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Highway Traffic Noise Analysis and Abatement Policy and Guidance

FHWA Noise Regulations

The current FHWA procedures for highway traffic noise analysis and abatement are contained in 23 CFR 772, "Procedures for Abatement of Highway Traffic Noise and Construction Noise." These procedures specify the requirements that SHAs must meet when using Federal-aid funds for highway projects.

This discussion will address those requirements and point out the most important issues related to the requirements. Each paragraph of 23 CFR 772 will be presented in boldface type and followed by a discussion of that paragraph. Some parts are self-explanatory and need only a sentence or two of discussion. Other, more complicated paragraphs will have greater discussion.

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.).

The protection of the public's health and welfare is an important responsibility that FHWA helps to accomplish during the planning and design of a highway project. The U.S. Congress has directed that this be done when the 1970 Federal-Aid Highway Act was passed. Concerned citizens and States encouraged Congress to provide this protection.

772.3: NOISE STANDARDS. The highway traffic noise prediction requirements, noise analyses, noise abatement criteria, and requirements for informing local officials in this directive constitute the noise standards mandated by 23 U.S.C. 109(i). All highway projects which are developed in conformance with this directive shall be deemed to be in conformance with the Federal Highway Administration (FHWA) noise standards.

This paragraph makes the whole 23 CFR 772 the FHWA noise standard. The standard is required by 23 U.S.C. 109(i). Some people mistake the noise abatement criteria for the FHWA standard. Early on, FHWA did not want to be restricted to specific noise levels that may not be achieved in most highway projects. So, a standard was developed that would best serve the public in terms of protection and reasonable cost.


  1. 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.
  2. Existing Noise Levels - the noise, resulting from the natural and mechanical sources and human activity, considered to be usually present in a particular area.
  3. L10 - the sound level that is exceeded 10 percent of the time (the 90th percentile) for the period under consideration.
  4. L10(h) - the hourly value of L10.
  5. Leq - the equivalent steady-state sound level which in a stated period of time contains the same acoustic energy as a time-varying sound level during the same period.
  6. Leq(h) - the hourly value of Leq.
  7. Traffic Noise Impacts - impacts which occur when the predicted traffic noise levels approach or exceed the noise abatement criteria (Table 5), or when the predicted traffic noise levels substantially exceed the existing noise levels.
  8. 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.
  9. Type II Projects - a proposed Federal or Federal-aid highway for noise abatement on an existing highway.

Most of these definitions are self-explanatory. However, the definition for "Traffic Noise Impacts" warrants further attention. A traffic noise impact occurs when the predicted levels approach or exceed the noise abatement criteria (NAC) or when predicted traffic noise levels substantially exceed the existing noise level, even though the predicted levels may not exceed the NAC. This definition reflects the FHWA position that traffic noise impacts can occur under either of two separate conditions: (1) when noise levels are unacceptably high (absolute level); or (2) when a proposed highway project will substantially increase the existing noise environment (substantial increase). In order to adequately assess the noise impact of a proposed project, both criteria must be analyzed. While the FHWA noise regulations do not define "approach or exceed, all SHAs must establish a definition of "approach" that is at least 1 dBA less than the NAC for use in identifying traffic noise impacts in traffic noise analyses.

Table 5: Noise Abatement Criteria (NAC) Hourly A-Weighted Sound Level in Decibels (dBA)*
Leq(h) L10(h) Description of Activity Category
A 57 (Exterior) 60 (Exterior) Lands on which serenity and quiet are of 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 (Exterior) 70 (Exterior) Picnic areas, recreation areas, playgrounds, active sports areas, parks, residences, motels, hotels, schools, churches, libraries, and hospitals.
C 72 (Exterior) 75 (Exterior) Developed lands, properties, or activities not included in Categories A or B above.
D -- -- Undeveloped lands.
E 52 (Interior) 55 (Interior) Residences, motels, hotels, public meeting rooms, schools, churches, libraries, hospitals, and auditoriums.

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

NOTE:These sound levels are only to be used to determine impact. These are the absolute levels where abatement must be considered. Noise abatement should be designed to achieve a substantial noise reduction - not the noise abatement criteria.

In developing the NAC contained in the noise regulations, the FHWA attempted to strike a balance between that which is most desirable and that which is feasible. Factors such as technical feasibility, the unique characteristics of highway-generated noise, cost, overall public interest, and other agency objectives were important elements in the process of setting a standard. Establishing values for the NAC was approached by attempting to balance the control of future increases in highway noise levels and the economic, physical, and aesthetic considerations related to noise abatement measures. Numerous approaches were considered in establishing the criteria, including (1) hearing impairment, (2) annoyance, sleep, and task interference or disturbance, and (3) interference with speech communication. The first deals in terms of very loud noises seldom encountered for a highway project beyond the roadway proper. The second approach was desirable in principle but was insufficiently researched to be useful in practice. However, the third approach - speech interference - was usefully applied to the problem of highway traffic noise. Thus, it should be remembered that the NAC are based upon noise levels associated with interference of speech communication and that the NAC are a compromise between noise levels that are desirable and those that are achievable. FHWA believes that our regulations provide a well-balanced approach to the problem of highway-traffic-generated noise.

The NAC are not magical numbers. Traffic noise impacts can occur below the NAC. The NAC should not be viewed as Federal standards or desirable noise levels; they should not be used as design goals for noise barrier construction. All of the regulations contained in 23 CFR 772 constitute the standards mandated by the Federal-Aid Highway Act of 1970. Noise abatement should be designed to achieve a substantial noise reduction, which SHAs have defined in practice to be in the range of 5-10 dBA. The NAC should only be used as absolute values which, when approached or exceeded, require the consideration of traffic noise abatement measures.

The 23 CFR 772 purposefully provides the SHAs with flexibility to establish their own definition of "substantial increase." A 10 dBA increase in noise levels is a doubling of the perceived loudness. A 15 dBA increase in noise levels represents more than a doubling of the loudness. Factors such as available resources, the public's attitudes toward highway traffic noise, and the absolute noise levels may influence a State's definition. The FHWA will accept a well-reasoned definition that is uniformly and consistently applied. Several SHA definitions have evolved and are shown in Table 6.

Table 6: Criteria Used by States to Define"Substantial"
  Increase (dB) Subjective Descriptor
Criteria 1 0-5
Little increase
Some increase
Substantial increase
Criteria 2 <10
Little increase
Substantial increase
Criteria 3 0-5
No increase
Minor increase
Moderate increase
Substantial increase

The use of subjective descriptors to describe traffic noise impacts is not required. Traffic noise impacts occur based upon the definition contained in 23 CFR 772. This definition does not contain subjective descriptors. If impacts are identified, noise abatement measures must be considered and implemented if found to be reasonable and feasible. When analyzing the reasonableness of abatement, SHAs should consider the relationship between the absolute noise levels and the extent of the increase over existing noise levels for a given situation. A small increase at a higher absolute level (e.g., 70 dBA to 75 dBA) can be more important and justify greater consideration than a similar increase at a lower absolute level (e.g, 50 dBA to 55 dBA). Likewise, a large increase at a lower absolute level (e.g., 40 dBA to 55 dBA) can be less important and justify less consideration than a similar increase at a higher absolute level (e.g., 55 dBA to 70 dBA).


  1. Type I Projects. This directive applies to all Type I projects unless it is specifically indicated that a section applies only to Type II projects.
  2. 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 directive. When Type II projects are proposed for Federal-aid highway participation at the option of the highway agency, the provisions of paragraphs 6, 8, and 11 of this directive shall apply.

The regulation applies to all Type I and Type II projects. The implementation of a Type II program is optional and not mandatory.


  1. 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.
  2. 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.
  3. 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 paragraph 772.13a of this directive.

Paragraph 772.9a is the major requirement for doing noise analyses on all Type I projects. However, this requirement includes the evaluation of noise reduction benefits, abatement cost, and social, economic, and environmental (SEE) effects. This evaluation requires a balancing by the SHA of benefits versus disbenefits. This can be a difficult task because very little guidance exists on this topic. Noise reduction benefits and abatement cost will be discussed in detail in paragraph 772.11. The process of balancing noise abatement and the SEE effects of the mitigation is strongly influenced by the public involvement process. The people who live next to the highway project can best evaluate if the abatement benefits will outweigh the SEE effects. The SHAs should not do this evaluation without public involvement. It is also important to remember that noise abatement consideration should be an inherent project consideration that is not handled separately but is incorporated and considered in the total project development decision.

Paragraph 772.9b lists the minimum requirements needed to adequately evaluate the impacts and abatement for each alternative under detailed study for the proposed highway project. The analysis should present the noise impacts and evaluation of alternative abatement measures in a comparative format. In this way, the potential noise impacts and likely abatement measures associated with the various alternatives, including the "no-build" alternative, are clearly defined. Detailed procedures on how to do the analysis exists in the text of the National Highway Institute noise training course, "Fundamentals and Abatement of Highway Traffic Noise." Paragraph 772.9b(1) requires the identification of existing activities and developed lands. This identification includes not only the type (e.g., residential, commercial), but the number or extent of activities. This quantification is often overlooked in the analysis. The extent of the noise impact on the people living near the highway project cannot be evaluated correctly without the quantification of the existing activities.

Paragraph 772.9b(1) also requires noise analysis for undeveloped lands for which development is "planned, designed, and programmed." The terms "... planned, designed, and programmed ..." mean that: 1) a definite commitment has been made to develop the property in question, and 2) there is also official knowledge (such as through a public agency) that such development has been "planned, designed, and programmed." A definite commitment means that a developer has shown a definite interest to develop the land within a reasonable period of time and has reached a point where he can no longer practically change his plans.

The exact date for determining when undeveloped land is "... planned, designed, and programmed ..." for development is not specified in 23 CFR 772. Each SHA and accompanying FHWA Division Office should establish a mutually acceptable specific date that is appropriate for the development process in their respective State. One specific date that has evolved is the date of issuance of a building permit. Other dates used by States include the date of final approval of the development plan and the date of recording of the plat plan. Any of these dates are in conformance with FHWA policy.


  1. 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.
  2. 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.

    In most situations, if the exterior area can be protected, the interior will also be protected. The selection of the exterior area where "frequent human use occurs" is very important. This requires a site visit to determine whether people are using the entire exterior area or only a small portion, like a patio or porch. Some States choose the right-of-way line (a point farthest away from a house) to be on the conservative side when doing the noise impact analysis. Interior use applies mostly to hospitals and schools.

    Interior noise level predictions may be computed by subtracting from the predicted exterior levels the noise reduction factors for the building in question. If field measurements of these noise reduction factors are obtained or the factors are calculated from detailed acoustical analyses, the measured or calculated reduction factors should be used. In the absence of such calculations or field measurements, the noise reduction factors may be obtained from the following table:

    Table 7: Building Noise Reduction Factors
    Noise Reduction Due to Exterior of the
    Building Type Window Condition Structure
    All Open 10 dB
    Light Frame Ordinary Sash (closed) 20 dB
      Storm Windows 25 dB
    Masonry Single Glazed 25 dB
    Masonry Double Glazed 35 dB

    NOTE:The windows shall be considered open unless there is firm knowledge that the windows are in fact kept closed almost every day of the year.

  3. If a noise impact is identified, the abatement measures listed in paragraph 772.13c of this directive must be considered.

    This self-explanatory paragraph requires consideration of noise abatement when noise impacts occur. As noted in paragraph 772.5g, noise impacts occur when noise levels approach or exceed the noise abatement criteria or when predicted levels substantially exceed existing levels. Consequently, this paragraph requires consideration of noise abatement for both of these types of noise impacts.

  4. When noise abatement measures are being considered, every reasonable effort shall be made to obtain substantial noise reductions.

    Abatement must provide at least a 5 dBA reduction in highway traffic noise levels in order to provide noticeable and effective attenuation. When noise abatement is proposed, it is recommended that an attempt be made to achieve the greatest reduction possible. SHAs have generally defined substantial reduction to be in the range of 5-10 dBA.

    This paragraph does not say to reduce to the noise abatement criteria; it says "substantial noise reductions." Consequently, a projected noise level of Leq 69 for a Category B activity (see Table 5) should not be abated merely to the noise abatement criterion of Leq 67, but rather a substantial reduction should be obtained (at least 5 dBA). The choice of what minimum reduction to strive for is certainly a subjective one and is probably related to data found in technical literature, such as the following table.

    Table 8: Relationship Between Decibel, Energy, and Loudness
    A-Level Down Remove % of Energy Divide Loudness by
    3 dBA 50 1.2
    6 dBA 75 1.5
    10 dBA 90 2
    20 dBA 99 4

    A reduction of 10 dBA (say 75 dBA to 65 dBA) will be perceived by the public as a halving of the loudness. This is an easily recognizable change. 5 dBA and 7 dBA changes can also be recognized, but to a lesser degree. Two points should be kept in mind: (1) any reduction will improve the noise environment in such areas as annoyance, speech interference, task interference, etc., and (2) no matter what the reduction, until the level reaches a very low level (about Leq = 55 dBA), the noise environment will continue to be dominated by traffic noise that is clearly audible.

  5. 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.

    This paragraph ties the noise regulation to the NEPA requirements. An important point is that the requirements for the draft environmental impact statement (EIS) are the same as the final. Therefore, the information for both 772.11e(1) and 772.11e(2) are needed in the draft EIS and the final EIS. The choice of the word "likely" was deliberate. If a decisionmaker is to make an informed decision and if the public is to be made aware of the impacts, the State must make its intentions known. If the State later decides that mitigation is not warranted, the decision should have strong support. If the State would like to qualify the word "likely," this is acceptable. When a project involves consideration of more than one barrier, a statement of "likelihood" for each barrier should be included in the environmental document. The following is an illustration of some appropriate words.

    Based on the studies so far accomplished, the State intends to install noise abatement measures in the form of a barrier at . These preliminary indications of likely abatement measures are based upon preliminary design for a barrier cost of $ that will reduce the noise level by dBA for residents. If it subsequently develops during final design that these conditions have substantially changed, the abatement measures might not be provided. A final decision of the installation of the abatement measure(s) will be made upon completion of the project design and the public involvement processes.

  6. The views of the impacted residents will be a major consideration in reaching a decision on the reasonableness of abatement measures to be provided.

    The views of the impacted residents should be a major consideration in determining the reasonableness of traffic noise abatement measures for proposed highway construction projects. The views should be determined and addressed during the environmental phase of project development. The will and desires of the general public should be an important factor in dealing with the overall problems of highway traffic noise. SHAs should incorporate traffic noise consideration in their on-going activities for public involvement in the highway program, i.e., the residents' views on the desirability and acceptability of abatement need to be reexamined periodically during project development.

  7. 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.

    This is a summary statement of the requirements in the 1970 Federal-Aid Highway Act [23 U.S.C. 109(i)].

    The key words in this paragraph are "reasonable" and "feasible." For a thorough explanation of reasonableness and feasibility of abatement, see the discussion on pp. 50-56.


  1. 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.

    Paragraph 772.13a identifies the simple rules that guide the funding of noise abatement on highway projects. These rules apply to both Type I and Type II projects.

    Federal-aid highway funds may not be used as payment or compensation for a traffic noise impact through the purchase of a noise easement from a property owner. The FHWA noise regulations clearly indicate that Federal funds may only be used to reduce traffic noise impacts and provide noise abatement benefits. Monetary compensation accomplishes neither of these requirements.

    Federal-aid funds may be used in compensation paid during right-of-way negotiations for a partial taking of property. Noise, air quality, access, visual quality, etc. are frequently considered jointly in determining this compensation, which is regarded as part of right-of-way acquisition, not environmental mitigation.

  2. For Type II projects, noise abatement measures will not normally be approved for those activities and land uses which come into existence after May 14, 1976. However, noise abatement measures may be approved for activities and land uses which come into existence after May 14, 1976, provided local authorities have taken measures to exercise land use control over the remaining undeveloped lands adjacent to highways in the local jurisdiction to prevent further development of incompatible activities.

    Paragraph 772.13b limits funding participation for retrofit barriers on existing highways because in 1976 FHWA publicly stated that local governments must help control noise impacts through noise-compatible land-use planning and zoning. However, it is important to remember that this paragraph does not prohibit the approval of Type II barriers after 1976. It says that the land use activity (housing development) built near a highway after 1976 usually cannot get a Type II barrier unless the local government has an active land use control program to prevent future incompatible activities (e.g., zoning requirements, noise-sensitive growth and development procedures, local ordinances). The FHWA has not rigidly applied this requirement in the past. However, after the date of issuance of this guidance, Type II abatement projects for new activities and land uses which come into existence may only be approved if an active local land use control program was adopted prior to existence of the new activities and land uses. EXAMPLE: A Type II noise barrier is requested for homes that were constructed prior to a local community's adoption of an active noise-compatible land use control program. Type II abatement may not be approved for this location. SHAs should be certain to make local officials aware of this requirement (see paragraph 772.15 on page 18).

  3. 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 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. signing for prohibition of certain vehicle types, time-use restrictions for certain vehicle types, modified speed limits, and exclusive land 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 (predominately 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, and
    6. noise insulation of public use or nonprofit institutional structures.

    Two important points about this paragraph are: (l) the participating share is the same as that for the system on which the project is located; (2) buffer zones can only be used in Type I projects. The potential use of buffer zones applies to predominantly unimproved property. This authority is not used to purchase homes or developed property to create a noise buffer zone. It is used to purchase unimproved property to preclude future noise impacts where development has not yet occurred.

    Although most noise mitigation has been implemented along Interstate highways, Federal funds may be used for mitigation measures along other types of highways if the noise impacts exist and the criteria in 772.13a are met.

    The most-used abatement measure is the noise barrier; however, paragraph 772.11c requires consideration of all the abatement measures listed in paragraph 772.13c. Noise insulation may only routinely be considered for public use or nonprofit institutional structures, e.g., churches, schools, hospitals, libraries, etc. Private dwellings may only be noise-insulated under the provisions of Section 772.13d.

    The purchase of a noise easement, in locations where traffic noise impacts are expected to occur or already exist, should not be considered as a noise abatement measure. It does not reduce noise levels or abate the impacts. It only provides monetary compensation and is, thus, not eligible for Federal-aid participation.

  4. 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 paragraph 771.13c of this directive may be proposed for Type I and II projects by the highway agency and approved by the Regional Federal Highway Administrator on a case-by-case basis when the conditions of paragraph 772.13a of this directive have been met.

    This paragraph allows the States the flexibility to propose innovative noise abatement measures when severe traffic noise impacts are anticipated and normal abatement measures are physically infeasible or economically unreasonable. In these instances, the Regional Federal Highway Administrator may approve a State's request for unusual or extraordinary abatement measures on a case-by-case basis. When considering extraordinary abatement measures, the State must demonstrate that the affected activities experience traffic noise impacts to a far greater degree than other similar activities adjacent to highway facilities, e.g, residential areas with absolute noise levels of 75 dBA Leq(h) or more, residential areas with noise level increases of 30 dBA or more over existing noise levels. Examples of extraordinary abatement measures would be the noise insulation of private residences or the purchase of private dwellings from willing sellers.

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:

  1. 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,
  2. Information that may be useful to local communities to protect future land development from becoming incompatible with anticipated highway noise levels, and
  3. eligibility for Federal-aid participation for Type II projects as described in paragraph 772.13b of this directive.

    The prevention of future impacts is one of the most important parts of noise control. The compatibility of the highway and its neighbors is essential for the continuing growth of local areas. Both development and highways can be compatible. But, local government officials need to know what noise levels to expect from a highway and what techniques they can use to prevent future impacts. States can help by providing this information to local governments; such information should be made available for disclosure in real estate transactions.

    Highway traffic noise should be reduced through a program of shared responsibility. Thus, the FHWA encourages State and local governments to practice compatible land use planning and control in the vicinity of highways. Local governments should 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. Local officials should be made aware of the requirement for the adoption of an active noise-compatible land use control program for approval of Type II abatement (see paragraph 772.13b on page 16).


  1. Any traffic noise prediction method is approved for use in any noise analysis required by this directive if it generally meets the following two conditions:
    1. The methodology is consistent with the methodology in the FHWA Highway Traffic Noise Prediction Model (Report No. FHWA-RD-77-108).
    2. The prediction method uses noise emission levels obtained from one of the following:
      1. National Reference Energy Mean Emission Levels as a Function of Speed (Figure 1).
      2. Determination of reference energy mean emission levels in "Sound Procedures for Measuring Highway Noise: Final Report," Report No. DP-45-1R.
  2. 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.

    Most States use the FHWA highway traffic noise prediction model (FHWA model) with its national emission levels. If a State uses different emission levels, documentation must be provided to the FHWA Division Office to justify its use. Paragraph 772.17a(2)(b) specifies that the method in Report No. DP-45-1R be used to obtain these emission levels. The FHWA Division Office should forward the proposed emission levels to FHWA Headquarters for review and comment. Some States have modified computer versions of the FHWA model to change input/output characteristics to suit the State's design process.

    Traffic characteristics used in predicting future noise levels could make a substantial difference in the results. "Worst hourly traffic noise impact" occurs at a time when truck volumes and vehicle speeds are the greatest, typically when traffic is free-flowing and at or near level of service C conditions. The numbers of medium and heavy trucks are very important.

    SHAs should use either the posted speed limit or the operating speed (highest overall speed at which a driver can travel on a given highway under favorable weather conditions and under prevailing traffic conditions, without at any time exceeding the safe speed as determined by the design speed on a section-by-section basis) to predict traffic noise levels. SHAs are required to use the operating speed if it is determined to be consistently higher than the posted speed limit. In determining the operating speed along an existing highway, the first step is to identify the time period during which the worst traffic noise impacts are expected to occur. Then, the speed may be determined by actually driving a vehicle in the traffic stream and recording the average speed. It may also be determined by using radar meters or other devices to measure speeds at a point along the highway (making no adjustments to the actual instrument measurements). Such measured speeds are then arithmetically averaged to calculate a time mean speed (as defined in Highway Capacity Manual: Special Report 209). Either the "traffic stream" speed or the time mean speed can be used to represent the operating speed.


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

  1. 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.
  2. 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.
  3. Incorporate the needed abatement measures in the plans and specifications.

The impact of construction noise does not appear to be serious in most instances. FHWA Technical Advisory T 6160.2, "Analysis of Highway Construction Noise," outlines procedures for the analysis of highway construction noise. The following items should be considered to ensure that potential construction noise impacts are given adequate consideration during highway project development:

  1. Calculation of construction noise levels is usually not necessary for traffic noise analyses. If a construction noise impact is anticipated at a particular sensitive receptor, use of the model contained in "Highway Construction Noise: Measurement, Prediction, and Mitigation" to predict construction noise levels should be sufficient. The computerized prediction model HICNOM is quite sophisticated and requires considerable input, and, therefore, should be used only on highly complex or controversial major urban projects.
  2. Potential impacts of highway construction noise should be addressed in a general manner for traffic noise analyses. The temporary nature of the impacts should be noted. An indication of the types of construction activities that can be anticipated and the noise levels typically associated with these activities can be obtained from existing literature and presented in the noise analysis.
  3. Utilizing a common-sense approach, traffic noise analyses should identify measures to mitigate potential highway construction noise impacts. Low-cost, easy-to-implement measures should be incorporated into project plans and specifications (e.g., work-hour limits, equipment muffler requirements, location of haul roads, elimination of "tail gate banging," reduction of backing up for equipment with alarms, community rapport, complaint mechanisms).
  4. Major urban projects with unusually severe highway construction noise impacts require more extensive analyses. Sensitive receptors should be identified, existing noise levels should be measured, construction noise levels should be predicted, and impacts should be discussed so as to properly indicate their severity. Mitigation measures likely to be incorporated into these projects may be quite costly and should be thoroughly discussed and justified in the analyses. The use of portable noise barriers and special quieting devices on construction equipment have been used for construction noise mitigation.

This figure shows each reference energy mean emission levels as a function of speed (50mph to 100 mph) and decibel levels (55 dBA to 95 dBA) for automobiles, medium trucks and heavy trucks.
Figure 1: Reference Energy Mean Emission Levels

Updated: 8/24/2017
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