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Analysis and Abatement Guidance

Appendix A: Highway Traffic Noise Analysis Process

There is no one size fits all approach to the level of analysis necessary for various levels of environmental documents. One project may result in significant impacts on the natural environment, have no noise impacts and require an EIS, while another project processed as a CE may not have any significant impacts, but has numerous noise impacts. Various approaches to NEPA among States with programmatic agreements with the FHWA may also result in similar projects processed as different environmental documents in different States. The information below is a general guide to the level of documentation needed, but State approaches may vary.

Highway Traffic Noise Analysis

The level of detail and effort for the highway traffic noise analysis required for each alternative of a proposed project should be commensurate with the type of project and the impacts and/or issues with which it is associated. 23 CFR 772.11 and .13 provide the general content of a highway traffic noise analysis.

The major objectives of a highway traffic noise study for new highway construction or a highway improvement are:

  1. To identify areas of potential highway traffic noise impact for each study alternative;
  2. To determine existing noise levels;
  3. To predict future noise levels and identify impacts;
  4. To evaluate abatement measures for these impacts
  5. To compare the various study alternatives based on predicted highway traffic noise impacts and the associated social, economic and environmental effects of abatement.

Highway traffic noise studies provide information primarily to government decision makers and the lay public. For the government decision maker, the study should provide a portion of the data needed for the informed selection of a satisfactory project alternative and appropriate abatement measures. For the lay public, the study should provide discussion of potential impacts in any areas of concern to the public.

Identifying Activity Categories and Applicable NAC of Adjacent Land Uses

The first step in the highway traffic noise study is to determine the activity category and applicable NAC for all land uses adjacent to each project alternative. Select representative locations for all activity categories to determine existing and future noise levels.

Determine status of undeveloped lands. Consider permitted land as developed for the purposes of the noise analysis. Assign the appropriate activity category to the permitted land and assess highway traffic noise impacts accordingly.

Determination of Existing Highway Traffic Noise Levels

Establish existing highway traffic noise levels by field measurements for all developed and permitted land uses and activities. Field measurements are preferred because existing noise levels are usually a composite of environmental noise sources and highway traffic noise prediction models are applicable only to noise originating from a specific source. If it is clear that existing noise levels at locations of interest are predominantly due to a highway, calculate existing noise levels using the FHWA Traffic Noise Model (TNM).

When making existing noise measurements consider the following:

  1. Time of day, e.g., peak hour vs. any other time of day;
  2. Day of week, e.g., weekend day vs. work day;
  3. Week of year, e.g., tourist season vs. off-season;
  4. Representativeness of the noise, and
  5. Extenuating circumstances that may alter noise levels, e.g. construction

Twenty-four hour noise measurement may help determine the loudest traffic hour. The measurement should yield the worst hourly highway traffic noise level generated from representative noise sources for that area. The period with the highest sound levels may not be at the peak traffic hour but instead, during some period when traffic volumes are lower but the truck mix or vehicle speeds are higher. Measurements should be made at representative locations - that is, residential neighborhoods, commercial and industrial areas, parks, places of worship, schools, hospitals, libraries, etc.

Representativeness relates to the noise typically found in a given location. Aircraft noise is usually representative near an airport but not in areas having no airport; the noise from barking dogs is usually representative near kennels but not in a residential neighborhood; and the noise from ambulance or police sirens is usually representative near hospitals or police stations but not in other locations.

Prediction of Future Highway Traffic Noise Levels

23 CFR 772 requires use of the FHWA TNM to predict future highway traffic noise levels for Federal or Federal-aid projects.

Pavement Types

The FHWA TNM contains four pavement types to select from when developing a model run. There are three generalized individual pavement types and an "Average" pavement type. The three individual pavement types are: dense graded asphalt (DGAC), open graded asphalt (OGAC), and Portland cement concrete (PCC). "Average" pavement type is a combination of DGAC and PCC. Each individual pavement type is associated with vehicle source noise emission levels (source levels) measured along highways with the corresponding pavement type.

"Average" pavement type is the default pavement type in the FHWA TNM to predict existing and future noise levels. Per 23 CFR 772.9(b), all highway agencies must use "Average" pavement type unless they obtain FHWA approval to use another pavement type for predicting future noise levels.

Pavement Type When Predicting Existing Highway Traffic Noise Levels:

When using the FHWA TNM to predict existing highway traffic noise levels, users may select one of the FHWA TNM-defined pavement types to predict the existing highway traffic noise conditions. The selection of an individual pavement type in the prediction of existing highway traffic noise levels is optional to highway agency's to implement and should only be done in conjunction with taking measurements of existing levels. If the highway agency does not opt to use an individual pavement type, then it must use "Average" pavement type in their prediction of existing highway traffic noise levels. Highway agencies may opt to use one of the FHWA TNM defined (individual) pavement types when predicting existing highway traffic noise levels on a project-by-project basis, if clearly stated in the highway agency's noise policy, environmental documents and noise analysis documents.

Identification and Consideration of Highway Traffic Noise Abatement

The next step in the highway traffic noise analysis is comparison of the various study alternatives based on predicted highway traffic noise impacts and the associated social, economic and environmental effects of abatement.

It is FHWA's policy to ensure that projects incorporate all feasible and reasonable abatement measures to minimize highway traffic noise impacts to the extent practicable. Highway agencies must fulfill this commitment to minimize highway traffic noise impacts through prudent application of FHWA's highway traffic noise regulation and the State noise policy.

23 CFR 772.13(g) requires that "...before adoption of a final environmental impact statement or finding of no significant impact, the highway agency shall identify highway traffic noise abatement measures which are feasible and reasonable and which are likely to be incorporated in the project...." This is frequently the most difficult part of the highway traffic noise analysis for a proposed highway project. Highway agency decision makers often ask, "What does feasible and reasonable mean? How should we determine feasibility and reasonableness?" The following discussion assists in answering these questions.

Feasibility and Reasonableness Determination and Worksheet

Each highway agency should develop its own factors under both the feasibility and reasonableness criteria. Keeping in mind that the following are required factors:

  1. Feasibility: At least a 5 dB(A) highway traffic noise reduction is achieved at the majority of the impacted receivers.
  2. Reasonableness: Point of view of benefitting property owners and residents
  3. Reasonableness: Allowable cost of highway traffic noise abatement
  4. Reasonableness: Meets or exceeds the reasonable design goal

The report must provide thorough documentation of the feasibility and reasonableness analysis. Each highway agency should develop a worksheet to evaluate feasibility and reasonableness. Please see Appendix D for an example feasibility and reasonableness worksheet.

Construction Noise Analyses

The highway agency must address consideration of construction noise in the environmental document. A construction noise documentation example is in Appendix B - Highway Traffic Noise Reporting.

Coordination with Local Governments

The final part of the highway traffic noise analysis is coordination with local officials whose jurisdictions are affected. The primary purpose of this coordination is to promote compatibility between land development and highways.

The highway agency should also coordinate with the local governments when the local governments are opposed to the recommended noise abatement that was determined to be feasible and reasonable. This coordination should determine if the local government's reasons for the opposition are justified, such as for safety reasons. The local governments cannot arbitrarily veto and/or restrict the length or height of the mitigation measure that was determined to be feasible and reasonable based on an unjustified reason such as visual quality. The FHWA will determine if the justification is arbitrary (e.g. visual, aesthetics, inappropriate use of safety, etc.). If the justification is arbitrary, then the FHWA will not authorize the Federal-aid project unless the recommended noise abatement is included.

The highway agency should furnish the following information to appropriate local governments for all Federal-aid highway projects:

Federal-aid Highway Projects Involving Other Modes of Transportation

Highway traffic noise analyses should include noise from all sources. The reasonableness of providing highway traffic noise abatement for identified impacts should include consideration of the ability to abate the noise from all sources, not just highway traffic noise. Highway traffic noise analysis may sometimes involve noise emanating from more than one mode of transportation - that is, the analysis may include aircraft noise and/or rail/transit noise. For this type of analysis, use an Ldn noise descriptor to combine the noise levels from all the sources.

If the analysis is for a Federal-aid highway project, Federal Highway Administration noise requirements apply. The existing noise levels should include all the representative noise sources. The FWHA TNM limits consideration of existing noise levels to highway sources; however, analysts should consider other major noise sources, including other transportation sources, when designing noise abatement. Failure to account for other environmental noise may result in ineffective noise abatement.

Aircraft Noise

Calculate aircraft noise using the Federal Aviation Administration's Integrated Noise Model.

Rail Noise

If a highway project includes a rail line, calculate the rail noise levels using the procedure outlined in the FHWA document entitled: "Advanced Prediction and Abatement of Highway Traffic Noise, June 1982". Highway traffic noise levels should be converted from Leq(h) to Ldn using the procedure outlined in the above referenced document. Impacts should be identified using FHWA's two impact criteria, assuming Ldn=Leq(h), and the feasibility and reasonableness of any potential abatement measures should be determined considering all the sources of noise.

If a noise analysis is being done for a railroad project, the Federal Railroad Administration's (FRA) "Guidance on Assessing Noise and Vibration Impacts" should be should be referenced for appropriate requirements and analysis procedures. This guidance is at: http://www.fra.dot.gov/Page/P0216.

Transit Noise

Calculate transit noise using the Federal Transit Administration (FTA) noise requirements. The analysis should follow the procedures contained in the FTA's Transit Noise and Vibration Impact Assessment Guidance, dated May 2006. This document is at: http://www.fta.dot.gov/documents/FTA_Noise_and_Vibration_Manual.pdf.

Updated: 03/06/2013
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