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Evaluating Pavement Strategies and Barriers for Noise Mitigation (2013)

Chapter: Chapter 1 - Background and Research Approach

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Suggested Citation:"Chapter 1 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2013. Evaluating Pavement Strategies and Barriers for Noise Mitigation. Washington, DC: The National Academies Press. doi: 10.17226/22541.
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Suggested Citation:"Chapter 1 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2013. Evaluating Pavement Strategies and Barriers for Noise Mitigation. Washington, DC: The National Academies Press. doi: 10.17226/22541.
×
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Suggested Citation:"Chapter 1 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2013. Evaluating Pavement Strategies and Barriers for Noise Mitigation. Washington, DC: The National Academies Press. doi: 10.17226/22541.
×
Page 5
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Suggested Citation:"Chapter 1 - Background and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2013. Evaluating Pavement Strategies and Barriers for Noise Mitigation. Washington, DC: The National Academies Press. doi: 10.17226/22541.
×
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3 Background In the past decade, considerable interest in quieter pavement technology has been shown by state and local transportation agencies, the Federal Highway Administration (FHWA), and the general public. This interest has been advanced by a num- ber of research and pilot projects that have demonstrated traffic noise reductions over existing pavements by the application of quieter pavement overlays and surface texture modifications. These reductions have been documented both with objective noise measurements and the reaction of the public to the quieter pavements. In addition, the understanding of quieter pavements in the United States has increased dramatically in this time period particularly by the advent of the on-board sound intensity (OBSI) method of quantifying the tire noise performance of these pavements at the source (1, 2, 3, 4). With this knowledge and interest, the potential for quieter pavements to be used as alternatives or supplements to traditional barriers for traffic noise abatement has been considered. On the surface, a comparison of barriers and quieter pave- ment appears to be straightforward. Initially, barriers typically cost more to build than using quieter pavement and the reduc- tion in traffic noise at receptor locations can be comparable depending on the existing noisier pavement and the height of the barrier (5). Over time, however, the noise performance of quieter pavements degrades resulting in less noise reduc- tion and higher traffic noise levels. To maintain the noise per- formance of the quieter pavement, the pavement will need to be replaced or treated, possibly at a faster rate than typically required for rehabilitation. As a result, there may be higher long-term recurring costs associated with using quieter pave- ment for noise reduction than would be incurred for a noise barrier. For barriers, the amount of noise reduction defined by the insertion loss of the barrier is generally invariant with time and requires little, if any, additional cost to main- tain its performance over time. Because of the difference in the performance-maintenance requirements of these two approaches, methodologies need to be developed for compar- ing these two noise abatement or reduction options beyond the initial costs. Other issues add to the complexity of comparing barriers and quieter pavement. Maintaining reduced noise levels with quieter pavement will require periodic acoustic rehabilitation of the pavement to achieve a specific range of traffic noise levels at the receptors, assuming constant traffic volumes and con- ditions. For barriers, although the amount of noise reduction remains unchanged if the traffic mix does not change, the traf- fic noise levels will still increase by an unspecified amount as the pavement ages. Also, for many highway projects, barriers are often a local solution not extending the entire length of the project. However, the same pavement type is generally con- structed throughout the project and local solutions may not be practical. Further, in some cases, barriers may not provide sufficient insertion loss to be considered, may not be physi- cally possible, may not provide noise reduction to a sufficient number of the receptors to be viable, or may not be desired by the community. In these situations, quieter pavement may provide some amount of noise reduction. FHWA Policy In 1997, Title 23, Part 772, of the Code of Federal Regula- tions (23 CFR 772) required that for Federal-Aid highway projects, noise analysis must be performed for specific types of projects when potentially impacted receptors are present. This regulation identified five noise abatement options and required that the selected abatement be both feasible and reasonable. In 2010, 23 CFR 772 was updated and published on July 13 for implementation by state agencies 1 year later (6). The updated version of 23 CFR 772 incorporates some of the information and definitions that were included in the original 1995 “Highway Traffic Noise Analysis and Abate- ment Policy and Guidance” (7). To support the update of 23 CFR 772, the document “Highway Traffic Noise: Analysis C H A P T E R 1 Background and Research Approach

4and Abatement Guidance” was initially released in June 2010 and revised in January 2011 (8). The revised policy includes changes that affect abatement measures and analysis, but the basic approach remains. The five approved methods of noise abatement remain the same and exclude the use of pavement as an abatement option. In practice, barriers will likely remain the primary method of abating traffic noise (9). However, the use of pavement types other than FHWA Traffic Noise Model (FHWA TNM®) Average Pavement can now be considered in the analysis, upon documentation and approval by FHWA through the Quieter Pavement Pilot Pro- gram process. In regard to evaluating noise abatement options, the con- cept of feasibility remains essentially the same as in the ear- lier 23 CFR 772; however, some changes were incorporated in the new policy. Barriers or other methods are not feasible if they do not reduce predicted noise levels by 5 dB or more for some number of impacted receptors where the number is now defined by the highway agency noise policy (6). Feasibility also continues to include the physical ability to be built from an engineering perspective. Reasonableness of noise abatement continues to consider the cost of abatement relative to the number of benefited receptors and the view of affected residents as well as other circumstances. However, newly added to reasonableness cri- teria is the noise reduction design goal. This provision man- dates that agencies establish the noise reduction design goal between 7 and 10 dB for the minimum amount of noise reduc- tion produced by the abatement. The abatement must meet or exceed this goal for some number of benefited receptors in order to be considered reasonable. Although the noise reduc- tion design goal does not replace the acoustic feasibility cri- terion of 5 dB with 7 to 10 dB, it can have this effect in some cases when the barrier is feasible but does not achieve at least 7 to 10 dB for some benefited receptors. Another change in 23 CFR 772 was the requirement that highway agencies define the threshold of noise reduction, which determines a benefited receptor, as a reduction of not less than 5 dB. Previously, the threshold varied by state over a range of 3 to 6 dB with one state using 6 dB for the first row of receptors and 4 dB for the second. Other Considerations The tire noise performance of the pavement used in TNM corresponds to an average of the performance of pavements that was determined from statistical pass-by (SPB) measure- ments documented in the FHWA Reference Energy Mean Emission Levels (REMEL) database (10). For the purposes of this research project, pavements were grouped into three categories: portland cement concrete (PCC), dense-graded asphalt concrete (DGAC), and open-graded asphalt concrete (OGAC). Averages of SPB data for PCC and DGAC pavements were formed for different vehicle categories. This “Average Pavement” type is used in TNM traffic noise predictions as required by 23 CFR 772. During the course of this research, the FHWA, through the Volpe National Transportation Systems Center, was conduct- ing a study to identify potential methods of incorporating pavement-specific tire noise performance into TNM (11). These methods included adjustment of the tire source lev- els based on OBSI data combined with accounting for pave- ment sound absorption, expanding the REMEL database to include pavement types to be used in TNM, or applying post- calculation corrections to the model results. The first report on FHWA’s study demonstrated and concluded that “using OBSI data is a valid option for incorporating a broad range of pavement effects in the FHWA TNM” (12). This approach is very attractive for application in methodologies for evaluat- ing pavement strategies and barriers in noise abatement for several reasons. First, it allows a state highway agency (SHA) to input the actual tire noise source levels for the pavements it is considering in a project rather than a nationwide aver- age that may or may not be appropriate to the state. Second, it allows the prediction of changes in traffic noise levels if the tire noise performance of the quieter pavement changes over time. Third, it properly spatially locates the region where noise source strength changes, allowing more accurate propa- gation modeling. For these reasons, the use of OBSI in TNM became a significant element of the methodology developed in this research. Also during the course of this research, the standardiza- tion of OBSI for measurement of the tire noise performance of pavements progressed sufficiently to be considered as a method that could be used by any SHA. In 2011, the Ameri- can Association of State Highway and Transportation Officials (AASHTO) TP 76 OBSI procedure (4) completed its 11th round of revision as a provisional standard and further substantive changes are not expected. Also NCHRP Project 1-44(1), “Mea- suring Tire–Pavement Noise at the Source: Precision and Bias Statement,” was completed and the final report is now avail- able (13). The results of NCHRP 1-44(1) further quantified the uncertainty produced by measurement variables, rec- ommended more controls, and established expected preci- sion and bias values. Research Objective The objective of this research was to develop a method- ology for evaluating the feasibility, reasonableness, effective- ness, and longevity of acoustic and economic features of

5 pavement strategies and barriers used for noise mitigation of highway traffic noise. The approach used to accomplish this objective is described in this chapter. The need for this research was driven by (1) the complex- ity of evaluating both barriers and quieter pavement on an “equal playing field” for use by state and local agencies and (2) the need to develop a methodology that can be used in making such evaluations independent of policies. Research Approach The intent of the research was explicitly not to develop or propose changes to federal policy but to develop a methodol- ogy that can be adapted into FHWA policy in a manner that the agency could define at a later time if desired. Therefore, the basic framework of 23 CFR 772 was considered in this research, particularly in regard to feasibility and reasonable- ness. Also, the case studies used to illustrate application of the proposed methodology considered state agency policies developed to meet the older version of 23 CFR 772. To accomplish the project objective, the research included the following four tasks: 1. Collect and review information. Information regarding existing methodologies for evaluating the feasibility, rea- sonableness, effectiveness, and longevity of acoustic and economic features of both pavement and barriers was gath- ered and reviewed. Initially, this information was divided into several specific topics including pavement acoustic longevity, barriers, cost–benefit, life-cycle cost analysis (LCCA), noise policies, and the FHWA TNM implemen- tation. As it became apparent that sound absorption by the pavement could also influence the predicted noise level, the category of effective flow resistivity was added. In this task, over 130 sources of information were identi- fied and more than 60 of these were further reviewed and referenced. 2. Identify and evaluate methodologies and issues. The information collected and reviewed in Task 1 was evaluated and summarized and specific issues were identified as con- siderations for defining and potentially implementing the methodologies. Each aspect of the identified methodolo- gies was examined in detail. For feasibility, technical acous- tic issues considered the relationship between OBSI and wayside measurements and TNM predictions, the noise reduction provided by both barriers and quieter pavement as a function of distance, and the additional noise reduc- tion provided by porous, sound-absorbing pavements. For reasonableness, different strategies were evaluated includ- ing quieter pavement alone, barriers alone, and combined barriers and quieter pavement. Aspects of effectiveness were explored to develop a definition of this term in regard to traffic noise, particularly in comparison to feasibility. For longevity, the limited available studies were reviewed and issues regarding collecting longevity data identified. For economic comparisons, cost–benefit analysis was consid- ered but LCCA was regarded as a more fair method for comparing the costs of pavement and barrier solutions. This work provided an overall approach for developing the methodology in Task 3. 3. Develop the methodology. The analysis performed in Task 2 was used to develop the initial proposed method- ology. The methodology included the use of OBSI data to quantify the noise levels of existing and future pavement projects and to assess the pavement acoustic performance over time. These data were used in the modified version of TNM to determine current and future noise levels for comparison to noise levels abated by barriers. These TNM results were then used to analyze feasibility and reason- ableness in a manner similar to 23 CFR 772. A dimension of effectiveness was introduced based on the resulting predicted level of traffic noise. Economic features were evaluated using an LCCA that takes into account the ini- tial cost of abatement and the cost of maintaining that performance over the life of the project. 4. Demonstrate applications of the methodology. The pro- posed methodology was applied to several example cases. One case involved a simple, flat highway geometry to illus- trate use of the methodology in an idealized case. Other case studies considered actual highway projects from sev- eral states and scenarios involving quieter pavement only, barriers only, and combined pavement and barrier. These scenarios were evaluated for feasibility, reasonableness, effectiveness, acoustic longevity, and economic features. The methodology was refined based on the findings of these case studies. Report Organization The report consists of six chapters and a list of references. Chapter 1 describes the background and research approach. Chapter 2 reviews how the existing process for highway traf- fic noise analysis is proposed to be modified with the inclu- sion of OBSI measurements and the use of LCCA. Chapter 3 addresses the evaluation parameters of highway traffic noise analysis, including feasibility, reasonableness, and effective- ness. Chapter 4 develops a scenario of new highway construc- tion and presents how the proposed analysis and evaluation parameters would be applied to three examples based on this scenario. Chapter 5 applies the analysis and evaluation

6methodology to actual highway projects in three states and presents the findings. A summary and suggestions for further research are presented in Chapter 6. Eight appendices to the report are available on the TRB website (http://www.trb.org/Main/Blurbs/169200.aspx). Appendix A explores the effect of porous, sound-absorptive pavement on traffic noise and its prediction. Appendix B provides an overview of pavement LCCA as implemented by FHWA and Appendix C illustrates the application of LCCA to a hypothetical situation involving a new highway project. Appendix D discusses feasibility, reasonableness, the new evaluation parameter of effectiveness, and the results of the supporting literature search. Appendix E provides information on the acoustic longevity performance of different pavements and Appendix F summarizes findings on the economic fea- tures and cost–benefit analysis. Appendices G and H provide detailed information on the LCCA performed for two highway widening projects.

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 738: Evaluating Pavement Strategies and Barriers for Noise Mitigation presents a methodology for evaluating feasibility, reasonableness, effectiveness, acoustic longevity, and economic features of pavement strategies and barriers for noise mitigation.

The methodology uses a life-cycle cost analysis to examine the economic features of mitigation alternatives, the FHWA Traffic Noise Model to integrate the noise reduction performance of pavements and barriers, and on-board sound intensity measurements as an input to the prediction model.

The appendixes contained in the research agency’s final report provide elaborations and detail on several aspects of the research. The appendixes are not included with the print version of the report, but are available online.

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