Companion Guide to Video August 2012

www.fhwa.dot.gov/federal-aidessentials

Local public agencies may encounter several 

areas of environmental law on a Federal-aid 

project. These areas address a project's effects 

on:

• The natural environment—including air 

and water quality, wetlands, wildlife, or 

endangered species

• The social environment—meaning 

elements that affect our quality of life

• Historic sites

• Parks and recreation areas

The National Environmental Policy Act, known as 

NEPA, provides a framework for environmental 

analyses, reviews, and a series of consultations. 

NEPA's process "umbrella" covers a project's 

compliance with all pertinent Federal 

environmental laws.

While NEPA provides a coordinated environmental 

review process, the related environmental law 

specifies what an agency must do to comply with 

its particular requirements, which can vary widely.

For example, when agencies use Federal-aid 

funds to build or substantially alter a highway, 

known as a Type 1 project, they must study the 

potential effects of unwanted or excessive 

highway traffic noise.

If the study determines there will be an impact to a 

noise sensitive area, agencies must also evaluate 

measures to lessen the noise. 

Let's take a look at steps agencies 

typically take when considering 

noise impacts from a project.

To start, agencies first determine if a noise impact 

will occur. To do that, a qualified employee or 

consultant conducts a noise study. Noise studies 

compare the existing conditions along the project 

corridor with predicted future noise levels resulting 

from your project. Studies also consider the 

existing and planned land use and the levels of 

noise appropriate for that use as defined in the 

Noise Abatement Criteria table, or NAC table. 

Environment

Other Laws and Requirements

Highway Traffic Noise

Assessing highway traffic noise is an important consideration on 

Federal-aid projects
Federal-aid Essentials for Local Public Agencies

The NAC table lists the abatement noise levels for 

selected land uses and is contained the highway 

traffic noise regulation. 

A traffic noise impact occurs when the predicted 

future traffic noise levels approach or exceed the 

noise abatement criteria. For example, a noise 

impact will occur for residential land use when the 

predicted future traffic noise level of 68 decibels 

exceeds the 67 decibels listed in the Noise 

Abatement Criteria table. 

A traffic noise impact also occurs when the 

predicted future traffic noise levels substantially 

exceeds the existing noise levels. The criteria for 

substantially exceeds is contained in each State’s 

traffic noise policy. 

If the study predicts that no impact will occur, the 

study is completed and shared with land use 

planning officials.

But if the study predicts a noise impact will occur, 

the noise specialist will evaluate noise abatement 

measures that would substantially reduce the 

highway noise. 

Road realignment, earthen berms, and noise walls 

are examples of noise abatement measures.

Federal Highway Administration (FHWA)

regulations require agencies to implement noise 

abatement measures that are both feasible and 

reasonable. The criteria for feasible and 

reasonable are contained in each State’s traffic 

noise policy.

The long-term solution to unwanted highway noise 

is to restrict or prevent residential and other noisesensitive land use near highways. Agencies can 

help avoid future problems by coordinating with the 

officials responsible for land use planning and by 

sharing the results of traffic noise studies. 

To illustrate the process, let’s 

consider a project that will add 

multiple lanes to an existing 

highway.

A traffic noise consultant identifies existing land 

uses and noise levels by visiting the project area 

and reviewing the project’s engineering plans and 

land use maps. The consultant discovers the 

corridor is a highly developed residential area with 

multiple, single-family dwellings. 

The consultant determines that existing traffic noise 

levels are 62 decibels for the ten residences 

adjacent to the existing highway. Using 

sophisticated modeling tools, the consultant 

anticipates that future noise levels at the same 

location will be 69 decibels. 

The 69 decibels exceeds the noise abatement 

criteria for residential land use by two decibels and 

the State’s traffic noise policy requires an 

evaluation of mitigation measures.

The consultant proposes and evaluates the 

effectiveness of a noise wall. 
Federal-aid Essentials for Local Public Agencies

The noise wall will reduce future noise levels by an 

average of 10 decibels and is estimated to cost 

$100,000. The cost-to-benefit ratio is $10,000 per 

residence. Following the State’s guidelines for 

noise abatement, this mitigation measure is 

determined to be both feasible and reasonable. 

A design engineer adds to the plans a 300-footlong by 10-foot-high noise wall and the agency 

sends a letter to the county planning office 

notifying it of the results of the study.

If your agency plans to use Federalaid to build or substantially alter a 

highway, your agency will need to 

conduct a traffic noise study and 

coordinate with land use planning 

agencies.

To determine the criteria your State department of 

transportation will apply to determine if a noise 

impact will occur and when and how to abate traffic 

noise, consult your State’s noise policy. Traffic 

noise specialists and consultants will also find 

valuable technical guidance in FHWA’s Highway 

Traffic Noise Analysis and Abatement Policy.
Federal-aid Essentials for Local Public Agencies

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• Federal regulation covering procedures for abatement of highway traffic and 

construction noise

http://www.gpo.gov/fdsys/pkg/CFR-2011-title23-vol1/pdf/CFR-2011-title23-

vol1-part772.pdf

• FHWA guidance for applying Federal regulation on traffic noise analysis and 

abatement 

http://www.fhwa.dot.gov/environment/noise/regulations_and_guidance/analy

sis_and_abatement_guidance/

• Information on highway traffic noise problems and information on planning 

and construction of traffic noise barriers

http://www.fhwa.dot.gov/environment/noise/regulations_and_guidance/probr

esp.cfm

• Link to FHWA’s Noise Barrier Design Handbook with information on 

materials, installation techniques and costs

http://www.fhwa.dot.gov/environment/noise/noise_barriers/design_constructi

on/design/index.cfm