of community noise issues leading to an investigation of reflected sound, residents of San Clemente, California, began to complain of increased noise levels shortly after a 16-ft high reflective noise barrier was constructed in 2011 on the opposite side of Interstate 5. The residents claimed that Caltrans had “failed to comply with the California Environmental Quality Act (CEQA) by not adequately notifying residents on both sides of the freeway when it solicited neighborhood input about putting up the new walls.” Even while affirming the legality of the disputed noise barrier, Caltrans offered to work with city and county officials to study the project further, possibly including new noise measurements, and to consider changes.18 Other state DOTs, despite the widespread construction of reflective noise barriers, either have received few community complaints due to reflected sound, or have been able to resolve any such issues without extensive investigations. The Florida Department of Transportation (FDOT), despite having constructed over 150 miles of noise barriers since the 1980s,19 is not aware of any studies, investigations, or recent complaints due to noise reflected from highway noise barriers in Florida. Because reflected noise has not been a significant issue in Florida, FDOT has not conducted any research or studies of the issue.20 The New Hampshire Department of Transportation (NHDOT) acknowledges having received “a few complaints here and there,” but was “able to dismiss those mostly by taking measurements and finding that the noise levels were still below the [Noise Abatement Criteria]21 or that the neighborhood lacked a Type I22 project.” To date, NHDOT has not conducted any studies regarding reflected noise.23 Washington State DOT (WSDOT) also has received complaints regarding noise barrier reflections, but the agency is restricted in its ability to respond in person to all complaints due to staff time limitations. WSDOT has decided not to conduct 13 Ibid., p. 161. 14 Ibid., pp. 162–163. 15 Hankard Engineering, North End Neighborhood Noise Study (Colorado Springs), 2000. 16 Roseen, M., Effects of noise wall located on the East side of TH 100 on noise levels of residences on the Westside of TH 100 in the vicinity of Vernon Avenue, Minnesota DOT, Environmental Analysis and Compliance Section, Environmental Modeling and Testing Unit, January 22, 2002. 17 Roseen, M., Effects of a noise barrier, located on the west side of TH 47 (University Ave.), on the noise levels of residences on the east side of TH 47 located between 45th Ave. N. and 52nd Ave. N., Minnesota DOT, Environmental Analysis and Compliance Section, Environmental Modeling and Testing Unit, September 20, 2002. 18 Shyong, F., “Caltrans offers to consider changes to I-5 sound wall.” Orange County Register, February 3, 2012, updated August 21, 2013. 19 Federal Highway Administration, Summary of Noise Barriers Constructed by December 31, 2010. 20 Berrios, Mariano, Florida Department of Transportation. Message to Douglas Barrett. November 7, 2013. E-mail. 21 The Noise Abatement Criteria (NAC) are the threshold sound levels for each relevant land use type that would require consideration of noise abatement measures on Type I projects. 22 “Type I” projects include either (1) the construction of a highway on a new location or (2) improvements to an existing facility that include substantial horizontal or vertical alteration, the addition of through traffic lanes, the addition of an auxiliary lane (except for when the auxiliary lane is a turn lane), the addition or relocation of interchange lanes or ramps added to a quadrant to complete an existing partial interchange, restriping existing pavement for the purpose of adding a through-traffic lane or an auxiliary lane, or the addition of a new or substantial alteration of a weigh station, rest stop, ride-share lot or toll plaza. (U.S. Code of Federal Regulations, Title 23: Highways - Part 772: Procedures for Abatement of Highway Noise and Construction Noise, June 2010.) 23 Evans, Jonathan, New Hampshire Department of Transportation. Message to Douglas Barrett. Nov. 1, 2013. E-mail.

A-8 detailed investigations because “these situations have fallen outside of their policy guidelines” and also because of “their lack of a funding mechanism to provide additional mitigation.”24 Summaries of Cited Works (Community noise issues that have led to investigations of noise reflected from barriers) Menge, C.W. and D.E. Barrett. “Reflections from Highway Noise Barriers and the Use of Absorptive Materials in the United States: Why Small Increases in Noise Levels may Deserve Serious Consideration,” Transportation Research Record: Journal of the Transportation Research Board, No. 2233, Transportation Research Board of the National Academies, Washington, D.C., 2011, pp. 161–166 This paper “presents historical information on the study of reflections from noise barriers in the U.S., human perception of changes, and also how reflective noise barriers may change the character of noise from highways as heard in communities opposite the barriers.” The authors draw two main conclusions: (1) Small changes in sound level associated with barrier reflections can be meaningful to the public and to their conclusions regarding the effectiveness of noise barriers, and (2) the benefit of simply implementing absorptive barrier treatments opposite residential areas outweighs the benefit of researching the issue or conducting detailed analyses to justify using absorption. The paper provides a brief history of community reaction in the United States to reflections from noise barriers and to the related responses of state DOTs noting that for decades, many DOTs have followed widely accepted guidance that single reflections of noise from noise barriers to the opposite side of highways are “generally one to two dBA or less, and therefore not perceptible to the average human ear.” Despite this guidance, “the outcry from residential communities subject to reflected noise can be quite significant.” Because of such community reaction, some DOTs have spent “significant effort and money spent researching the magnitude of sound level increases both near and far from reflective noise barriers along highways.” As an example of community noise issues that have led to investigations of barrier reflections, the paper describes the “Caltrans Experience.” The authors note that for most, if not all the early decades of highway noise barrier construction, Caltrans led the United States in the total length of noise barriers constructed, and nearly all these were of reflective concrete block. “Perhaps as a result of the sheer number of barriers constructed and the large number of homes affected, Caltrans received its share of complaints from residents about increased noise after barriers were constructed.” Although many of these residents were located at significant distances from the highways and were not exposed to noise levels high enough to constitute noise impact or to warrant noise abatement, Caltrans investigated the complaints to understand their basis and to take appropriate action if any was deemed appropriate. The investigations described in the paper took place in response to community complaints in San Jose, Los Angeles, Alamo, Oakland, and San Rafael (summaries of these studies follow below). The paper also addresses the common guidance that changes in sound level of less than 3 dB are not readily noticeable stating that “researchers have known for decades that under controlled, laboratory situations, listeners can detect changes in broadband noise far smaller than the 3 dB considered a 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 24 Sexton, Timothy, Washington State Department of Transportation. Messages to Douglas Barrett. Nov. 4 and Nov. 25, 2013. E-mail. 25 See, for example: Harris, Cyril M., Handbook of Acoustical Measurements and Noise Control, p. 17.22, 1991.

A-9 less than 0.5 dB.”26 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 like a nearby highway may lead to ingrained expectations regarding typical noise levels and heightened sensitivity to even small changes. • Comparative audio listening tests have demonstrated that frequency shifts as small as 0.1 dB are audible. Residents may discern spectral changes due to reflected sound as a change in sound character and may interpret this change as an increase in level. • Adding reflective surfaces adds new sound propagation paths and may change the temporal characteristics of vehicle pass-bys. For example, residents may notice that truck pass-bys sound different and may interpret this change as an increase in level. Chapter 3 of this appendix details findings from this paper related to the magnitude of noise reflected from barriers and Chapter 4 discusses efforts to reduce reflected noise from barriers. Miller, George A., “Sensitivity to Changes in Intensity of White Noise and Its Relation to Masking and Loudness,” The Journal of the Acoustical Society of America, Volume 19, Number 4, July, 1947 This paper, referenced in the previous document, shows 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. The study, conducted by Harvard University’s Psycho-Acoustic Laboratory, examined sensitivity to changes in the intensity of a random noise over a wide range of intensities. The study found that the “just detectable increment” in the intensity of random noise was of the same order of magnitude as for pure tones. For intensities more than 30 dB above the threshold of hearing for random noise, the size of the increment that can be heard 50% of the time was determined to be approximately constant (0.41 dB). Hatano, M. M., Evaluation of Noise Barrier Reflection 04-SC1-101-30.7, Office of Transportation Laboratory, California Department of Transportation Report No. 1970- 657287, January 1978 This report describes the earliest instance identified by this literature review of an investigation in response to community concerns of sound reflected from a highway noise barrier. In 1978, Caltrans investigated complaints about increased noise from residents near US 101 in San Jose. The complaints concerned a noise barrier constructed by a developer on state right-of-way (ROW) to shield a new residential development. Residents claimed that “they noticed a significant increase in noise level due to noise reflections” from a wall constructed in 1975 on the opposite side of the freeway. The residences involved in the study were located several hundred feet from the edge of pavement and, in 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 dB 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 Chapter A-3. 26 Miller, George A., “Sensitivity to Changes in Intensity of White Noise and Its Relation to Masking and Loudness,” The Journal of the Acoustical Society of America, Volume 19, Number 4, July 1947, p. 609.

A-10 Hendriks, R. and J. Hecker, Parallel Noise Barrier Report: A Noise Absorptive Demonstration Project, San Diego Freeway (I-405), Los Angeles, CA, Caltrans District 7, Environmental Investigations Section, July 1989 Following the construction of parallel, reflective noise barriers along Interstate 405 in the Brentwood section of Los Angeles, Caltrans began to receive complaints about increased noise levels at large distances from the highway. After receiving threats of legal action and a petition by Brentwood residents to remove the noise barriers, which were causing an “intolerable increase in noise levels due to reflection in the neighborhoods,” the Caltrans District 7 Environmental Investigations Section conducted a study of absorptive noise barrier treatments. Results of this study are described in Chapter A-3. Hankard Engineering, North End Neighborhood Noise Study (Colorado Springs), 2000 As part of a highway widening project, the Colorado Department of Transportation (CDOT) constructed a noise barrier along the west side of Interstate I-25 in Colorado Springs in 1998. The wall was designed to reduce traffic noise levels at residences adjacent to the west side of the highway. Shortly after completion of the noise barrier, CDOT began to receive complaints about traffic noise from residents of a neighborhood east of the highway set back several hundred feet to a few thousand feet and generally at a higher elevation than I-25. Residents complained that “I-25 noise is very bothersome, and noticeably higher since construction of the wall.” In 1999, in response to these complaints, CDOT commissioned a noise study for the affected neighborhoods. Results of this study are described in Chapter A-3. Roseen, M., Effects of noise wall located on the east side of TH 100 on noise levels of residences on the west side of TH 100 in the vicinity of Vernon Avenue, Minnesota Department of Transportation, Environmental Analysis and Compliance Section, Environmental Modeling and Testing Unit, January 22, 2002 Following construction of a noise barrier on the east side of TH 100, a six-lane divided highway in Minneapolis, residents on the west side of the road raised concerns about possible increases in traffic noise levels. Due to this reaction, the Minnesota Department of Transportation (MnDOT) conducted a test to determine if construction of the noise barrier had increased noise levels, and if so, the magnitude of the increases. Results of this study are described further in Chapter A-3. Roseen, M., Effects of a noise barrier, located on the west side of TH 47 (University Ave.), on the noise levels of residences on the east side of TH 47 located between 45th Ave. N. and 52nd Ave. N., Minnesota DOT, Environmental Analysis and Compliance Section, Environmental Modeling and Testing Unit, September 20, 2002 In a similar situation to the MnDOT TH 100 project, residents on the east side of University Ave., a four- lane divided arterial in Minneapolis, were concerned about possible increases in traffic noise levels due to construction of a noise 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. Results of this study are described in Chapter A-3.

A-11 Burge, P., J. Crawford, and Peter Wasko, “Use of advanced tools and techniques to resolve an atypical parallel noise barrier case,” Proceedings of Noise-Con 2013, Denver, CO, August 26-28, 2013 As part of a lane addition project along Interstate 94 (I-94), the primary highway link between Minneapolis and St. Paul, Minnesota, an acoustically reflective noise barrier was constructed on the eastbound (southern) side of I-94. The noise impact analysis for the neighborhood north of the highway did not consider possible acoustical reflections, in part because a noise barrier constructed many years earlier on the north side of the highway already was in place. The two walls together formed a parallel barrier condition with the northern neighborhood and barrier at a higher elevation than the southern barrier and community. After the southern wall was constructed, residents north of I-94 complained of increased noise levels. MnDOT commissioned a follow-up study to determine 1) if reflections from the new noise wall were causing perceptively higher noise levels in the adjacent community, and 2) if so, what could be done within project budget constraints to help mitigate the noise level increases. The results of this study are described in Chapter A-4. The following three news articles describe the recent reaction of a community to perceived increases in noise levels due to reflected sound and the response from Caltrans. Swegles, F., “San Clemente to lodge complaints about I-5 wall,” Orange County Register, December 21, 2011, updated August 21, 2013 The San Clemente, California City Council voted 4-0 to send two letters to Caltrans on behalf of two groups of residents. One group living east of Interstate-5 (I-5) in San Clemente wants Caltrans to dismantle a 16-ft-tall freeway sound wall they say is blocking their ocean views and reflecting freeway noise at their homes. Other “residents west of I-5 say they wish Caltrans had extended the wall farther south to protect their homes from freeway noise. [. . .] In one letter, the council will ask [Caltrans] to reopen environmental analysis of the [noise barrier] that Caltrans built without consulting most residents on the east side of the freeway. City Attorney Jeff Oderman concluded that Caltrans [failed to] comply with CEQA. The council will ask for an environmental meeting in San Clemente, inviting all affected residents, followed by studies of view and noise effects on both sides of I-5. In a second letter, the city will ask Caltrans why the I-5 wall ends at West Avenida Cornelio when residents of West Avenida Junipero less than a quarter-mile south say they were promised that the wall would provide a sound barrier for their homes. People living on both sides of I-5 complained about unbearable noise.” Shyong, F., “Caltrans offers to consider changes to I-5 sound wall,” Orange County Register, February 3, 2012, updated August 21, 2013 “[Caltrans officials] affirmed the legality of an I-5 sound wall in San Clemente that has triggered complaints from residents and businesses but offered to work with city and county officials to study the project further and consider changes. In a letter to Mayor Jim Evert . . . , Caltrans District 12 Director Cindy Quon wrote, ‘The department would like to work with city staff to further define the scope of the study area and establish the project limits.’ The re-examination would look at the project’s impact area and could include new noise readings. [. . .] Some residents and businesses on the east side of I-5 have appealed repeatedly to the City Council for relief since the wall was erected on the west side of the freeway above Avenida del Presidente. Those on the east side say the 16 ft. tall wall blocks ocean views and [reflects] freeway noise in their direction. [. . .] The city contends the agency failed to comply with the California Environmental Quality Act by not adequately notifying residents on both sides of the freeway when it solicited neighborhood input about putting up the new walls in a $5.3 million project. Caltrans has said the project qualified for a ‘categorical exemption’ from the Environmental Quality Act because Caltrans

A-12 concluded the sound walls would not have significant effects. Public-outreach efforts by the Orange County Transportation Authority went beyond state and federal requirements, Caltrans said.” Swegles, F., “A quest for peace and quiet,” Orange County Register, September 25, 2013 Although Caltrans agreed to use a sound-absorbing concrete block product on noise barriers to be built as part of a $275 million freeway widening that will begin in 2014 in north San Clemente, residents in south San Clemente still are complaining of noise reflected from a 16-ft noise barrier constructed in 2011. According to a south San Clemente resident, “I saw them working on [the noise barrier],” he said. “As the wall got higher, my noise level went higher. It was just like someone turned up a radio.” Residents on the opposite side of I-5 from the noise barrier claim that they were not able to provide comments “because Caltrans never notified them of stakeholder meetings. The meetings targeted residents closest to the then-proposed wall.” After construction of the noise barrier, people inland (east) of I-5 claimed they were exposed to reflected noise. “They enlisted the city’s help, and the city asked Caltrans to reopen the environmental-review process for the wall, but Caltrans insisted it had followed the state’s environmental rules.” “Now that Caltrans will use the sound-absorbing blocks on the new noise barriers in north San Clemente, [south San Clemente residents] hope to see it applied to the wall below their homes, too. [. . .] ‘We don’t doubt the product,’ [the city’s transportation engineering manager] said. ‘Funding is the challenge.’ [. . .] Dave Richardson, Caltrans spokesman, said he could not comment on whether Caltrans might apply the absorptive product to the 2011 wall as the agency is facing a lawsuit over that project.” Correspondence with Three DOTs The following paragraphs summarize correspondence with representatives from three different state DOTs regarding any incidents of complaints due to reflected noise and the DOT’s response. Correspondence with Jonathan Evans, New Hampshire Department of Transportation, November 1, 2013 To date, NHDOT has not had any experience or issues regarding noise barrier reflection and has not conducted any studies regarding reflected noise. Although they “have had a few complaints here and there, [NHDOT was] able to dismiss those mostly by taking measurements and finding that the noise levels were still below the [Noise Abatement Criteria] NAC or that the neighborhood lacked a Type I project.” For parallel noise barriers, NHDOT has “used the FHWA’s parallel barrier width-to-height ratio of 10:1 as a way to indicate an area that could be affected by reflected noise. The Department’s ROWs are almost always wide enough that no receptors are located within the area of this 10:1 width- to-height ratio.”27 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 27 FHWA guidance states: “Studies have suggested that to avoid a reduction in the performance of parallel reflective noise barriers, the width to height ratio of the roadway section to the barriers should be at least 10:1. The width is the distance between the barriers, and the height is the average height of the barriers above the roadway.” Federal Highway Administration, Highway Traffic Noise: Analysis and Abatement Guidance, p. 60.

A-13 were unfounded.” Noise reflection has not been a significant issue in Florida and they have not done any research/studies in that area. Correspondence with Timothy Sexton, Washington State Department of Transportation, November 4 and 25, 2013 WSDOT has “received complaints on this topic, but staff time limitations restrict their ability to respond in person to all complaints.” Since these situations have fallen outside of their policy guidelines, WSDOT has decided not to collect measurements or pursue a detailed explanation. This approach is reinforced by their lack of a funding mechanism to provide additional mitigation.

A-14 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 101 in San Jose, Caltrans performed one of the first investigations of sound reflected from a highway noise barrier. Although field measurements failed to identify statistically reliable differences between sound levels with and without reflections, Caltrans determined through modeling that theoretical increases in the A-weighted sound level of up to 2 dB were possible. The researchers concluded that this potential increase was not significant, and noted that “changes of 2 to 3 dBA from one day to the next cannot be normally perceived by most people.”28 Approximately 10 years later, Caltrans conducted another study of noise barrier reflections, this time in the Brentwood section of Los Angeles along Interstate 405. Construction of parallel, reflecting noise barriers had generated complaints of an “intolerable increase in noise levels due to reflection in the neighborhoods” at distances 1,000 ft. or more from the highway. The study incorporated controlled noise and meteorological measurements with simultaneous traffic counts, including some with highly absorptive treatment added to the far-side barrier. Caltrans also conducted acoustical modeling and compared it with the measurement results. The measurements showed that near the highway, noise levels decreased by an average of about 1 dB under all wind conditions due to adding absorptive material, with the range of measured decreases from 0 to 3 dB. No decreases in noise levels could be reliably determined at the farther distances. The study concluded that because the noise level decreases were less than 3 dB, which “cannot be discerned by the normal human ear,” the treatment was inaudible and therefore not effective.29 In 1998, Caltrans issued a Technical Advisory providing detailed guidelines for conducting noise and meteorology measurements in response to complaints about reflected sound from barriers. The primary objective of the studies covered by the document was “to determine through measurements if noise barriers inadvertently increase noise levels at distant receivers” generally located 0.15 km to 3 km (about 500 ft. to 10,000 ft.) from highways. Along with guidance on methodology, the document also provided direction for interpreting the significance of measurement results, stating that “a change of 3 dBA or less will be considered no change.” The author noted that he had “conferred with many experts across the nation about performing studies involving distant receivers” with the “general consensus . . . that it is not practical to do Hatano, M. M., Evaluation of Noise Barrier Reflection 04-SC1-101-30.7, Office of Transportation Laboratory, California Department of Transportation Report No. 1970-657287, January 1978. 29 28 Hendriks, R. and J. Hecker, Parallel Noise Barrier Report: A Noise Absorptive Demonstration Project, San Diego Freeway (I-405), Los Angeles, CA, Caltrans District 7, Environmental Investigations Section, July 1989.

A-15 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. Measured 1 to 2 dB increases of average highway traffic noise levels were found to be consistent with predictions and were “suspected to be caused by the presence of a single reflecting sound wall.” The increases, however, were considered insignificant, in accordance with the Caltrans guidelines.31 During this period, other state highway agencies were conducting similar investigations of noise barrier reflections. In 1999, CDOT commissioned a study in response to complaints of reflected sound in a neighborhood set back several hundred feet to a few thousand feet from I-25 in Colorado Springs. Measured A-weighted sound levels were found to have increased by approximately 1 dB following construction of a reflective noise barrier on one side of the highway. Noting that 3 dB “is considered the minimum perceptible change in noise levels in outdoor environments,” the report concluded that application of absorbent material to the east face of the noise barrier “would not provide any perceivable noise reduction” in the affected neighborhood.32 Shortly thereafter, in 2001 and 2002, MnDOT conducted measurement studies at two locations in Minneapolis due to community concerns of possible increases in traffic noise levels caused by construction of single, reflective noise barriers. In each case, noise measurements were repeated at four sites where measurements had been taken prior to construction of the barrier. After normalizing to account for differences in traffic and conducting a statistical analysis of measured sound level differences, MnDOT 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 four measurement sites in each of the two study areas. In each study area, however, the analysis indicated a statistically significant increase of 1 dBA or less at one of four measurement sites. The report concluded that this was not “a detectable change as judged by human hearing” based on FHWA guidance that “the ability of the human ear to detect noise level change is limited to noise level changes of 3 dBA or more.”33 Despite the findings of these investigations that increases in noise due to reflected sound were so small that they should have been imperceptible, in each case people did respond to reflected sound, or at least to the perception of it. Although each study was conducted carefully using what was appropriate methodology, they all focused on the change in the overall A-weighted sound level in the community opposite the barrier. The difficulty is that the changes affected residents perceived may have been related to more than a simple increase in the overall sound level. Assuming unobstructed propagation paths for both the direct and reflected sound, the increase in the total sound level due to adding reflections should be less than the 3 dBA attributable to the doubling of the source energy. As noted above, widespread guidance has held that an increase of less than 3 dBA should not be perceptible under these conditions.34 As discussed above in Chapter A-2, one hypothesis is that the noticeability and annoyance caused by the reflections might be due to other factors such as long-term familiarity with the highway noise source followed by an abrupt change, spectral changes in sound due to reflections, or alteration of the temporal character of vehicle pass-bys.35 30 Hendriks, R., General Guidelines for Studying the Effects of Noise Barriers on Distant Receivers, Technical Advisory TAN-89-01-R9701, California Department of Transportation, November 30, 1998. 31 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. 32 Hankard Engineering, North End Neighborhood Noise Study (Colorado Springs), 2000. 33 U.S. Department of Transportation, Federal Highway Administration, Fundamentals and Abatement of Highway Traffic Noise (Textbook and Training Course); Document 2, Sec. 3.5.1 (Sept. 1980). 34 Federal Highway Administration, Highway Traffic Noise: Analysis and Abatement Guidance, p. 60. 35 Menge and Barrett, op. cit., p. 164.

A-16 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. Other recent studies have begun to look at additional factors, including spectral information, that may be perceived by community members. A study conducted on US 101 in Marin County, California, between 2007 and 2010 to determine the benefits of both absorptive barriers and quieter pavement during a widening project that also included the relocation of an existing noise barrier. Methodologies incorporated in the study included one-third octave band measurements at a reference location above the noise barrier and behind the noise barrier, On-Board Sound Intensity (OBSI) measurements (also one-third octave band), and sophisticated modeling using software capable of three-dimensional ray tracing.36 (See Chapter A-4 for further discussion of the results of this study.) Also, researchers in Texas recently proposed a new method for in-situ measurement of reflections from a highway noise barrier or retaining wall following its construction. The researchers preferred the results obtainable from an in-situ impulse test, but opted to use a broadband, steady-state excitation signal with the same statistical properties as an ideal impulse, rather than a true impulse source. Synchronous averaging of numerous impulse responses caused moving traffic to “vanish” in the long-term and allowed processing of spectral data. As of this writing, only initial testing had been completed on a large reflective retaining wall along IH-30 in Dallas with plans to test the retaining wall again after application of absorptive material.37 In January 2012, the Ohio Department of Transportation (ODOT) issued a Request for Proposals (RFP) that included research into using absorptive noise barriers in single-barrier cases stating that “it is unknown if a discernable difference between sound-absorptive concrete walls vs. reflective concrete walls exists. Research is needed to determine if there is a discernable acoustic benefit that justifies the added expenditure.” The RFP indicated that the project’s research plan should include noise measurements comparing sound-absorptive and reflective concrete walls “to determine if there is a discernable difference at the receptor and noise-sensitive areas opposite the freeway.”38 At a minimum, this leaves open the possibility of investigating other factors in addition to changes in the overall sound level. As of this writing, the results of the research are not yet available.39 36 Donavan, Paul R. and Dana M. Lodico, The Influence of Quieter Pavement & Absorptive Barriers on US 101 in Marin County, Presentation at Transportation Research Board Committee ADC40 Summer Meeting, Asheville, NC, July 2012. 37 Nelson, David A., Terry Dossey, and Manuel Trevino, “A novel method for measuring highway barrier or retaining wall sound reflections in situ,” Proceedings of Noise-Con 2011, Portland, Oregon, July 2011. 38 Comparison and Testing of Various Noise Wall Materials, Request for Proposals issued by Ohio Department of Transportation, ODOT RFP 2013-16. Posted January 25, 2012. 39 Alcala, Noel, Ohio Department of Transportation. Message to Douglas Barrett. Nov. 19, 2013. E-mail.

A-17 Summaries of Cited Works (Past attempts to quantify the magnitude and effects of noise reflected from barriers) Menge, C.W. and D.E. Barrett. “Reflections from Highway Noise Barriers and the Use of Absorptive Materials in the United States: Why Small Increases in Noise Levels may Deserve Serious Consideration” This paper provides a brief history of community reaction in the United States to reflections from noise barriers and the related responses of state DOTs. The part of the paper discussing community reaction is discussed above in Chapter A-2. Because of community reaction to the perception of noise reflected from barriers, some DOTs have spent “significant effort and money…researching the magnitude of sound level increases both near and far from reflective noise barriers along highways.” Perhaps foremost among these has been Caltrans. From the late 1970s on, Caltrans conducted several studies of the effects of reflected sound and the potential benefits of sound-absorptive barriers. In describing the “Caltrans Experience,” this paper provides brief summaries of several of the Caltrans studies. These investigations are summarized below from the original study documents or from related papers or presentations. Further discussion on this paper is found in Chapter A-4. Caltrans Experience Papers The four following documents were summarized in the “Caltrans Experience” section of the paper and describe various investigations conducted by Caltrans over a period of approximately 35 years. Hatano, M. M., Evaluation of Noise Barrier Reflection 04-SC1-101-30.7 As introduced in Chapter A-2, in 1978, Caltrans investigated complaints about increased noise from residents on the opposite side of US 101 in San Jose from a noise barrier constructed by a developer on state ROW to shield a new residential development. The residences involved in the study were located approximately 400 ft. to 650 ft. from the edge of pavement and, in some cases, considerably above the road (approximately 100 ft.). The investigators conducted noise measurements in comparable sections of the highway with the noise barrier and without the noise barrier using a Caltrans diesel maintenance truck to provide a relatively uniform controlled noise source. Also, measurements were conducted with the noise barriers draped with rugs hung over them to add some sound-absorbing qualities. The researchers could not measure statistically reliable sound level differences between the cases without the barrier, with the (reflective) barrier, or with the barrier draped with rugs. Based on the measurements, the researchers concluded that “reflected noise from the walls is not significant” and that “field measurements did not show any consistent measurable differences between the covered and bare walls or at the comparable locations with and without walls.” The researchers also conducted modeling exercises, finding that theoretical increases in the A-weighted noise levels of up to 2 dB were possible, given the geometry. They noted, however, that their “measuring instruments were not sufficiently accurate to clearly define the small differences that may have occurred” making it “impossible to verify theory.” In addition, the report stated that “changes of 2 to 3 dBA from one day to the next cannot be normally perceived by most people.” Hendriks, R. and J. Hecker, Parallel Noise Barrier Report: A Noise Absorptive Demonstration Project, San Diego Freeway (I-405), Los Angeles, CA This Caltrans study along Interstate 405 in the Brentwood section of Los Angeles (introduced in Chapter A-2) included controlled noise and meteorological measurements with simultaneous traffic

A-18 counts. Noise levels were measured near the highway as well as in neighborhoods more than 1,000 ft. from the highway, where many complaints had originated. After adding sound-absorptive treatment to the noise barrier opposite the affected community, Caltrans conducted follow-up measurements. In addition, acoustical modeling was conducted and compared with the measurement results. The measurements indicated that near the highway, adding sound-absorptive material decreased noise levels by an average of about 1 dB under all wind conditions, with measured decreases ranging from 0 to 3 dB. No decreases in noise levels could be reliably determined at the farther distances. The study concluded that because the traffic noise level decreases were less than 3 dB, which “cannot be discerned by the normal human ear,” the treatment was inaudible and therefore not effective. In addition, the researchers found that wind direction had a greater effect on measured A-weighted levels behind the barrier than any reflection effects. Although this demonstration project involved parallel noise barriers, rather than a single, reflective noise barrier, some aspects are relevant to investigations of reflected sound from single barriers. The Caltrans report notes that “daytime noise levels at the far receivers were influenced as much or more by local noise sources, such as lawn mowers pool pumps, construction, and [local street traffic].” Clearly, any measurements to quantify the effects of reflected sound are hindered if the subject highway traffic noise is not the dominant noise source at the measurement locations. In addition, the report notes that “wind speed and direction appear to have a much greater influence on the noise levels at the far receivers than freeway traffic volumes.” This finding underscores the requirement for comparable atmospheric conditions to ensure the validity of comparisons between different sets of noise measurements. Hendriks, R., General Guidelines for Studying the Effects of Noise Barriers on Distant Receivers, Technical Advisory TAN-89-01-R9701, California Department of Transportation, November 30, 1998 This Technical Advisory provided detailed guidelines for conducting noise and meteorology measurements in response to complaints about reflected noise from barriers. The primary objective of the before-and-after noise barrier studies covered by the document was to determine through measurements if noise barriers inadvertently increase noise levels at distant receivers. The guidelines and criteria were written to cover complex, non-routine noise barrier noise studies for receivers generally located 0.15 to 3 km (approximately 500 to 10,000 ft.) from highways. At the time of this Technical Advisory, such studies had been performed on a limited basis in the San Francisco Bay Area because of public concern that noise barriers increased noise levels at distances beyond 400 m (approximately 1,300 ft.) from freeways. Along with providing guidance on methodology, the document also presented direction for interpreting the significance of measurement results, stating that “a change of 3 dBA or less will be considered no change.” The author noted that “many of the guidelines given should be considered experimental,” and also that “additional guidelines may be necessary to cover specific site conditions, and some of the guidelines may have to be changed if experience and future studies show a need for it.” In addition, the author stated that he has “conferred with many experts across the nation about performing studies involving distant receivers. The consensus is that it is not practical to do these studies on a routine basis because of their high cost, both in terms of money and necessary resources.” 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

A-19 differences in noise levels “before” and “after” the installation of the noise barriers at locations relatively distant from the freeway traffic noise source. The measurement program followed guidelines developed by Caltrans (Technical Advisory TAN-9701-R9301, a predecessor to TAN-98-01-R9701), including simultaneous noise, meteorological and traffic data collection before and after the construction of noise barriers. Measured traffic noise levels were normalized for traffic conditions and carefully categorized by meteorological condition. Two receivers were located opposite the barrier at distances of 330 ft. (100 m) and 950 ft. (290 m) on a hillside elevated above the roadway. The only data reported for these receivers was collected at night with relatively calm winds and clear skies. Before-and-after noise levels grouped in similar meteorological categories were compared to evaluate noise level changes. Average highway traffic noise levels (Leq) were observed to increase by approximately 1 dB at the closer receiver and 2 dB at the more distant receiver. Although the report noted that the measured increases were consistent with sound prediction theory that predicts an increase of 0 to 3 dB “and suspected to be caused by the presence of a single reflecting sound wall,” the increases were considered insignificant, in accordance with Caltrans guidelines. Hankard Engineering, North End Neighborhood Noise Study As discussed earlier in Chapter A-2, CDOT conducted this study to determine the effects of a noise barrier constructed along the west side of Interstate I-25 in Colorado Springs on residents of a neighborhood east of the highway. The neighbored was back several hundred feet to a few thousand feet and generally at a higher elevation than I-25. The study included collection of noise levels, traffic volumes, and meteorological data at six locations from July 1 through September 24, 1999. Analysis of the measurement data indicated that I-25 was the predominant noise source throughout much of the study area, particularly on the west side, closest to I-25. At other locations in the study area, farther from I-25 and closer to busier local streets, noise from local traffic influenced noise levels. At one site, located approximately 1,000 ft. from I-25 with an unobstructed line of sight to the roadway, noise levels were measured from January to March 1998, prior to construction of the wall, and again during September and October 1998, following the wall’s completion. Noise levels at this location were found to increase by approximately 1 dB following construction of the wall. Noting that 3 dB “is considered the minimum perceptible change in noise levels in outdoor environments,” the report concluded that application of absorbent material to the east face of the noise barrier “would not provide any perceivable noise reduction” in the affected neighborhood. MnDOT Studies The two following documents describe two similar studies conducted by MnDOT in response to community concerns about noise barrier reflections. Roseen, M., Effects of noise wall located on the east side of TH 100 on noise levels of residences on the west side of TH 100 in the vicinity of Vernon Avenue. Residents on the west side of TH 100, a six-lane divided highway in Minneapolis, expressed concern about possible increases in traffic noise levels due to construction of a noise barrier on the east 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 (see also Chapter A-2). In 2001, following construction of the barrier, MnDOT repeated noise measurements at four sites opposite the barrier where measurements had been conducted in 2000, prior to construction of the barrier. Traffic classification counts were conducted during both sets of measurements, and the measured 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

A-20 three of the four measurement sites. At the fourth site, however, the analysis indicated a statistically significant increase of approximately 0.5 dBA due to construction of the noise barrier. The report concluded that this increase was not “a detectable change as judged by human hearing” based on FHWA guidance that “the ability of the human ear to detect noise level change is limited to noise level changes of 3 dBA or more.”40 Roseen, M., Effects of a noise barrier, located on the west side of TH 47 (University Ave.), on the noise levels of residences on the east side of TH 47 located between 45th Ave. N. and 52nd Ave. N. As introduced in Chapter A-2, residents on the east side of University Avenue, a four-lane divided arterial highway in Minneapolis, were concerned about possible increases in traffic noise levels due to construction of a noise 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. In 2002, following construction of the barrier, noise measurements were repeated at four east-side residences where measurements had been conducted in 2000, prior to construction of the barrier. Traffic classification counts were conducted during both sets of measurements, and the measured 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. At the fourth site, however, the analysis indicated a statistically significant increase of approximately 1 dBA due to construction of the noise barrier. The report concluded that this increase was not “a detectable change as judged by human hearing” based on FHWA guidance that “the ability of the human ear to detect noise level change is limited to noise level changes of 3 dBA or more.”41 Comparison and Testing of Various Noise Wall Materials, Request for Proposals issued by Ohio Department of Transportation, ODOT RFP 2013-16. Posted January 25, 2012 This RFP from ODOT provides another example of a state DOT funding research to better understand the magnitude and effects of sound reflected from noise barriers. The RFP included three research topics concerning highway noise barriers; the second topic addressed using absorptive barriers in single-barrier cases. The problem statement was as follows: ODOT’s current noise policy is to use sound-absorptive material if there are noise-sensitive areas opposite the freeway. This results in additional costs to ODOT for the inclusion of the sound-absorptive materials. It is unknown if a discernable difference between sound- absorptive concrete walls vs. reflective concrete walls exists. Research is needed to determine if there is a discernable acoustic benefit that justifies the added expenditure. Durability of this material is a potential issue as well. Research relative to the durability of this material over time is needed on existing noise walls. 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. Statistically validate the findings. Research the durability of 40 U.S. Department of Transportation, Federal Highway Administration, Fundamentals and Abatement of Highway Traffic Noise (Textbook and Training Course); Document 2, Sec. 3.5.1, Sept. 1980. 41 Ibid.

A-21 this material on existing noise walls. Provide recommendations on the most appropriate use of sound-absorptive materials that will ensure ODOT a return on investment from the initial higher construction costs of these types of walls. The results of this research will be used by decision makers to determine if, and when, to use sound- absorptive materials on concrete noise walls. As of this writing, the results of the research are not yet available.42 Nelson, David A., Terry Dossey, and Manuel Trevino, “A novel method for measuring highway barrier or retaining wall sound reflections in situ,” Proceedings of Noise-Con 2011, Portland, Oregon, July 2011 This paper proposes a new method for measuring reflections from a highway noise barrier or retaining wall following its construction. In a recent project it became necessary to determine the sound-reflective properties of such a wall before and after the installation of sound-absorbing material to assess the performance of the absorbing material. Conventional methods, such as impedance tube testing and impulse testing, were deemed undesirable because of small area coverage and the potential for startling drivers. Attempts to measure absorptive properties by observing sound level differences due to live traffic passing in front of reflective and absorptive sections must consider changes in traffic volume, speed, vehicle mix, or lane selection. Laboratory tests also have limitations because they are not able to fully address reflection properties of an extended surface or the potential differences in performance of field-installed treatments. The authors preferred the results obtainable from an in-situ impulse test, but desired that the “impulse” be generated in some other manner other than a true impulse. Maximum-length sequence (MLS or m- sequence) analysis, which uses a broadband, steady-state excitation signal with the same statistical properties as an ideal impulse, was employed to determine the impulse response of reflections off the wall. Synchronous averaging of numerous impulse responses causes moving traffic to “vanish” in the long term. Results have been shown to be comparable to impedance tube tests. Although the method is “conceptually robust and straightforward,” it can be affected by various factors requiring careful consideration. Initial tests were performed on a large retaining wall along IH-30 in Dallas, Texas, to fine-tune the method into its current form. The initial testing showed that it is possible to directly measure reflections from extended surfaces, using the MLS method to obtain impulse responses without resorting to impulsive sources. As of this writing, only initial testing had been completed on the reflective retaining wall, with plans to test the retaining wall again after its treatment to assess the reduction in noise level. McNerney, Michael, S.M. Bucsak, E.J. Haden, and K. Liapa, Relational Database of Texas Noise Barriers and Effectiveness of Absorptive Treatments Applied to Noise Barriers, Center for Transportation Research, The University of Texas at Austin, Project 0-2112 Summary Report, August 2001 As part of a project to develop a GIS-based relational database of Texas noise barriers, the authors also conducted research to construct a database of acoustically absorptive treatments on noise barriers. Four different manufacturers participated with noise barriers along IH 610 in Houston. Three of the noise barriers included absorptive materials; the fourth was reflective. To evaluate the effectiveness of the sound- absorptive materials, the researchers placed a microphone within 15 cm (approximately 6 inches) of the front of the wall. The sound source for the test was the existing traffic flow from the highway. Using an artificial sound source was ruled out during preliminary tests, and a controlled natural sound source was not feasible because of heavy traffic along IH 610. The results were normalized for differences in source 42 Alcala, Noel, Ohio Department of Transportation. Message to Douglas Barrett. Nov. 19, 2013. E-mail.

A-22 strength using a reference microphone. The reflective noise barrier was used as the control, and the measured difference in sound pressure level between it and each of the three absorptive barriers was attributed to the absorptive surfaces. Compared to the reflective noise barrier, sound levels measured near the absorptive barriers ranged from about 1.5 dB to about 4 dB lower. Note that these measurements were conducted within the roadway ROW immediately in front of the reflective barrier, as opposed to at a community location outside of the ROW across the highway from the reflective barrier.

A-23 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 United States, in part due to the different approaches pursued by various state highway agencies. As described in Chapters A-2 and A-3, some DOTs have responded to community concerns about sound reflected from noise barriers by conducting investigations to attempt documenting perceived increases in noise. Other DOTs have chosen to address similar community concerns by adding sound-absorptive materials to barriers after construction, while still others have long-standing practices of using barriers with absorptive surfaces where there is noise-sensitive land use on the opposite side of the highway. During the 1980s and 1990s, DOTs in several states, including Massachusetts, New York, New Jersey, Maryland, and Virginia, started to specify sound- absorbing barriers opposite residential areas when confronted with complaints from residents regarding reflected sound. As noted in Menge and Barrett (2011), “Although these states did not institute formal policies, they adopted informal, but widespread practices, of specifying sound-absorptive barriers in locations where reflected sound was of concern – where there was residential land use or another barrier on the opposite side of the roadway.” 43 Since 2010, FHWA has required state highway agencies to include provisions in their state noise policies for use of absorptive treatment on roadside structures, including noise barriers, retaining walls, bridges, and any other structure the highway agency may consider for application of a sound-absorptive material.44 In response to this requirement, some states have adopted formal policies either requiring use or consideration of absorptive treatment on noise barriers in some situations: • Since 1988, the Wisconsin Department of Transportation (WisDOT) Transportation Facilities Development Manual has required that if noise abatement is found to be reasonable and feasible and is proposed for installation, absorptive noise barrier surfaces are required for use “on the roadway side of a single-side-of-roadway noise wall, when residential or other noise-sensitive receptors are located opposite from the roadway wall face.”45 • ODOT permits installation of sound-absorptive noise barriers when approved by its Office of Environmental Services. Typical uses for sound-absorptive noise barriers have been where there are noise-sensitive areas across from a proposed noise wall or where parallel barriers are proposed. However, in “isolated areas with no noise-sensitive land use on the opposite side of the roadway” reflective barriers are required.46 43 Menge and Barrett, op. cit. 44 Federal Highway Administration, Highway Traffic Noise: Analysis and Abatement Guidance, p. 60. 45 Wisconsin Department of Transportation Facilities Development Manual, Chapter 23 “Noise,” Section 35 “Noise Abatement Measures,” February 15, 1988. 46 Ohio Department of Transportation Highway Traffic Noise Analysis Manual, Analysis and Abatement of Traffic Noise, Ohio Department of Transportation, Office of Environmental Services, February 2013, p. VII-3.

A-24 • In its Environmental Procedures Manual, the Tennessee Department of Transportation (TDOT) acknowledges that “noise reflections off of a noise barrier on one side of a highway can . . . increase sound levels on the opposite side of the highway.” While stating that “in most cases, these increases are less than 3 dB which is usually the smallest change in hourly sound levels that people can detect without specifically listening for the change,” TDOT may consider specifying single noise barriers as absorptive if there are noise-sensitive land uses on the opposite side of the road from the noise barrier.47 • “Depending on the specifics of the transportation improvement project,” the Virginia Department of Transportation (VDOT) may recommend absorptive noise barrier surfaces in the presence of “an extremely sensitive receptor(s) on the side opposite the highway from the proposed noise barrier” or in the “presence of impacted receptors on the side opposite the highway for whom a noise barrier was not determined to be feasible or reasonable.” In these cases, the determination of whether to use absorptive materials is guided by the ratio of the barrier-to-receiver distance compared to the height of the barrier.48 A long-term success story in reducing reflected noise and related community complaints through a policy promoting widespread use of sound-absorptive barriers comes from Ontario, Canada. The Ontario Ministry of Transportation (MTO) has “an aggressive policy in dealing with unwanted reflections from single [and parallel] noise barriers,” and has constructed approximately 104 km (65 miles) of absorptive noise barriers since 1978. Because of this practice, barrier reflections are “just not a problem” in Ontario.49 In addition to the investigations described in Chapter A-3 that measured the magnitude and effects of noise reflected from barriers, other studies have attempted to measure the success of efforts to reduce reflected noise. A 1999 study in Oakland, California, evaluated a progression of noise abatement treatments including noise barriers and sound-absorbing panels along a section of I-580. In this project, noise barriers were constructed on one side of the freeway and on a median retaining wall, but were not feasible for residences on the opposite side due to a large elevation difference between the homes and the road. Following construction of the noise barriers, the insertion loss was found to be only 3 to 4 dB, not sufficient noise reduction for the barrier to be considered effective. The median retaining wall and noise barrier then were covered with sound-absorbing panels and the insertion loss was measured to be 5 dB, sufficient to be considered effective. This is an example of where an “imperceptible” one- to two-decibel change made the difference between an ineffective and effective barrier.50 Another California study, this one conducted during a widening project on US 101 in Marin County between 2007 and 2010, investigated the benefits of both absorptive barriers and quieter pavement. Prior to the project, noise barriers existed on both sides of the highway; however, adding a 16-ft.-wide multiuse path necessitated relocating one barrier farther from the roadway. Because of residents’ concerns about reflected sound, absorption was added to the barriers on both sides. Although attempts to measure the benefit of the absorptive materials were inconclusive due to changes in geometry and varying pavement during different project phases, modeling indicated that the absorptive materials could reduce noise levels by 3 to 5 dB at distant (those over 500 ft. from road) and elevated receptors. The benefit would be less 47 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. 48 Virginia Department of Transportation Highway Traffic Noise Impact Analysis Guidance Manual (Version 4), Section 10.4 “Applications for Absorptive Noise Barriers,” August 6, 2013, pp. 32-33. 49 Blaney, Christopher, Ontario Ministry of Transportation. Message to Douglas Barrett. Nov. 4, 2013. E-mail. 50 Woodward-Clyde and Illingworth & Rodkin, Inc., Noise Abatement Evaluation: Interstate 580 Oakland, Reference 4-ALA-580, HP 311 Program, November 1999.

A-25 (1 to 2.5 dB) at closer receptors.51 This project involved parallel barriers, but some of the findings are relevant to measurement studies of single-barrier reflections. In particular, relevance was found in the influence of whether the receptor had a clear line of sight to either the roadway or the reflective noise barrier and the importance of controlling any variability in conditions between measurements of “no barrier” and “with barrier” cases. Finally, a recent study commissioned by MnDOT investigated potential causes and solutions to community noise complaints following construction of a new noise barrier. As part of a lane addition project along Interstate 94 (I-94) between Minneapolis and St. Paul, a reflective noise barrier was installed across from a noise barrier constructed many years earlier. The study found that the new noise barrier was creating unshielded acoustical reflections to some receivers previously protected by the existing barrier, with the largest increases for those receiver locations with direct lines of sight to the new barrier. The study recommended that the most effective and cost-efficient mitigation option was to add “backless” acoustical panels, which would provide acoustical absorption without the added cost and weight provided by a solid back panel, to the new noise barrier.52 Summaries of Cited Works (The success of efforts to reduce noise reflected from barriers) Menge, C.W. and D.E. Barrett. “Reflections from Highway Noise Barriers and the Use of Absorptive Materials in the United States: Why Small Increases in Noise Levels may Deserve Serious Consideration” (This paper is also discussed in Chapters A-2 and A-3.) Since the 1970s, some DOTs have responded to community concerns by conducting investigations to attempt to document the effects (or not) of noise reflected from barriers. Other DOTs have attempted to address similar community concerns by adding sound-absorptive materials to barriers after construction, while still others have long-standing practices of using barriers with absorptive surfaces wherever there is noise-sensitive land use on the opposite side of the highway. During the 1980s and 1990s, DOTs in several states, including Massachusetts, New York, New Jersey, Maryland, and Virginia, started to specify sound- absorbing barriers opposite residential areas when confronted by complaints from residents regarding reflected sound. “Although these states did not institute formal policies, they adopted informal, but widespread practices, of specifying sound-absorptive barriers in locations where reflected sound was of concern – where there was residential land use or another barrier on the opposite side of the roadway.” The authors note that “public funds spent on sound-absorptive barriers are perceived as benefiting the public whereas funds spent disputing or attempting to disprove residents’ claims may be perceived as opposing the public.” In addition, the authors contend that the benefit of simply implementing absorptive barrier treatments opposite residential areas outweighs the benefit of researching the issue or conducting detailed analyses to justify using absorption, even if that use comes at a modest cost premium. Correspondence with Chris Blaney, Ontario Ministry of Transportation, November 4, 2013 The Ontario 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. Ontario has “had an aggressive 51 Donavan, Paul R. and Dana M. Lodico, The Influence of Quieter Pavement & Absorptive Barriers on US 101 in Marin County, Presentation at Transportation Research Board Committee ADC40 Summer Meeting, Asheville, NC, July 2012. 52 Burge, P., J. Crawford, and Peter Wasko, “Use of advanced tools and techniques to resolve an atypical parallel noise barrier case,” Proceedings of Noise-Con 2013, Denver, CO, August 26-28, 2013.

A-26 policy in dealing with unwanted reflections from single [and parallel] noise barriers,” having always used absorptive noise barriers in those situations. MTO does not build a single sound-reflective noise barrier where there are noise-sensitive areas on the opposite side of the highway. In addition, they generally try “to construct noise barriers on both sides of the highway at the same time to avoid the perception of reflections.” As a result, “this is just not a problem” in Ontario. MTO’s official policy states that sound-absorptive noise barriers are recommended in retrofit barrier sites where parallel sites are being constructed or where there are single sites being constructed where the unwanted reflection may cause problems. It is only a practice (i.e., not policy) for sites constructed for environmental mitigation purposes. MTO is in the process of changing their policy and generally follows the guidance provided in the Caltrans Noise Protocol and the Technical Noise Supplement. MTO started constructing sound-absorptive walls in 1978 because they “were aware of the problem.” Since that date, MTO has constructed approximately 104 km (65 miles) of absorptive walls. All noise barriers must be preapproved for use by MTO and must have a Noise Reduction Coefficient (NRC) greater than or equal to 0.70 to be considered as sound absorptive. Although MTO has had complaints due to perceived reflections despite using absorptive materials, the complaints “generally go away once [MTO] explains that over 70% of the sound is absorbed by the walls.” MTO acknowledges that “there may however be cases where even small reflections may cause changes to the tone of the noise rather than the absolute sound levels.” Ohio, Tennessee, Wisconsin, and Virginia DOT Policy and Guidance Examples The four following selections provide examples of the formal policies or guidance of four state DOTs (Ohio, Tennessee, Wisconsin, and Virginia) addressing sound-absorptive noise barrier materials. Ohio Department of Transportation Highway Traffic Noise Analysis Manual, Analysis and Abatement of Traffic Noise, Ohio Department of Transportation, Office of Environmental Services, February 2013 ODOT permits installation of sound-absorptive noise barriers when approved by its Office of Environmental Services. Typical uses for sound-absorptive noise barriers have been where there are noise-sensitive areas across from a proposed noise wall or where parallel barriers are proposed. The manual notes that, in the case of parallel noise barriers, if the width-to-height ratio of the roadway section to the noise barrier is at least 10:1, using absorptive materials on noise walls is not required based on FHWA guidance and research. For example, this means that using absorptive material for two parallel barriers 10 ft. tall and 120 ft. apart is not required. In “isolated areas with no noise-sensitive land use on the opposite side of the roadway” reflective barriers are required, including in locations where future development may result in a noise-sensitive land use on the opposite side of the roadway. In addition, reflective barriers are required in locations with industrial or commercial use on the opposite side of the roadway. 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 FHWA’s Traffic Noise Model’s “Parallel Barriers” module. If noise reflections are predicted to “substantially degrade” the predicted design-year noise reductions, TDOT will use

A-27 absorptive noise barrier materials. TDOT also acknowledges that “noise reflections off of a noise barrier on one side of a highway can also increase sound levels on the opposite side of the highway.” While stating that “in most cases, these increases are less than 3 dB which is usually the smallest change in hourly sound levels that people can detect without specifically listening for the change,” TDOT may consider specifying single noise barriers as absorptive if there are noise-sensitive land uses on the opposite side of the road from the noise barrier.53 Wisconsin Department of Transportation Facilities Development Manual, Chapter 23 “Noise,” Section 35 “Noise Abatement Measures,” February 15, 1988 WisDOT states in its Transportation Facilities Development Manual that “the principles of acoustics indicate that sound reflected from the surface of a noise wall has the potential of increasing sound levels at existing noise-sensitive receptors located on the opposite side of the roadway from the proposed noise wall project. Specifying an absorptive noise wall will reduce reflected sound levels by eighty percent or more, thereby reducing reflected sound to below the level noticeable to the healthy human ear.” If noise abatement is found to be reasonable and feasible and is proposed for installation, absorptive noise barrier surfaces are required for use on any of the following noise wall installations: • Roadway side of parallel noise walls, when installed initially as a pair, or separately as part of an approved, multiyear noise abatement plan. • Roadway side of a single-side-of-roadway noise wall, when residential or other noise- sensitive receptors are located opposite from the roadway wall face. • Residential side of the noise wall, when residential or other noise-sensitive receptors may be affected by reflected noise from other sources located on the residential side of the noise wall. In addition, if reflected noise has the potential to impact lands that are currently undeveloped, the designer must consider proposed land uses for the undeveloped lands when selecting the noise wall surface type. For purposes of these criteria, WisDOT defines an “absorptive noise wall surface” as a noise wall system having a composite NRC of at least 0.80 on the roadway side of the noise wall and 0.70 on the residential side, as applicable. 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. 32-33 VDOT may recommend absorptive noise barrier surfaces “depending on the specifics of the transportation improvement project . . . to optimize the benefits of the proposed highway traffic noise abatement.” Such cases may include the following: • A parallel noise barrier system. • Presence of extremely sensitive receptor(s) on the side opposite the highway from the proposed noise barrier. 53 TDOT has opted to specify absorptive treatment for single noise barriers on three projects where noise-sensitive land uses existed opposite the noise barrier: I-40 eastbound between I-65 South and I-65 North in Nashville, I-240 northbound between Poplar Avenue and Walnut Grove Road in Memphis, and I-65 southbound south of Wedgewood Avenue in Nashville.

A-28 • Presence of a retaining wall with a reflective surface on the side opposite the highway from the proposed reflective-surfaced noise barrier. • Presence of impacted receptors on the side opposite the highway for whom a noise barrier was not determined to be feasible or reasonable. • A bifurcated highway system. Such cases may also include the following in the case of a single barrier parallel to residential noise- sensitive receptors: • If the distance from the barrier to the receptors is greater than 20 times the barrier height, a reflective barrier shall be used. • If the distance from the barrier to the receptors is between 20 times and 10 times the barrier height, consideration will be given to using absorptive barriers. • If the distance from the barrier to the receptors is less than 10 times the barrier height, an absorptive barrier shall be used. The next two selections describe two more examples in the series of Caltrans investigations into the effects of reflections from noise barriers. They are included in this section because they focus on potential mitigation measures. Noise Abatement Evaluation: Interstate 580 Oakland, Reference 4-ALA-580, HP 311 Program, prepared by Woodward-Clyde and Illingworth & Rodkin, Inc., November 1999 This study evaluated a progression of noise abatement treatments, including noise barriers and sound- absorbing panels along a section of I-580 in Oakland. This part of I-580 has superelevated lanes, where the eastbound lanes are about 1 to 4 m (about 3 to 14 ft.) higher than the westbound lanes. The two directions of travel are separated by a retaining wall. Noise abatement was designed to reduce noise levels at residences along the westbound side; noise reduction was not feasible for residences along the eastbound side due to a large elevation difference with the homes located above the freeway. Detailed noise and meteorology measurements were conducted at several sites behind the barrier (westbound side) and at a site representative of the closest residences opposite the barrier (eastbound side). Noise abatement measures included a noise barrier located at the edge of the westbound lane, a second noise barrier located on top of the median retaining wall, and application of sound-absorbing panels to the median retaining wall and the new median noise barrier. Following construction of the noise barriers, an increase of 2 dB was measured at the receiver opposite the edge-of-pavement barrier (eastbound side). Behind the barrier (westbound side), the insertion loss was found to be only 3 to 4 dB, not sufficient noise reduction for the barrier to be considered effective. The 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. Although the application of sound-absorbing panels to the median walls improved the noise reduction for residences on the westbound side, unprotected residences on the eastbound side were left with the 2 dB increase attributed to sound reflected from the new noise barrier.

A-29 Donavan, Paul R. and Dana M. Lodico, The Influence of Quieter Pavement & Absorptive Barriers on US 101 in Marin County, Presentation at Transportation Research Board Committee ADC40 Summer Meeting, Asheville, NC, July 2012 As noted in Chapter A-3, Donavan and Lodico conducted a study to determine the benefits of various noise abatement measures during a 2007 widening project on US 101 in Marin County, California. Prior to the project, noise barriers existed on both sides of the highway. The project added a high-occupancy vehicle lane in each direction and a 16-ft wide multiuse path on the southbound side. The multiuse path necessitated relocating the barrier in the southbound direction farther from the roadway. In addition, because of residents’ concerns about reflected sound, absorption was added to the barriers on both sides. As a result of the project, overall sound levels dropped by about 6 to7 dB. OBSI measurements indicated that most of the improvement was due to the new pavement. Attempts to measure the benefit of the absorptive noise barrier materials were inconclusive due to changes in geometry and varying pavement during different project phases. The effect of the absorptive treatment was modeled using both a spreadsheet approach and SoundPLAN’s implementation of the 1978 FHWA traffic noise prediction algorithm. The modeling indicated that the absorptive materials could reduce noise levels by 3 to 5 dB at distant (those over 500 ft. [152 m] from road) and elevated receptors. The benefit would be less (1 to 2.5 dB) at closer receptors. This project involved parallel barriers, but some aspects are relevant to the situation with a single reflective barrier. Modeling indicated that the effects of reflections were dependent on both the distance and height of receptors relative to the roadway. In addition, whether the receptor had a clear line of sight to either the roadway or the reflective barrier influenced the modeled results. Finally, the difficulty in obtaining conclusive measurement results emphasizes the importance of eliminating all variability, to the extent possible, between “no barrier” and “with barrier” conditions. Burge, P., J. Crawford, and Peter Wasko, “Use of advanced tools and techniques to resolve an atypical parallel noise barrier case,” Proceedings of Noise-Con 2013, Denver, CO, August 26-28, 2013 As discussed in Chapter A-2, as part of a lane addition project along Interstate 94 (I-94), the primary highway link between Minneapolis and St. Paul, Minnesota, a reflective noise barrier was constructed on the eastbound (southern) side of I-94 opposite a noise barrier constructed many years earlier on the north side of the highway. The two walls together formed a parallel barrier condition with the northern neighborhood and barrier at a higher elevation than the southern barrier and community. MnDOT commissioned a study to answer two questions: (1) if reflections from the new noise wall were causing perceptively higher noise levels in the adjacent community, and (2) if so, what could be done within project budget constraints to help mitigate the noise level increases. The study indicated that in addition to a moderate increase in noise due to the additional traffic lanes, the new southern wall was creating new unshielded acoustical reflections to some receivers previously protected by the existing barrier. Although the influence of the added traffic lanes was consistent among all receivers (approximately 1 dBA due to the approximate 33% increase in traffic capacity), the 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. The study found that the most effective and cost-efficient mitigation option was to add acoustical absorption to the south wall. Several materials and products were investigated including prefabricated acoustical panels, spray-on material, and a “backless” acoustical panel, which included a lightweight perforated front panel, acoustically absorptive material behind, but no solid back panel. The cost/benefit analysis showed that the backless panel design would provide the required acoustical absorption to reduce

A-30 reflected noise to a “less than noticeable” level increase at the most economical cost. The advantage of the backless panel is that it would provide acoustical absorption without the added cost and weight provided by a solid back panel, which was not needed due to the mass of the existing barrier. Although this study involved parallel barriers, rather than a single barrier, some of the findings are relevant to investigations of reflections from single barriers. The study showed that construction of a reflective barrier may provide new, unshielded sound propagation paths that may dominate overall sound levels at some locations. Even in single-barrier situations, terrain, retaining walls, or other structures may block the direct line of sight to traffic, and construction of a noise barrier on the opposite side of the road may cause new unshielded paths. In addition, the recommended mitigation approach of the “backless” acoustical panel may also prove effective in single-barrier cases.

A-31 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 the following: (1) the community noise issues that have led to investigations of noise reflected from barriers, (2) past attempts to quantify the magnitude and effects of noise reflected from barriers, and (3) the success of efforts to reduce noise reflected from barriers. Based on this review, the project team offers the following conclusions: • Community complaints of sound reflected from highway noise barriers nearly date back to the first widespread construction of noise barriers in the United States in the 1970s. For many years, on many occasions, and in many different states, communities have complained of sound reflected from highway noise barriers to receptors on the other side of the highway. • Over the past several decades, there have been numerous attempts to quantify the magnitude and effects of noise reflected from barriers. Generally, these studies have identified 0 to 3 dB increases in overall A-weighted sound level because of reflected sound. • In some cases, depending on geometry, even a single reflection may increase sound levels by more than 3 dB, particularly when construction of a noise barrier creates new, unshielded sound propagation paths. • Despite conclusions that increases in noise levels caused by reflections were so small that they should have been imperceptible, in many cases people did respond to reflected sound, or at least to the perception of it. • It is likely that factors in addition to the increase in overall sound level contribute to residents’ perception of increased noise due to reflected sound. Accordingly, investigations of reflected sound should examine additional factors such as spectral changes or alterations of the temporal characteristics of vehicle pass-bys.

A-32 R E F E R E N C E S Berrios, Mariano, Florida Department of Transportation. Message to Douglas Barrett. November 7, 2013. E-mail. Blaney, Christopher, Ontario Ministry of Transportation. Message to Douglas Barrett. Nov. 4, 2013. E-mail. Burge, P., J. Crawford, and Peter Wasko, “Use of advanced tools and techniques to resolve an atypical parallel noise barrier case.” Proceedings of Noise-Con 2013, Denver, CO. August 26-28, 2013. Donavan, Paul R. and Dana M. Lodico, The Influence of Quieter Pavement and Absorptive Barriers on US 101 in Marin County. Presentation at Transportation Research Board Committee ADC40 Summer Meeting, Asheville, NC. July 2012. Evans, Jonathan, New Hampshire Department of Transportation Message to Douglas Barrett. Nov. 1, 2013. E-mail. Federal Highway Administration, Fundamentals and Abatement of Highway Traffic Noise: Textbook and Training Course. U.S. Department of Transportation, Sept. 1980. Federal Highway Administration, Highway Traffic Noise: Analysis and Abatement Guidance, FHWA- HEP-10-025, December 2011. Federal Highway Administration, Summary of Noise Barriers Constructed by December 31, 2010, FHWA-HEP-12-044, July 2012. Hankard Engineering, North End Neighborhood Noise Study (Colorado Springs). 2000. Hatano, M. M. Evaluation of Noise Barrier Reflection 04-SC1-101-30.7. Rep. No. 1970-657287. California Department of Transportation, January 1978. Hendriks, R., General Guidelines for Studying the Effects of Noise Barriers on Distant Receivers. Technical Advisory TAN-89-01-R9701. California Department of Transportation, November 30, 1998. Hendriks, R. and J. Hecker, Parallel Noise Barrier Report: A Noise Absorptive Demonstration Project, San Diego Freeway (I-405), Los Angeles, CA. Caltrans District 7, Environmental Investigations Section, July 1989. McNerney, Michael, S.M. Bucsak, E.J. Haden, and K. Liapa, Relational Database of Texas Noise Barriers and Effectiveness of Absorptive Treatments Applied to Noise Barrier. Center for Transportation Research, The University of Texas at Austin. Project 0-2112 Report. August 2001. Menge, Christopher W., and Douglas E. Barrett. "Reflections from Highway Noise Barriers and the Use of Absorptive Materials in the United States: Why Small Increases in Noise Levels May Deserve Serious Consideration." Transportation Research Record: Journal of the Transportation Research Board, No. 2233 (2011): 161–66. Miller, George A. "Sensitivity to Changes in Intensity of White Noise and Its Relation to Masking and Loudness." The Journal of the Acoustical Society of America, Vol. 19, No. 4, July 1947. Nelson, David A., Terry Dossey, and Manuel Trevino, “A novel method for measuring highway barrier or retaining wall sound reflections in situ.” Proceedings of Noise-Con 2011. Portland, Oregon, July 2011. Ohio Department of Transportation. Comparison and Testing of Various Noise Wall Materials. Request for Proposals issued by Ohio Department of Transportation, ODOT RFP 2013-16, Posted January 25, 2012. Ohio Department of Transportation. Highway Traffic Noise Analysis Manual, Analysis and Abatement of Traffic Noise. Ohio Department of Transportation, Office of Environmental Services. February 2013.

A-33 Roseen, M., Effects of a noise barrier, located on the west side of TH 47 (University Ave.), on the noise levels of residences on the east side of TH 47 located between 45th Ave. N. and 52nd Ave. N. Minnesota DOT, Environmental Analysis and Compliance Section, Environmental Modeling and Testing Unit. September 20, 2002. Roseen, M., Effects of noise wall located on the east side of TH 100 on noise levels of residences on the west side of TH 100 in the vicinity of Vernon Avenue. Minnesota DOT, Environmental Analysis and Compliance Section, Environmental Modeling and Testing Unit. January 22, 2002. Sexton, Timothy, Washington State Department of Transportation. Messages to Douglas Barrett. Nov. 4 and Nov. 25, 2013. E-mail. Shyong, F., “Caltrans offers to consider changes to I-5 sound wall.” Orange County Register, February 3, 2012, updated August 21, 2013. Swegles, F. "San Clemente to lodge complaints about I-5 wall." Orange County Register, December 21, 2011, updated August 21, 2013. Swegles, F., “A quest for peace and quiet,” Orange County Register, September 25, 2013. Tennessee Department of Transportation. 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. United States Code of Federal Regulations, Title 23: Highways - Part 772: Procedures for Abatement of Highway Noise and Construction Noise, June 2010. 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. Virginia Department of Transportation, Highway Traffic Noise Impact Analysis Guidance Manual (Version 4), Section 10.4 “Applications for Absorptive Noise Barriers,” August 6, 2013, pp. 32–33. Wisconsin Department of Transportation, Wisconsin Department of Transportation Facilities Development Manual, Chapter 23, Section 35 “Noise Abatement Measures.” February 15, 1988. Woodward-Clyde and Illingworth & Rodkin, Inc. Noise Abatement Evaluation: Interstate 580 Oakland, Reference 4-ALA-580, HP 311 Program. November 1999.

B-1 Phase 2 (Sound-Absorbing Barriers)— Detailed Analysis and Results A P P E N D I X B William Bowlby, Rennie Williamson, and Clay Patton BowlBy & AssociAtes, inc. Franklin, TN Judy Rochat, Jack Meighan, Shawn Duenas, and Keith Yoerg Ats consulting Pasadena, CA Ryan Haac and Ken Kaliski, Rsg White River Junction, VT

B-2 CONTENTS CHAPTER B-1.....................................................................................................................................B-3 Introduction to Appendix B................................................................................................................................... B-3 CHAPTER B-2.....................................................................................................................................B-4 Study Locations..................................................................................................................................................... B-4 CHAPTER B-3.....................................................................................................................................B-7 Results – I-75, Troy, Ohio (Location OH-1)............................................................................................................B-7 CHAPTER B-4................................................................................................................................... B-49 Results – I-70, South Vienna, Ohio (Location OH-2) ........................................................................................... B-49 CHAPTER B-5................................................................................................................................... B-93 Results – I-270, Grove City, Ohio (Location OH-3) .............................................................................................. B-93