127.13 Noise

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Key Points


127.13.1 Introduction

127.13.1.1 Overview

The Federal Aid Highway Act of 1970 mandates that federal agencies consider the impact of their activities on nearby land uses. The act applies to all federal projects including those with National Environmental Policy Act (NEPA) classifications as Categorical Exclusions (CEs). The act requires FHWA and MoDOT to evaluate every project and determine whether it could have a negative impact on nearby residences or other noise-sensitive receptors.

Sound (noise) occurs when an ear senses pressure variations or vibrations in the air. Noise is unwanted sound. A person’s brain relates a subjective element to a sound, and an individual reaction is formed. Studies indicate that the most pervasive sources of noise in our environment today are those associated with transportation. Highway traffic noise tends to be a dominant noise source in both the urban and rural environment.

Public concern about noise led to federal legislation in 1970 that authorized the use of federal-aid highway funds for measures to abate and control highway traffic noise. MoDOT has a federally approved traffic noise policy to define and conform to the requirements of Title 23, Article 772, Code of Federal Regulations (23 CFR 772), and the noise-related requirements of the 1969 NEPA. The guidelines in the MoDOT Noise Policy are used to determine the need, feasibility, and reasonableness of noise abatement measures and provide the basis for statewide uniformity in traffic noise analysis.

127.13.1.2 Laws and Regulations

  • The National Environmental Policy Act (NEPA) of 1969—provides broad authority and responsibility for evaluating and mitigating adverse environmental effects, including highway traffic noise, and directs the federal government to use all practical means and measures to promote the general welfare and foster a healthy environment.
  • 23 USC 109(h), Federal-Aid Highway Act of 1970—mandated that FHWA develop noise standards for mitigating highway traffic noise.
  • 23 CFR 772, Procedures for Abatement of Highway Traffic Noise and Construction Noise—the FHWA regulations for mitigation of highway traffic noise in the planning and design of federally aided highways require conducting a noise analysis.

127.13.1.3 Process

The FHWA regulations require MoDOT to a) identify traffic noise impacts and examine potential mitigation measures; b) incorporate reasonable and feasible noise mitigation measures into its highway projects; and c) coordinate with local officials to provide helpful information on compatible land use planning and control during the planning and design of a highway project. The regulation makes a distinction between projects for which noise abatement is considered as a feature in a new or expanded highway and those for which noise abatement is considered as a retrofit feature on an existing highway. The former are defined as Type I projects, the latter as Type II. The district must establish the need for a noise analysis by determining whether a proposed project is a Type I or a Type II project in regard to noise abatement.

Project Definition
Type I project A proposed federal or federal-aid highway project for the construction of a highway on new location or the physical alteration of an existing highway that significantly changes either the horizontal or vertical alignment or increases the number of through-traffic lanes. The consideration of noise abatement as part of the highway construction project is mandatory if federal-aid funds are to be used and if a traffic noise impact is expected to occur.
Type II project A proposed federal or federal-aid highway project for noise abatement as a retrofit feature on an existing highway. MoDOT does not generally construct these types of projects.


If the project is determined to be Type I, an appropriate noise analysis is required. The traffic noise analysis, performed by a consultant, includes the following for each alternative under detailed study:

  • identify existing activities, developed lands, and undeveloped lands for which development is planned, designed, and programmed that may be affected by traffic noise from the highway
  • determine existing noise levels
  • predict future traffic noise levels for highest noise level in design year by the Traffic Noise Model (TNM), nomograph, or FHWA-approved method
  • determine any traffic noise impacts
  • evaluate any alternative noise abatement measures for reducing or eliminating the traffic noise impacts.

If no noise impacts are identified, document the findings and conclude the analysis. If noise impacts are identified, consider noise abatement measures. If abatement measures are not considered reasonable and feasible, conclude the study. If abatement is reasonable and feasible, document the results of the analysis, including the likelihood of abatement measures and identification of impacts for which no apparent solution is available. Districts will hold informational meetings and public hearings will be conducted for potential property owners who may be affected by traffic noise impacts.

MoDOT does not generally construct Type II projects since they receive no federal funding.


127.13.2 Project Development Milestones

127.13.2.1 Initial Screening Stage

At the initial project screening stage, if maps and right-of-way/easement information are available, district personnel determine whether a noise analysis is required. Details of this process are described in 127.13.1.3 Process.

127.13.2.2 Location/Conceptual Plan Stage

At the location/conceptual plan stage, if traffic noise has not yet been evaluated and total, new right-of-way and easement acreages are available, district personnel would again determine whether a noise analysis is required (detailed in 127.13.1.3 Process) for the project.

For projects that require an Environmental Assessment (EA) or an Environmental Impact Statement (EIS), the environmental compliance manager and the district will coordinate on when to begin this process. The district may be required to engage an outside consultant to conduct the noise analysis.

127.13.2.3 Preliminary Plans Stage

At the preliminary plans stage, if traffic noise has not yet been determined, district personnel, or an outside consultant will prepare a noise analysis report (detailed in 127.13.1.3 Process) for the project. At any planning stage in the design of the project when it is determined that noise mitigation is warranted, the mitigation design will commenced.

127.13.2.4 Right of Way Plan Stage

At the right-of-way plan stage, if traffic noise has not yet been determined, district personnel, or outside consultant will prepare a noise analysis report (detailed in 127.13.1.3 Process) for the project.

127.13.2.5 Final Design Stage

At the final design stage, if traffic noise has not yet been determined, district personnel, or an outside consultant will prepare a noise analysis report (detailed in 127.13.1.3 Process) for the project.

127.13.2.6 Letting

At this stage, if traffic noise has not yet been determined, district personnel or an outside consultant will prepare a noise analysis report (detailed in 127.13.1.3 Process) for the project.

127.13.3 Construction Noise

The public often views highway construction noise as a short term, necessary price for growth and improvement. Highway construction noise should generally be addressed in a qualitative, rather than quantitative, manner commensurate with the scope of the highway project. Construction noise levels may be predicted, if warranted by public comment. If potential construction noise impacts are identified, a common sense approach should be utilized to incorporate appropriate abatement measures into the highway project.