HIGHWAY TRAFFIC NOISE

IN THE UNITED STATES

Problem and Response 

U.S. Department of Transportation 

Federal Highway Administration 

April 2006
TABLE OF CONTENTS 

PAGE NO.

LIST OF TABLES

INTRODUCTION 1 

- Purpose 1 

- The Highway System 1 

- The Federal/State Relationship 2 

- Federal Participation in the Cost of Projects 2 

THREE-PART APPROACH TO HIGHWAY NOISE ABATEMENT 3 

- Land Use Planning and Control 3 

- Source Control 3 

- Highway Project Noise Mitigation 5 

 

FHWA NOISE ABATEMENT PROCEDURES 6 

- Noise Descriptors 6 

- Impact Criteria 6 

- Existing Activities 7 

- Type I/Type II Projects 7 

- Noise Analysis 7 

- Federal Participation 8 

- Noise Abatement 8 

- Coordination with Local Officials 10 

- Traffic Noise Prediction 10 

- Construction Noise 10 

NOISE BARRIERS CONSTRUCTED OR PLANNED 11 

- Noise Barriers Constructed 11 

- Effectiveness 14 

- Public Perception 14 

- Research Efforts 14 

SUMMARY 15 

APPENDIX

23 CFR Part 772 - Procedures for Abatement of Highway Traffic Noise and 

Construction Noise 
LIST OF TABLES 

PAGE NO.

1. Road Ownership in the United States 1 

2. Classification of Roads by Functional System 2 

3. Maximum Noise Emission Levels as Required by EPA for 4 

Newly Manufactured Trucks with GVWR Over 

10, 000 Pounds 

4. Maximum Noise Emission Levels as Required by EPA for In-Use 4 

Medium and Heavy Trucks with GVWR Over 10, 000 Pounds 

Engaged in Interstate Commerce 

5. Noise Barrier Construction by State 12 

6. Total Noise Barrier Length by Material Type 13 

7. States That Have Not Constructed Noise Barriers to Date 13 

8. Barrier Attenuation 14 

9. Noise Abatement Criteria (NAC) Hourly A-Weighted 21 

 Sound Level - decibels (dBA) 
INTRODUCTION

Noise, defined as unwanted or excessive sound, is an undesirable by-product of our modern way 

of life. It can be annoying, can interfere with sleep, work, or recreation, and in extremes may 

cause physical and psychological damage. While noise emanates from many different sources, 

transportation noise is perhaps the most pervasive and difficult source to avoid in society today. 

Highway traffic noise is a major contributor to overall transportation noise. A broad-based effort 

is needed to control transportation noise. This effort must achieve the goals of personal privacy 

and environmental quality while continuing the flow of needed transportation services for a 

quality society. 

Purpose

This report has been developed to provide information about the problem of highway traffic 

noise and the United States' response to that problem. This report summarizes 1) the general 

nature of the problem, 2) the response of the Federal Highway Administration (FHWA) to the 

problem, and 3) highway noise barriers constructed or planned. Before discussing these items, 

however, a general discussion of the Federal-aid highway program is included to assist the 

reader. 

The Highway System

Most (97 percent) roads and streets in the United States are under the jurisdiction of State and 

local governments. The Federal jurisdiction is mainly limited to National Parks, National 

Forests, and other government-owned land. Generally in these areas, there are no permanent 

residents, yet they experience frequent human use. Noise analyses for lands under Federal 

jurisdiction should be performed on a case-by-case basis. 

Ownership of the roads in the United States is shown in Table 1. 

Table 1 

Road Ownership in the United States – 2004 

Owner Linear Miles * Percent Of All Roads

Federal 121 3 

State 775 19 

Local 3,086 78 

* Rounded to the nearest thousand 
2 

The Federal-aid highway program is a federally assisted, State administered grant program 

which provides Federal funds to State and local governments to construct and improve 

highways. The Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) set the 

course for future roles of federal, state, and local government in maintaining the country's 

highways, bridges, and mass transit facilities, and in strengthening highway safety programs. 

The ISTEA called for linking "...all forms of transportation in a unified, interconnected 

manner...economically efficient and environmentally sound...[to] move people and goods in an 

energy efficient manner." The ISTEA restructured the Federal-aid highway program and 

established two Federal-aid systems - the National Highway System (NHS) and the Interstate 

System, which is a component of the NHS. The revised Federal-aid program includes about 1.0 

million miles of the 4.0 million miles of roads in the United States. As can be seen in Table 2, 

urban roadways currently comprise a small portion of total roadways, yet carry a large portion of 

all highway travel. 

Table 2 

Classification of Roads by Functional System – 2004 

 Percent Percent of Vehicle 

System Linear Miles * of All Roads Miles Traveled

Urban 981 24.6 63.9 

Rural 3,000 75.4 36.1

TOTAL 3,981 100.0 100.0 

* Rounded to nearest thousand 

The Federal/State Relationship

 

The FHWA is the designated Federal government agency for administering the Federal-aid 

highway program. The FHWA mission is to aid States in providing safe and efficient surface 

transportation for the movement of people and goods by all modes. The FHWA is responsible 

for providing guidance to State highway agencies and metropolitan planning agencies (MPOs) 

and for reimbursing the States and MPOs for the Federal share of projects. The States, in 

cooperation with MPOs, initiate, plan, design, construct, operate, and maintain the highways on 

the Federal-aid systems. 

Federal Participation in the Cost of Projects

With a few exceptions, the FHWA does not pay for the entire cost of the projects it funds. 

Federal funds are normally "matched" with State and/or local government funds to account for 

the necessary dollars to complete the project. The Federal share is specified in legislation. 

Interstate System projects are typically funded 90 percent Federal and 10 percent State, but most 

other types of projects are funded at a slightly lower Federal share (80 percent). 
THREE-PART APPROACH TO 

NOISE ABATEMENT

Effective control of the undesirable effects of highway traffic noise requires that land use near 

highways be controlled, that vehicles themselves be quieted, and that mitigation of noise be 

undertaken on individual highway projects. 

The first component is traditionally an area of local responsibility. The other components are the 

joint responsibility of private industry and of Federal, State, and local governments. 

Land Use Planning and Control

The Federal Government has essentially no authority to regulate land use planning or the land 

development process. The FHWA and other Federal agencies encourage State and local 

governments to practice land use planning and control in the vicinity of highways. The Federal 

Government advocates that local governments use their power to regulate land development in 

such a way that noise-sensitive land uses are either prohibited from being located adjacent to a 

highway, or that the developments are planned, designed, and constructed in such a way that 

noise impacts are minimized. 

Some State and local governments have enacted legislative statutes for land use planning and 

control. As an example, the City of San Antonio’s subdivision plats’ state “For residential 

development directly adjacent to State right of way, the Developer shall be responsible for 

adequate set-back and/or sound abatement measures for future noise mitigation.” The City of 

Gilbert, Arizona places on their plat a note stating “This property could experience noise from 

the freeway.” 

Although other States and local governments have similar laws, the entire issue of land use is 

extremely complicated with a vast array of competing considerations entering into any actual 

land use control decisions. For this reason, it is nearly impossible to measure the progress of 

using land use to control the effects of noise. 

Source Control

The Noise Control Act of 1972 gives the Federal Environmental Protection Agency (EPA) the 

authority to establish noise regulations to control major sources of noise, including transportation 

vehicles and construction equipment. In addition, this legislation requires EPA to issue noise 

emission standards for motor vehicles used in Interstate commerce (vehicles used to transport 

commodities across State boundaries) and requires the Federal Motor Carrier Safety 

Administration (FMCSA) to enforce these noise emission standards. 

3 
4 

The EPA has established regulations which set emission level standards for newly manufactured 

medium and heavy trucks that have a gross vehicle weight rating (GVWR) of more than 10,000 

pounds and are capable of operating on a highway or street. Table 3 shows the maximum noise 

emission levels allowed by the EPA noise regulations for these vehicles. 

 

Table 3 

Maximum Noise Emission Levels 

as Required by EPA for Newly Manufactured Trucks 

with GVWR Over 10,000 pounds 

Effective Date Maximum Noise Level 50 feet 

 from Centerline of Travel* 

January 1, 1988 80 dBA 

* Using the Society of Automotive Engineers, Inc. (SAE), test procedure for acceleration 

under 35 mph 

For existing (in-use) medium and heavy trucks with a GVWR of more than 10,000 pounds, the 

Federal government has authority to regulate the noise emission levels only for those that are 

engaged in interstate commerce. Regulation of all other in-use vehicles must be done by State or 

local governments. The EPA emission level standards for in-use medium and heavy trucks 

engaged in interstate commerce are shown in Table 4 and are enforced by the FMCSA. 

Table 4 

Maximum Noise Emission Levels 

 as Required by EPA for In-Use Medium and Heavy Trucks 

with GVWR Over 10,000 pounds Engaged in Interstate Commerce

Effective Date Speed Maximum Noise Level 50 feet 

from Centerline of Travel 

January 8, 1986 < 35 mph 83 dBA 

January 8, 1986 > 35 mph 87 dBA 

January 8, 1986 Stationary 85 dBA 
5 

Highway Project Noise Mitigation

The National Environmental Policy Act (NEPA) of 1969 provides broad authority and 

responsibility for evaluating and mitigating adverse environmental effects including highway 

traffic noise. The NEPA directs the Federal government to use all practical means and measures 

to promote the general welfare and foster a healthy environment. 

A more important Federal legislation which specifically involves abatement of highway traffic 

noise is the Federal-Aid Highway Act of 1970. This law mandates FHWA to develop noise 

standards for mitigating highway traffic noise. 

The law requires promulgation of traffic noise-level criteria for various land use activities. The 

law further provides that FHWA not approve the plans and specifications for a federally aided 

highway project unless the project includes adequate noise abatement measures to comply with 

the standards. The FHWA has developed and implemented regulations for the mitigation of 

highway traffic noise in federally-aided highway projects. 

 

The FHWA regulations for mitigation of highway traffic noise in the planning and design of 

federally aided highways are contained in Title 23 of the United States Code of Federal 

Regulations Part 772 (attached). The regulations require the following during the planning and 

design of a highway project: 1) identification of traffic noise impacts; examination of potential 

mitigation measures; 2) the incorporation of reasonable and feasible noise mitigation measures 

into the highway project; and 3) coordination with local officials to provide helpful information 

on compatible land use planning and control. The regulations contain noise abatement criteria 

which represent the upper limit of acceptable highway traffic noise for different types of land 

uses and human activities. The regulations do not require that the abatement criteria be met in 

every instance. Rather, they require that every reasonable and feasible effort be made to provide 

noise mitigation when the criteria are approached or exceeded. Compliance with the noise 

regulations is a prerequisite for the granting of Federal-aid highway funds for construction or 

reconstruction of a highway. 
FHWA NOISE ABATEMENT 

PROCEDURES

The FHWA noise abatement procedures are codified in the Code of Federal Regulations (23 

CFR 772). The procedures are described in the following sections. 

Noise Descriptors

Noise descriptors are used to describe the time-varying nature of noise. The L10 and Leq noise 

descriptors are used in the abatement procedures. The former is the noise level exceeded 10% of 

the time in the noisiest hour of the day. The latter is the constant, average sound level, which 

over a period of time contains the same amount of sound energy as the varying levels of the 

traffic noise. The L10 is a statistical descriptor that is easy for most people to determine and 

understand. While the Leq descriptor is harder for inexperienced people to understand, it has the 

advantages over L10 of being more reliable for low-volume roadways and of permitting noise 

levels from different sources to be added directly to one another for inclusion in noise analyses. 

Leq for typical traffic conditions is usually about 3 dBA less than L10 for the same conditions. 

Impact Criteria

A traffic noise impact occurs when either of the following conditions exist: 

(1) The projected traffic noise levels approach or exceed the noise abatement criteria (NAC) 

shown in Table 9, or 

(2) The projected traffic noise levels substantially exceed the existing noise levels in an area. 

6 
7 

There is no mandated definition for what constitutes a substantial increase over existing noise 

levels in an area. Most State highway agencies use either a 10 dBA increase or a 15 dBA 

increase in noise levels to define a "substantial increase" in existing noise levels. Several State 

highway agencies use a sliding scale to define substantial increase. The sliding scale combines 

the increase in noise levels with the absolute values of the noise levels, allowing for a greater 

increase at lower absolute levels before a substantial increase occurs. 

Existing Activities

The location of existing activities in the vicinity of various study alternatives for a highway 

project are identified by individual land uses, or by broad categories of land use for which a 

single NAC level may apply. In some cases, lands which are undeveloped at the time of the 

project may be known to be under consideration for development in the future. If this is the case 

and definite commitments have been made to develop the land, then, these lands are treated as 

developed and the highway noise impacts assessed accordingly. Primary consideration for 

highway traffic noise analysis is normally given to exterior areas where frequent human use 

occurs. 

Type I/ Type II Projects

The FHWA 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. For Type I projects, 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 projects are, however, completely voluntary on 

the part of the individual States, and such projects compete for funds with all the other 

construction needs of the States. It should be noted that the National Highway System 

Designation Act of 1995 (NHS) restricted Federal participation in Type II noise barriers to those 

projects that were approved before November 28, 1995 or are proposed along lands where land 

development or substantial construction predated the existence of any highway. 

Noise Analysis

Analysis of the traffic noise impacts expected from construction of a highway involves a number 

of technical steps. The traffic noise analysis includes the following for each alternative under 

detailed study: 

 (1) identification of existing activities, developed lands, and undeveloped lands for which 

development is planned, designed and programmed, which may be affected by traffic noise 

from the highway; 

 (2) determination of existing noise levels; 

 (3) prediction of traffic noise levels; 
8 

 (4) determination of traffic noise impacts; and 

 (5) examination and evaluation of alternative noise abatement measures for reducing or 

eliminating the traffic noise impacts. 

If potential traffic noise impacts are identified, noise abatement is considered and implemented, 

if it is found to be both reasonable and feasible. The views of the impacted residents are a major 

consideration in reaching a decision on the reasonableness of abatement measures to be 

provided. When noise abatement measures are being considered, every reasonable effort is made 

to obtain substantial noise reductions. Substantial noise reductions have been defined by State 

highway agencies to typically range from 5 to 10 dBA. 

Federal Participation

Federal funds may be used for noise abatement measures where: 

 (1) a traffic noise impact has been identified, 

 (2) the noise abatement measures will reduce the traffic noise impact, and 

 (3) the overall noise abatement benefits are determined to outweigh the overall adverse social, 

economic, and environmental effects and the costs of the noise abatement measures. 

The Federal share of the abatement costs is at the same participating ratio as for the system on 

which the project is located. 

Noise Abatement

If traffic noise impacts are identified, various noise abatement measures are considered to 

mitigate the adverse impacts. The construction of a noise barrier is the mitigation measure most 

often associated with the concept of noise abatement. For this reason a special section on noise 

barriers, which begins on page 11, has been included in this report to discuss this subject in more 

detail. 

Other possible noise abatement measures include traffic management measures, creating buffer 

zones, planting vegetation, installing noise insulation in buildings, and relocating the highway. 

Traffic management measures can sometimes reduce noise problems. For example, if acceptable 

alternative truck routes are available, trucks can be prohibited from certain streets and roads, or 

they can be permitted to use certain streets and roads only during daylight hours. Traffic lights 

can be changed to smooth out the flow of traffic and to eliminate the need for frequent stops and 

starts. Speed limits can be reduced; however, about a 20 mile-per-hour reduction in speed is 

necessary for a readily noticeable (5 dBA) decrease in noise levels. 
9 

Buffer zones are undeveloped, open spaces which border a highway. Buffer zones are created 

when a highway agency purchases land, or development rights, in addition to the normal 

right-of-way, so that future dwellings cannot be constructed close to the highway. This prevents 

the possibility of constructing dwellings which would otherwise experience an excessive noise 

level from nearby highway traffic. An additional benefit of buffer zones is improvement of the 

roadside appearance. However, because of the tremendous amount of land which must be 

purchased and because in many cases dwellings already border existing roads, creating buffer 

zones is often not possible. While Federal-aid highway funds may be used on a highway project 

to create buffer zones, this measure has not been used very often. 

Vegetation, which is so high, wide, and dense that it cannot be seen over or through, can 

decrease highway traffic noise. However, it requires a 200-foot width of such vegetation to 

reduce noise by 10 decibels, which cuts in half the loudness of traffic noise. It is not feasible to 

plant enough vegetation along a road to achieve such reductions. If vegetation already exists, it 

can be saved to maintain a psychological relief, if not an actual lessening of traffic noise levels. 

If vegetation does not exist, it can be planted for psychological relief, not to reduce traffic noise 

levels. 

Insulating buildings can greatly reduce highway traffic noise, especially when windows are 

sealed and cracks and other openings are filled. Sometimes noise-absorbing material can be 

placed in the walls of new buildings during construction. However, insulation can be costly, 

because air conditioning is usually necessary once the windows are sealed. Federal-aid highway 

funds may be used for noise insulation of public-use or non-profit institutional structures. Such 

funds may also be used for noise insulation of residences and other private-use buildings where 

noise impacts are severe and no other type of abatement is possible. Very few private-use 

buildings have been noise insulated with Federal-aid highway funds. The majority of 

Federal-aid highway funds used for noise insulation has been spent to noise insulate schools. In 

many parts of the country, highway agencies do not have the authority to insulate buildings; 

thus, in those States, noise insulation cannot be included as part of a highway project. 

A noise attenuation measure which should always be considered is the possibility of altering the 

highway location to avoid those land use areas which have been determined to have a potential 

traffic noise impact. Since sound intensity decays with distance from the source, increased 

distance between the noise source and receiver will reduce the noise impact. It may also be 

possible to obtain attenuation by depressing the roadway slightly to produce a break in the line 

of sight from the source to the receiver. Potential noise reduction should be considered with the 

many other factors which influence the selection of roadway alignment. 
10 

Coordination With Local Officials

The FHWA noise regulation requires coordination with local officials whose jurisdictions are 

affected. The primary purpose of this coordination is to promote compatibility between land 

development and highways. 

Highway agencies furnish the following information to appropriate local officials: 

(1) Estimated future traffic noise levels at various distances from the highway improvement. 

(2) Locations where local communities should protect future land development from 

becoming incompatible with anticipated highway traffic noise levels. 

Traffic Noise Prediction

The FHWA Traffic Noise Model (FHWA TNM®), or any other model determined by the 

FHWA to be consistent with the methodology of the FHWA TNM must be used to analyze noise 

impacts on al Federal-aid highway projects. The FHWA also developed national averages of 

vehicle emission levels to be used in the FHWA TNM. A State Department of Transportation 

(DOT) must use these national average levels unless State-specific levels are measured based 

upon FHWA measurement procedures. For the FHWA to approve State-specific vehicle 

emission levels, a State DOT must also prove that they are different than the national average 

emission levels. 

Additional information regarding the FHWA TNM can be found at www.trafficnoisemodel.org. 

Construction Noise

Highway construction noise is often viewed by the public as being short term and a 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. If potential construction noise 

impacts are identified, a common sense approach should be utilized to incorporate appropriate 

abatement measures into the highway project. 

To aid in the analysis and determination of construction noise impacts, the FHWA has developed 

the FHWA Roadway Construction Noise Model (FHWA RCNM). This model is not required to 

be used on Federal-aid projects; however, this model is a screening tool that can be used for the 

prediction of construction noise during the project development and construction phases. 

Additional information regarding the FHWA RCNM can be found at www.rcnm.us. 
NOISE BARRIERS 

CONSTRUCTED OR PLANNED 

Noise barriers are solid obstructions built between the highway and the homes along the 

highway. Effective noise barriers can reduce noise levels by ten to fifteen decibels, cutting the 

loudness of traffic noise in half. Barriers can be formed from earth mounds along the road 

(usually called earth berms) or from high, vertical walls. Earth berms have a very natural 

appearance and are usually attractive. However, an earth berm can require quite a lot of land, if 

it is very high. Walls take less space. They are usually limited to eight meters in height because 

of structural and aesthetic reasons. Noise walls can be built out of wood, stucco, concrete, 

masonry, metal, and other materials. Noise barriers are designed and constructed to be visually 

pleasing and blend with their surroundings. 

Noise Barriers Constructed

The Federal-aid highway program has always been based on a strong State-Federal partnership. 

At the core of that partnership is a philosophy of trust and flexibility, and a belief that the States 

are in the best position to make investment decisions that are based on the needs and priorities of 

their citizens. The FHWA noise regulations give each State department of transportation (DOT) 

flexibility in determining the reasonableness and feasibility of noise abatement and, thus, in 

balancing the benefits of noise abatement against the overall adverse social, economic, and 

environmental effects and costs of the noise abatement measures. The State DOT must base its 

determination on the interest of the overall public good, keeping in mind all the elements of the 

highway program (need, funding, environmental impacts, public involvement, etc.). Congress 

affirmed and extended the philosophy of partnership, trust, and flexibility in the enactment of 

ISTEA. 

The flexibility in noise abatement decision-making is reflected by data indicating that some 

States have built many noise barriers and some have built none. Through the end of 2004, 

forty-five State DOTs and the Commonwealth of Puerto Rico have constructed over 2,205 linear 

miles of barriers at a cost of over $2.7 billion ($3.4 billion in 2004 dollars). Five States and the 

District of Columbia have not constructed noise barriers to date. Table 6 lists the ten States that 

have constructed the most noise barriers, in terms of area, length, and cost. The cost data in 

Table 5 give a general indication of trends. However, the data should not be used for exact 

comparisons, since precise, uniform individual barrier costs are very difficult to obtain. Table 6 

shows total noise barrier areas by material type. Table 7 lists the five States that have not 

constructed noise barriers to date. 

11 
12 

Note: California has not supplied 1998-2004 barrier data.

Table 5 

Noise Barrier Construction By State 

Through 2004

 Square Feet Linear

 (Thousands) Miles

 California 30,644 California 482.8 

 Virginia 11,227 Arizona 155.1 

 Arizona 11,226 Virginia 127.5 

 New Jersey 9,440 Ohio 112.4 

 Ohio 8,675 New Jersey 96.9 

 Maryland 8,422 Colorado 92.5 

 Minnesota 7,187 New York 90.7 

 New York 7,011 Pennsylvania 87.0 

 Florida 6,700 Minnesota 83.7 

 Pennsylvania 6,415 Maryland 81.8 

 _____ ______ 

 10 State Total 106,946 1,410.4

 Actual Cost 2004 Dollars

 (Millions) (Millions) 

 California $399.6 California $592.8 

 Arizona 258.7 Arizona 284.6 

 New Jersey 202.4 New Jersey 277.5 

 Maryland 200.9 Maryland 253.6 

 Virginia 169.6 Virginia 225.3 

 

 New York 165.9 New York 207.3 

 Pennsylvania 159.6 Pennsylvania 197.8 

 Florida 150.7 Florida 175.9 

 Ohio 117.2 Ohio 139.0 

 Colorado 80.0 Minnesota 107.7 

 ______ _______ 

 10 State Total $1,904.5 $2,461.4
13 

Table 6

Total Noise Barrier Area by Material Type

 Through 2004

Single Material Barriers Combination Barriers

 Square Feet Square Feet

Material (Thousands) Material (Thousands) 

Concrete/Precast 67,926 Wood /Concrete 4,281 

Block 33,993 Berm/Wood 2,990 

Concrete/Unspecified 13,715 Concrete/Block 2,154 

Wood/Post & Plank 5,912 Other 1,930 

Metal/Unspecified 4,279 Berm/Concrete 1,863 

Berm Only 4,281 Metal/Concrete 1,786 

Wood/Glue Laminated 3,701 Berm/Metal 1,439 

Absorptive 3,629 Berm/Block 795 

Wood/Unspecified 3,055 Concrete/Brick 586 

Other 1,812 Wood/Metal 464 

Brick 1,152 Berm/Wood/Concrete 348 

 Wood/Block 283 

 Berm/Wood/Metal 171 

 Block/Brick 8 

 ______ _____ 

Total 143,455 Total 19,098 

Table 7 

States That Have Not Constructed Noise Barriers to Date

 Alabama Mississippi Montana Rhode Island South Dakota 
14 

Effectiveness

 

Noise barriers can be quite effective in reducing noise for receptors 

within approximately 200 feet of a highway. Table 8 summarizes barrier attenuation. 

Table 8 

Barrier Attenuation 

Reduction in Reduction in Degree of Difficulty 

Sound Level Acoustic Energy To Obtain Reduction 

 5 dBA 70% Simple 

 10 dBA 90% Attainable 

 15 dBA 97% Very Difficult 

 20 dBA 99% Nearly Impossible 

Barriers do have limitations. For a noise barrier to work, it must be high enough and long 

enough to block the view of a road. Noise barriers do very little good for homes on a hillside 

overlooking a road or for buildings, which rise above the barrier. Openings in noise walls for 

driveway connections or intersecting streets greatly reduce the effectiveness of barriers. In some 

areas, homes are scattered too far apart to permit noise barriers to be built at a reasonable cost. 

Public Perception

Overall, public reaction to highway noise barriers appears to be positive. There is, however, a 

wide diversity of specific reactions to barriers. Residents adjacent to barriers have stated that 

conversations in households are easier, sleeping conditions are better, a more relaxing 

environment is created, windows are opened more often, and yards are used more in the summer. 

Perceived non-noise benefits include increased privacy, cleaner air, improved view and sense of 

ruralness, and healthier lawns and shrubs. Negative reactions have included a restriction of 

view, a feeling of confinement, a loss of air circulation, a loss of sunlight and lighting, and poor 

maintenance of the barrier. Most residents near a barrier seem to feel that barriers effectively 

reduce traffic noise and that the benefits of barriers outweigh the disadvantages of the barriers. 

Research Efforts

Over the last two decades, much work has been done within the highway program to develop the 

basic tools necessary to analyze the impacts of highway traffic noise. Efforts have focused on 

the establishment of criteria for considering highway traffic noise, the measurement and 

prediction of noise levels, and the development and evaluation of feasible measures to abate 

highway traffic noise. Today, research efforts are continuing to assure that analysis tools reflect 

the current state-of-the-art in highway traffic noise, while meeting the program needs of State 

highway agencies. 
Highway traffic noise research has been guided and continues to be guided by representatives of 

State DOTs, other State government agencies, local government agencies, Federal agencies, and 

the academic and private sectors. An important part of this cooperative effort is the work of the 

Transportation Research Board Committee on Transportation-Related Noise and Vibration, 

which has been instrumental in identifying and prioritizing research needs. Another important 

part of this effort is the research work that individual States conduct within their own highway 

programs. 

Future research efforts will strive to produce more cost effective solutions and efficient 

allocation of resources to deal with the problems of highway traffic noise. Emphasis is 

anticipated in the areas of traffic noise prediction and abatement analysis. 

SUMMARY 

The United States has undertaken a program which utilizes a three-part approach to the 

abatement of highway traffic noise. Noise-compatible development through effective land use 

planning and control is traditionally an area of local responsibility. Source control or control of 

noise emissions from the vehicles themselves is a joint responsibility of private industry and of 

Federal, State, and local governments. The FHWA has established noise standards for different 

types of land use activities adjacent to highways. These standards require that for certain types 

of federally-aided highway projects, States must conduct noise analyses to identify potential 

highway traffic noise impacts. If impacts are identified, noise abatement measures must be 

considered and implemented, if determined to be both reasonable and feasible. Among the 

various types of possible abatement measures, the construction of noise barriers is most 

commonly used. 

15 
APPENDIX

23 CFR PART 772 - PROCEDURES FOR ABATEMENT OF 

HIGHWAY TRAFFIC NOISE AND CONSTRUCTION NOISE 

Sec. 

772.1 Purpose. 

772.3 Noise Standards. 

772.5 Definitions. 

772.7 Applicability. 

772.9 Analysis of Traffic Noise Impacts and Abatement Measures. 

772.11 Noise Abatement. 

772.13 Federal Participation. 

772.15 Information for Local Officials. 

772.17 Traffic Noise Prediction. 

772.19 Construction Noise. 

Table 1 - Noise Abatement Criteria 

Appendix A - National Reference Energy Mean Emission Levels as a Function of Speed

AUTHORITY: 23 U.S.C. 109(h), 109(i); 42 U.S.C. 4331, 4332; sec. 339(b), Pub. L. 104-59, 

109 Stat. 568, 605; 49 CFR 1.48(b). 

(Source: 47 FR 29654, July 8, 1982; 47 FR 33956, Aug. 5, 1982, 

and 62 FR 42903, August 11, 1997) 

Sec. 772.1 Purpose. 

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.). 

Sec. 772.3 Noise Standards. 

The highway traffic noise prediction requirements, noise analyses, noise abatement 

criteria, and requirements for informing local officials in this regulation constitute the noise 

standards mandated by 23 U.S.C. 109(i). All highway projects which are developed in 

conformance with this regulation shall be deemed to be in conformance with the Federal 

Highway Administration (FHWA) noise standards. 

Sec. 772.5 Definitions. 

(a) Design year. The future year used to estimate the probable traffic volume for which a 

highway is designed. A time, 10 to 20 years, from the start of construction is usually used. 

 

(b) Existing noise levels. The noise, resulting from the natural and mechanical sources and 

human activity, considered to be usually present in a particular area. 

 

(c) L10. The sound level that is exceeded 10 percent of the time (the 90th percentile) for the 

period under consideration. 

(d) L10(h). The hourly value of L10. 

16 
17 

 

(e) Leq. The equivalent steady-state sound level which in a stated period of time contains 

the same acoustic energy as the time-varying sound level during the same time period. 

(f) Leq(h). The hourly value of Leq. 

(g) Traffic noise impacts. Impacts which occur when the predicted traffic noise levels 

approach or exceed the noise abatement criteria (Table 1), or when the predicted traffic noise 

levels substantially exceed the existing noise levels. 

 

(h) Type I projects. 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 

which significantly changes either the horizontal or vertical alignment or increases the number of 

through-traffic lanes. 

 

(i) Type II projects. A proposed Federal or Federal-aid highway project for noise 

abatement on an existing highway. 

Sec. 772.7 Applicability.

 

(a) Type I projects. This regulation applies to all Type I projects unless it is specifically 

indicated that a section applies only to Type II projects. 

 

(b) Type II projects. The development and implementation of Type II projects are not 

mandatory requirements of 23 U.S.C. 109(i) and are, therefore, not required by this regulation. 

When Type II projects are proposed for Federal-aid highway participation at the option of the 

highway agency, the provisions of Subsec. 772.9(c), 772.13, and 772.19 of this regulation 

shall apply. 

Sec. 772.9 Analysis of Traffic Noise Impacts and Abatement Measures. 

 

(a) The highway agency shall determine and analyze expected traffic noise impacts and 

alternative noise abatement measures to mitigate these impacts, giving weight to the benefits and 

cost of abatement, and to the overall social, economic and environmental effects. 

 

(b) The traffic noise analysis shall include the following for each alternative under detailed 

study: 

 

(1) Identification of existing activities, developed lands, and undeveloped lands for 

which development is planned, designed and programmed, which may be affected 

by noise from the highway; 

 

(2) Prediction of traffic noise levels; 

 

(3) Determination of existing noise levels; 

 

(4) Determination of traffic noise impacts; and 

 

(5) Examination and evaluation of alternative noise abatement measures for 

reducing or eliminating the noise impacts. 

 

(c) Highway agencies proposing to use Federal-aid highway funds for Type II projects 

shall perform a noise analysis of sufficient scope to provide information needed to make the 

determination required by Sec. 772.13(a) of this chapter. 
18 

Sec. 772.11 Noise Abatement. 

 

(a) In determining and abating traffic noise impacts, primary consideration is to be given 

to exterior areas. Abatement will usually be necessary only where frequent human use occurs 

and a lowered noise level would be of benefit. 

 

(b) In those situations where there are no exterior activities to be affected by the traffic 

noise, or where the exterior activities are far from or physically shielded from the roadway in a 

manner that prevents an impact on exterior activities, the interior criterion shall be used as the 

basis of determining noise impacts. 

 

(c) If a noise impact is identified, the abatement measures listed in Sec. 772.13(c) of this 

chapter must be considered. 

 

(d) When noise abatement measures are being considered, every reasonable effort shall be 

made to obtain substantial noise reductions. 

 

(e) Before adoption of a final environmental impact statement or finding of no significant 

impact, the highway agency shall identify: 

 

(1) Noise abatement measures which are reasonable and feasible and which are 

likely to be incorporated in the project, and 

 

(2) Noise impacts for which no apparent solution is available. 

 

(f) The views of the impacted residents will be a major consideration in reaching a 

decision on the reasonableness of abatement measures to be provided. 

 

(g) The plans and specifications will not be approved by FHWA unless those noise 

abatement measures which are reasonable and feasible are incorporated into the plans and 

specifications to reduce or eliminate the noise impact on existing activities, developed lands, or 

undeveloped lands for which development is planned, designed, and programmed. 

Sec. 772.13 Federal Participation. 

 

(a) Federal funds may be used for noise abatement measures where: 

 

(1) A traffic noise impact has been identified, 

 

(2) The noise abatement measures will reduce the traffic noise impact, and 

 

(3) The overall noise abatement benefits are determined to outweigh the overall 

adverse social, economic, and environmental effects and the costs of the noise 

abatement measures. 

 

 (b) For Type II projects, noise abatement measures will only be approved for projects that 

were approved before November 28, 1995, or are proposed along lands where land development 

or substantial construction predated the existence of any highway. The granting of a building 

permit, filing of a plat plan, or a similar action must have occurred prior to right-of-way 

acquisition or construction approval for the original highway. Noise abatement measures will 

not be approved at locations where such measures were previously determined not to be 

reasonable and feasible for a Type I project. 

 

(c) The noise abatement measures listed below may be incorporated in Type I and Type II 

projects to reduce traffic noise impacts. The costs of such measures may be included in 
19 

Federal-aid participating project costs with the Federal share being the same as that for the 

system on which the project is located, except that Interstate construction funds may only 

participate in Type I projects. 

 

(1) Traffic management measures (e.g., traffic control devices and signing for 

prohibition of certain vehicle types, time-use restrictions for certain vehicle types, 

modified speed limits, and exclusive lane designations). 

 

(2) Alteration of horizontal and vertical alignments. 

 

(3) Acquisition of property rights (either in fee or lesser interest) for construction of 

noise barriers. 

 

(4) Construction of noise barriers (including landscaping for aesthetic purposes) 

whether within or outside the highway right-of-way. Interstate construction funds 

may not participate in landscaping. 

 

(5) Acquisition of real property or interests therein (predominantly unimproved 

property) to serve as a buffer zone to preempt development which would be 

adversely impacted by traffic noise. This measure may be included in Type I 

projects only. 

 

(6) Noise insulation of public use or nonprofit institutional structures. 

 

(d) There may be situations where (1) severe traffic noise impacts exist or are expected, 

and (2) the abatement measures listed above are physically infeasible or economically 

unreasonable. In these instances, noise abatement measures other than those listed in Sec. 

772.13(c) of this chapter may be proposed for Types I and II projects by the highway agency and 

approved by the FHWA on a case-by-case basis when the conditions of Sec. 772.13(a) of this 

chapter have been met. 

Sec. 772.15 Information for Local Officials. 

 

In an effort to prevent future traffic noise impacts on currently undeveloped lands, 

highway agencies shall inform local officials within whose jurisdiction the highway project is 

located of the following: 

 

(a) The best estimation of future noise levels (for various distances from the highway 

improvement) for both developed and undeveloped lands or properties in the immediate 

vicinity of the project, 

 

(b) Information that may be useful to local communities to protect future land 

development from becoming incompatible with anticipated highway noise levels, and 

 

(c) Eligibility for Federal-aid participation for Type II projects as described in Sec. 

772.13(b) of this chapter. 

§ 772.17 Traffic noise prediction. 

(a) Any analysis required by this subpart must use the FHWA Traffic Noise Model 

(FHWA TNM), which is described in “FHWA Traffic Noise Model” Report No. FHWA–

PD–96–010, including Revision No. 1, dated April 14, 2004, or any other model 

determined by the FHWA to be consistent with the methodology of the FHWA TNM. 

These publications are incorporated by reference in accordance with 5 U.S.C. 552(a) and 1 
20 

CFR part 51 and are on file at the National Archives and Record Administration (NARA). 

For information on the availability of this material at NARA call (202) 741–6030, or go to 

http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html. 

These documents are available for copying and inspection at the Federal Highway 

Administration, 400 Seventh Street, SW., Room 3240, Washington, DC 20590, as 

provided in 49 CFR part 7. These documents are also available on the FHWA's Traffic 

Noise Model Web site at the following URL: http://www.trafficnoisemodel.org/main.html. 

(b) In predicting noise levels and assessing noise impacts, traffic characteristics which will 

yield the worst hourly traffic noise impact on a regular basis for the design year shall be 

used. 

Sec. 772.19 Construction Noise. 

 

The following general steps are to be performed for all Types I and II projects: 

 

(a) Identify land uses or activities which may be affected by noise from construction of the 

project. The identification is to be performed during the project development studies. 

 

(b) Determine the measures which are needed in the plans and specifications to minimize 

or eliminate adverse construction noise impacts to the community. This determination 

shall include a weighing of the benefits achieved and the overall adverse social, economic 

and environmental effects and the costs of the abatement measures. 

 

(c) Incorporate the needed abatement measures in the plans and specifications. 
21 

TABLE 9

Noise Abatement Criteria (NAC) 

Hourly A-Weighted Sound Level - decibels (dBA)* 

Activity 

Category Leq(h) L10(h) Description of Activity Category

 A 57 60 Lands on which serenity and quiet are of 

 (Exterior) (Exterior) extraordinary significance and serve an important public need and 

where the preservation of those qualities is essential if the area is to 

continue to serve its intended purpose. 

 B 67 70 Picnic areas, recreation areas, playgrounds, 

 (Exterior) (Exterior) active sports areas, parks, residences, motels, hotels, schools, 

churches, libraries, and hospitals. 

 C 72 75 Developed lands, properties, or activities not 

 (Exterior) (Exterior) included in Categories A or B above. 

 D -- -- Undeveloped lands. 

 E 52 55 Residences, motels, hotels, public meeting rooms, 

 (Interior) (Interior) schools, churches, libraries, hospitals, and auditoriums. 

* Either L10(h) or Leq(h) (but not both) may be used on a project