Environmental Guidance Documents

NEPA Process Guidance for Federal Aid Projects


Federal-Aid Highway Act

The Federal-Aid Highway Act of 1972 requires FHWA to develop a noise standard for new federal-aid highway projects. The standard provides national criteria for all highway agencies but also gives state DOTs flexibility in managing highway traffic and construction noise. In addition to defining traffic noise impacts, the FHWA Noise Standard requires that noise abatement be considered when traffic noise levels that exceed a defined threshold are identified during noise analysis, planning and project design.

EPG provides technical expertise to evaluate noise impacts that may result from ADOT transportation projects. Specialized noise modeling is used for projects that increase traffic capacity or that have changes in the vertical and/or horizontal alignment of a roadway project.

Noise Abatement

FHWA regulations for noise evaluation are detailed in Title 23 CFR 772, Procedures for Abatement of Highway Traffic Noise and Construction Noise. The main objectives of 23 CFR 772 are "to provide procedures for noise studies and noise abatement measures, to help protect the public health and welfare, to supply noise abatement criteria, and to establish requirements for information to be given to local officials for use in the planning and design of highways approved pursuant to Title 23, United States Code (U.S.C.)." The regulations require the consideration of noise abatement mitigation when traffic noise impacts that exceed a defined threshold are identified.

The FHWA regulations require the following during the planning and design of a highway project:

  • Identification of traffic noise impacts and examination of potential mitigation measures
  • Incorporation of reasonable (resident/owner preferences, noise reduction goals, cost effectiveness) and feasible (engineering and acoustic) noise mitigation measures into the highway project
  • Coordination with local officials to provide helpful information on compatible land use planning and control

In addition, ADOT establishes the following goals when considering noise abatement:

  • Reduction of noise levels to 64 decibels or less
  • Effective aesthetic and architectural integration into the community
  • Public involvement
  • Careful attention to neighborhood issues like fire access, security, visibility, and drainage
  • Careful attention to driver safety, including line of sight and emergency vehicle access
NEPA Process

If traffic noise impacts are expected and sensitive receivers are present, the effects must be disclosed under the requirements of NEPA. According to FHWA noise abatement criteria, noise abatement measures must be evaluated and considered. EPG's noise specialists evaluate ADOT projects to ensure that all projects and operations comply with federal, state, and local noise abatement policies and regulations. Analysis of abatement measures includes right-of-way acquisition to provide a buffer zone, changes to horizontal and vertical alignment, insulation of some facilities if exterior noise abatement is not feasible, traffic management measures, and noise barriers. Preliminary noise barrier design includes considerations such as heights, lengths, and location. The noise abatement decision and the noise mitigation measures are incorporated into the environmental documentation.

The following flowchart demonstrates the process that is followed during noise modeling and documentation of the results:

Noise Modeling Process

Additional Information

Facts about Noise

Common Indoor and Outdoor Noise Levels



Current Noise Abatement Policy
This policy became effective on July 13, 2011 and should be utilized for all ADOT reviewed or approved construction projects for which the noise study was initiated on or after the policy’s effective date. Consult the EPG Air and Noise Team prior to utilizing this policy in the preparation of any noise analysis.

Appendix A 23 CFR 772 Final Rule

Appendix B Highway Traffic Noise Analysis and Abatement Guidance Revised January 2011

Appendix C Measurement of Highway-Related Noise

Appendix D Traffic Noise Study Report Format Guide

Superseded ADOT Noise Abatement Policy/Addendum
This policy is published solely for informational purposes and may only be utilized for those projects for which a noise study was initiated prior to July 13, 2011. Consult with the EPG Air and Noise Team prior to utilizing this policy in the preparation of any noise analysis for an ADOT-managed or approved project. This policy became effective on December 5, 2005.