Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts

State departments of transportation (DOTs) are required to consider highway traffic noise impacts from projects on existing and planned facilities. When these impacts exceed certain thresholds, 23 CFR 772 specifies a limited number of approaches to mitigate highway traffic noise. The most commonly used approach is noise barriers, which can be walls or, in some cases, earthen berms.  To date, some 3,000 miles of noise walls have been constructed along U.S. highways at an average cost of $2 million per mile of wall. However, noise walls are not always effective and appropriate. In some cases, a noise analysis indicates that a noise wall is not feasible and reasonable per 23 CFR 772. In other cases, a noise wall may provide only limited reductions of noise levels because of site conditions such as topography or traffic volumes. Even when a noise wall may provide an acoustical benefit, it may not meet cost-effectiveness criteria. Notably, noise regulations and policies only address mitigation through noise abatement, although common practice to address environmental issues is to avoid or minimize impacts, before considering mitigation. As a result, transportation agencies have no means to address highway traffic noise outside the regulatory process and are thus constrained to respond to community needs. Noise reduction targets established by policy or regulation can lead to situations where a transportation agency constructs a noise wall only for those portions of a community that qualify for abatement under regulatory requirements, while other portions of the same community receive no noise reduction benefit. Even if noise levels do not meet regulatory definitions of a noise impact, state DOTs and other transportation agencies may also seek to address complaints about/of excessive highway traffic noise. In addition, some communities may want reduced highway traffic noise, but oppose a noise wall. Conversely, communities may advocate for a noise barrier, although topography and other site conditions may mean that the barrier will function primarily as a visual screen and provide little reduction in noise. To address these limitations, transportation agencies have sought alternative approaches to highway traffic noise reduction. For example, quieter pavements can be useful in certain applications or in conjunction with traditional noise walls (see National Cooperative Highway Research Program (NCHRP) Report 738: Evaluating Pavement Strategies and Barriers for Noise Mitigation).  Rumble strips can be quieter using newer designs. However, climate and road maintenance practices can limit the use of these and other on-road design choices. There is some existing research into the effectiveness of right-of-way design elements. For example, the Ohio DOT has evaluated the noise reduction capability of small height (3'- 6') berms (see Acoustical Performance of Small Height Earthen Berms, OTP 1.2:Ac185/2018. Available at:, which are not appropriate or feasible for all locations or contexts. Research is needed to provide transportation agencies and their partners with information on how to avoid or reduce highway traffic noise using innovative approaches that are compatible with a wide range of contexts. This project will identify best practices and nontraditional and emerging approaches to increase design options for highway traffic noise solutions that are acceptable to adjacent communities and the transportation agency.    The objective of this research is to develop a resource of innovative approaches, beyond the use of noise barriers, to avoid and minimize highway traffic noise and address complaints. The resource should provide descriptions, ranges of noise reduction benefits, cost factors, and context-appropriateness for design choices and management strategies that may be adopted for other reasons, but that provide noise reduction co-benefits, as well as those adopted specifically to address noise. Task descriptions are intended to provide a framework for conducting the research. The NCHRP is seeking the insights of proposers on how best to achieve the research objective. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objective. Task 1. Provide an information and data collection plan. The plan will describe a strategy that will collect information of adequate detail and from diverse sources on a broad set of alternative approaches that can be used singly or in combination to avoid and/or reduce highway traffic noise. Approaches will include, but not be limited to:  (1) On-road design choices (a) Quieter bridge decks and joints (b) Quieter rumble strip design (c) Quieter pavements for travel lanes and/or shoulders (2) Highway design choices (a) Horizontal or vertical alignment (b) Solid safety barriers in lieu of guardrail (c) Separation zones between vehicle travel lanes and side paths for nonmotorized users (3) Right-of-way design elements (a) Low berms (b) Vegetation screens (c) Vegetated swales and retention basins (d) Sound-absorbing ground surface adjacent to the highway (4) Operations management strategies (a) Speed or truck restrictions (5) Approaches that can be implemented by subdivision developers, home owner associations, special districts, or local governments (6) Emerging or experimental approaches Task 2.  Provide a summary of alternative approaches. After executing the information collection plan, develop a summary to include: (1) Description of alternative approaches; (2) Information on the expected reduction in traffic noise as reported in the literature; and (3) Available information on construction and maintenance cost. Task 3. Develop ranges of traffic noise reduction for at least 3 approaches for which highway traffic noise modeling results are not previously reported.  (1) The ranges will be appropriate for use in the current, approved version of the Federal Highway Administration Transportation Noise Model (TNM) or for post-processing of results from TNM. (2) Collecting original field data for the modeling is not required; data from prior noise studies, the research literature, or other secondary sources may be adapted and used. Provide a technical memorandum describing the proposed modeling strategy and selected approaches for review by NCHRP.   Task 4. Provide the results of the approved modeling strategy along with documentation of the methodology and assumptions. Task 5. Provide an annotated outline of the final deliverables. The outline should describe the content, organization, and form of presentation. Task 6. Develop final deliverables. Anticipated final deliverables include: (1) Technical report describing the information and data collection effort, the modeling effort, and a set of prioritized future research needs; (2) Practitioner resource on alternative approaches including the results of the modeling effort; and (3) A PowerPoint presentation summarizing the project.


  • English


  • Status: Proposed
  • Funding: $250000
  • Contract Numbers:

    Project 25-57

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Hartell, Ann

  • Start Date: 20190305
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01672251
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 25-57
  • Files: TRB, RiP
  • Created Date: Jun 18 2018 3:03PM