127.13 Noise

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Additional Information
23 CFR 772
Procedures for Abatement of Highway Traffic Noise and Construction Noise
FHWA Analysis and Abatement Guidance

This article contains the MoDOT noise policy on highway traffic noise and construction noise and describes MoDOT's implementation of the requirements of the Federal Highway Administration (FHWA) Noise Standard at 23 Code of Federal Regulations (CFR) Part 772. This policy was developed by MoDOT and approved by FHWA.

The primary sources of highway traffic noise are the tire-pavement interface, engine noise and exhaust noise. In very general terms, the lower threshold of highway noise impact is roughly the point at which interference with normal human speech is appreciable.

The 1972 Federal-aid Highway Act required FHWA to develop a noise standard for new Federal-aid highway projects. FHWA Noise Standards give highway agencies flexibility in conforming to national requirements.

This article presents MoDOT’s policy on how highway traffic noise impacts are defined, how noise abatement is evaluated and how noise abatement decisions are made. Noise abatement measures that are found to be feasible and reasonable must be constructed for such projects. Feasible and reasonable noise abatement measures are eligible for Federal-aid participation at the same ratio or percentage as other eligible project costs.

Contents

127.13.1 Purpose

MoDOT’s program to implement 23 CFR 772 is defined herein. Where FHWA has given MoDOT flexibility in implementing the standard, this policy describes MoDOT’s approach to implementation. Per FHWA, changes go into effect on July 13, 2011. The old policy will apply to projects that have reached the practicable alternatives stage or beyond by this date. This article will apply to projects not developed to that stage.

127.13.2 Noise Standards

This article outlines MoDOT’s program to implement the FHWA Noise Standards found at 23 CFR 772. They include traffic noise prediction requirements, noise analyses, noise abatement criteria and requirements for informing local officials.

127.13.3 Definitions

Abatement, Measures used to mitigate or reduce traffic noise impacts.

Activity Category A, 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.

Activity Category B, Exterior areas of single-family and multi-family domiciles.

Activity Category C, Exterior areas of non-residential land uses including active sport areas, amphitheaters, auditoriums, campgrounds, cemeteries, day care centers, hospitals, libraries, medical facilities, parks, picnic areas, places of worship, playgrounds, public meeting rooms, public or nonprofit institutional structures, radio studios, recording studios, schools and television studios.

Activity Category D, Interior areas of the following land uses: Auditoriums, day care centers, hospitals, libraries, medical facilities, places of worship, public meeting rooms, public or nonprofit institutional structures, radio studios, recording studios, schools and television studios.

Activity Category E, Exterior areas of developed lands that are less sensitive to highway traffic noise. These land uses include: Hotels, motels, offices, restaurants/bars, and other developed lands, properties or activities not included in A-D or F.

Activity Category F, Land uses that are not sensitive to highway traffic noise. These land uses include: Agriculture, airports, bus yards, emergency services, industrial, logging, maintenance facilities, manufacturing, mining, rail yards, retail facilities, shipyards, utilities (water resources, water treatment, electrical) and warehousing.

Activity Category G, Undeveloped lands.

Approach, Noise levels representing the worst traffic hour, L(h), which are 1 decibel (dBA) below the levels in the Noise Abatement Criteria Table.

Barrier, A solid wall or combination of an earthen berm and wall to provide traffic noise reduction for impacted receptors.

Benefitted Receptor, A receptor that receives at least a 7 dBA reduction in noise level after the addition of noise abatement measure(s).

Berm, Earthen structure constructed to provide a traffic noise reduction for impacted receptors. Noise berms and noise barriers may be combined to provide noise abatement.

Categorical Exclusions (CE), The National Environmental Policy Act (NEPA) classification for projects with minimal environmental impacts.

CFR, Code of Federal Regulations.

Date of Public Knowledge, -- The date of approval of the Categorical Exclusion (CE), the Finding of No Significant Impact (FONSI), or the Record of Decision (ROD), as defined in CFR part 771.

dBA, A weighted decibel, unit corrected to best measure/express the relative loudness of sounds in air as perceived by the human ear.

Design Year, The future year used to estimate the probable traffic volume for which a highway project is designed, typically 20 years into the future.

Environmental Analysis (EA), The NEPA classification given to projects where the significance of impacts are not clear and are intermediate between the complexity of Environmental Impact Statements and the simplicity of CEs.

Environmental Impact Statement (EIS), The most detailed of NEPA classifications. EISs are usually applied to the largest scale highway projects where significant impacts are expected.

Existing Noise Level, The noise resulting from natural, manmade sources and human activity considered to be usually present in a particular area.

Feasibility, Consideration of engineering factors and other constraints as they related to construction of noise abatement.

Finding of No Significant Impact (FONSI), Acceptance document signifying the completion of a final EA by the federal agency.

Impacted Receiver/Receptor, Any receiver that has an Leq at the loudest traffic noise hour approaching (within 1 dB) or exceeding the Noise Abatement Criteria Table for the corresponding land use category, or exceeding existing noise levels by 15 dBA.

Insertion Loss, The difference between an evaluated receptor’s Leqs with and without the barrier (barrier level minus no barrier level).

Leq, The equivalent steady-state sound level at a given time. Very simplistically this is sound exposure level.

Leq(h), The hourly value of Leq.

Multifamily Dwelling, A residential structure containing two or more residences. Each residence in a multifamily dwelling shall be counted as one receptor when determining impacted and benefited receptors.

NAC, The Noise Abatement Criteria as shown in the Noise Abatement Criteria Table. These are absolute noise levels for each activity category at or above which a noise impact is indicated.

Receiver/Receptor, A discrete or representative location of a noise sensitive area(s), for any of the land uses listed in the Noise Abatement Criteria Table.

Records of Decision (ROD), Documentation that signifies acceptance of a final EIS by the federal agency.

Representative Receptor, A point or receptor that best represents the acoustic environment of a group of receptors.

Substantially exceed the existing noise levels, Increases of 15 dBA above the existing noise level are considered to be substantial by MoDOT.

Traffic Noise Impacts, Impacts that occur when the predicted traffic noise levels approach or exceed the NAC or when the predicted traffic noise levels substantially exceed the existing noise levels.

Type I Project,

1. The construction of a highway on new location; or,
2. The physical alteration of an existing highway where there is either:
a. Substantial Horizontal Alteration. A project that halves the distance between the traffic noise source and the closest receptor between the existing condition to the future build condition; or,
b. Substantial Vertical Alteration. A project that removes shielding (vegetation does not constitute shielding as it typically does not provide substantial noise reduction), as it thereby exposes the line-of-sight between the receptor and the traffic noise source (maintenance and resurfacing projects are not Type I projects). This is done by either altering the vertical alignment of the highway or by altering the topography between the highway traffic noise source and the receptor; or,
3. The addition of a through-traffic lane(s). This includes the addition of a through-traffic lane that functions as an High Occupancy Vehicle (HOV) lane, High Occupancy Toll (HOT) lane, bus lane, or truck climbing lane; or,
4. The addition of an auxiliary lane, except for when the auxiliary lane is a turn lane; or,
5. The addition or relocation of interchange lanes or ramps added to a quadrant to complete an existing partial interchange; or,
6. Restriping existing pavement for the purpose of adding a through-traffic lane or an auxiliary lane; or,
7. The addition of a new or substantial alteration of a weigh station, rest stop, ride-share lot or toll plaza.
8. If any portion of a project evaluated under NEPA is determined to be Type I per 23 CFR 772.5, then the entire project area as defined in the environmental document is a Type I project.

Type II Project, A proposed Federal or Federal-aid highway noise abatement retrofit project on an existing highway. Type II projects result from situations that predate highway noise regulation or adjacent developments that occur after highway construction.

Type III Project, A proposed Federal or Federal-aid project that does not meet the criteria for Type I or Type II is designated as a Type III project. Type III projects do not require noise analysis. Examples of Type III projects are rehabilitations, bridge replacements, shoulder additions, and turning lanes.

127.13.4 Applicability

This article applies to all Type I Federal highway projects in Missouri; that is, any project that receives Federal-aid funds or is otherwise subject to FHWA approval. They include Federal projects that are administered by Local Public Agencies (LPAs) as well as the highway agency.

If there are any questions about whether a project is subject to this policy or the FHWA Noise Standard, contact MoDOT’s Environmental Section. Because of the long lead time to complete a traffic noise study, emphasis should be placed on determining the need for a noise study early in project scoping.

MoDOT does not participate in a Type II noise program.

127.13.5 Traffic Noise Prediction

The FHWA Traffic Noise Model, TNM 2.5, or the most recent version of TNM, will be used to predict traffic noise. Other models found acceptable to FHWA and pursuant to 23 CFR 772.9 may be proposed and will be evaluated on a case by case basis. Traffic noise predictions will be performed for all reasonable build alternatives under consideration in NEPA documents for Type I projects.

Average pavement type will be used in all models, unless MoDOT obtains FHWA approval to use different pavement type(s).

The worst traffic noise hour will be used in noise predictions. This period is usually preceding or after the peak traffic period. Due to congestion and the resulting slowing of traffic, noise levels usually decrease and large, noisy, trucks often avoid the peak traffic period.

127.13.6 Analysis of Traffic Noise Impacts

Although traffic noise measurements are sufficient in determining existing traffic noise levels, a combination of measurements and modeling can serve to validate the model for the existing condition as well. The combination is preferred. Further instructions may be found at FHWA-PD-96-046 DOT-UNTSC-FHWA-96-5.

Noise readings must be taken at representative receptor locations for proposed highway projects on new alignment, where no highway exists.

Measurements should be taken during the worst noise hour. This corresponds usually to the period preceding or just after the peak traffic volume, in heavily congested urban areas. This is largely because of slow peak traffic speeds and large trucks avoiding congested periods. Measurements should not be taken during rain events or in winds exceeding twelve miles per hours. Measurements will conform to FHWA requirements, FHWA-PD-96-046 DOT-UNTSC-FHWA-96-5.

ANSI Type 1 or 2 integrating sound level meters are required. FHWA guidance will be used, FHWA-PD-96-046 DOT-UNTSC-FHWA-96-5.

MoDOT’s standard procedure for validating traffic noise models is a comparison of existing noise levels and predicted noise levels, for the existing traffic condition. If the levels are within three decibels for selected receptors, the model is assumed to be valid.

Outdoor areas of frequent human use are considered primary locations when determining noise impact and will be used for taking noise readings. Play areas, balconies, swimming pools and patios are examples of frequent human use areas. Engineering judgment must be exercised in determining which, if multiple frequent human use areas are present, is potentially most affected by highway noise.

For NEPA documents on Type I projects, noise analysis is required for all reasonable build alternatives. Lesser evaluations may be appropriate for examination of broad corridors, such as Tier 1 Environmental Impact Statements, provided there is early FHWA and participating agency agreement.

If any segment or component of an alternative meets the definition of a Type I project, then the entire alternative is considered to be Type I and is subject to the noise analysis requirements early in the project planning process.

Noise analysis must include each Activity Category present in the study area. See Noise Abatement Criteria Table for additional details on each Activity Category.

Activity Category A Justifications for designating land as Category A will be submitted through the Missouri FHWA Division Office and FHWA Headquarters, as this is the protocol outlined by FHWA, per 23 CFR 772.11. Impacts are either a substantial increase, 15 dBA or approaching the NAC, 56 dBA.

Activity Category B Each potentially affected receptor will be analyzed for traffic noise impact, which would be a substantial increase, 15 dBA or greater, or approaching the NAC, 66 dBA.

Activity Categories C Each potentially affected property will be analyzed for traffic noise impact, which would be a substantial increase, 15 dBA or greater, or approaching the NAC, 66 dBA. Receptors will be counted as feet of frontage, which will be the average of the residential frontages in the project area (e.g. one receptor equals 100 ft. of frontage).

Activity Category D This Category should only be used after exhausting all outdoor analysis options. Each potentially affected property will be analyzed for traffic noise impacts, which would be a substantial increase, 15 dBA or greater, or approaching the NAC, 51 dBA. Receptors will be counted as feet of frontage, which will be the average of the residential frontages in the project area (e.g. one receptor equals 100 ft. of frontage). FHWA publication FHWA-DP-45-1R, Sound Procedures for Measuring Highway Noise: Final Report provides procedures to measure building noise reductions.

Activity Category E Each potentially affected property will be analyzed for traffic noise impact, which would be a substantial increase, 15 dBA or greater, or approaching the NAC, 71 dBA. Receptors will be counted as feet of frontage, which will be the average of the residential frontages in the project area (e.g. one receptor equals 100 ft. of frontage).

Activity Category F No action required.

Activity Category G Representative data will be generated as needed to provide information to other governmental entities.

Approaching NAC is defined by MoDOT as being 1 dBA less than the NAC for Activity Categories A-E.

A substantial increase over the existing noise level is an increase of at least 15 dBA. This level of increase is difficult to achieve. Generally, this sort of impact would only be expected for larger highways on new alignment or new highways.

As previously noted, MoDOT does not participate in a Type II noise abatement program. If a local government commits to complete a noise abatement project on a MoDOT roadway, they may petition the Missouri Transportation and Highway Commission to fund 25 percent of the cost. Proposed projects must meet all MoDOT noise impact and abatement criteria. No federal funds are available for use in these situations.

Impacted receptors will usually be identified by ID numbers given during noise analysis. These ID numbers will correspond to a physical address.

127.13.7 Analysis of Noise Abatement Measures

When traffic noise impacts are identified, noise abatement shall be considered and evaluated for feasibility and reasonableness.

Noise barriers are most often used as noise abatement. However, all potential noise abatement measures may be considered and used if they are both feasible and reasonable.

At this time, MoDOT is not a part of a FHWA-approved Quiet Pavement Pilot Program. Therefore, use of quieter pavements is not an acceptable Federal-aid noise abatement measure for Federal projects. Use of vegetation or landscaping is not an acceptable Federal-aid noise abatement measure. For vegetative noise attenuation to be appreciable a minimum of a 100-ft. buffer is required and only dense evergreen vegetation is effective. Use of absorptive materials will be considered, if circumstances warrant its use.

127.13.8 Feasibility

Feasibility is the ability to provide abatement in a given location considering the acoustic and engineering limitations of the site. Acoustic feasibility refers to noise abatement measure(s) ability to achieve the minimum noise reduction at impacted receptors. MoDOT requires at least a 5 dBA insertion loss for a minimum of 67 percent of first-row, impacted receivers for noise abatement to be considered feasible. Engineering feasibility refers primarily to physical constraints and other constuctability constraints, such as topography, access, drainage, safety, maintenance, and presence of other noise sources. In general, if these factors are too extreme or cannot be accommodated in providing the minimum noise reduction, noise abatement will be deemed unfeasible. For reasons of safety (primarily wind load and clear space concerns), a noise wall's height is limited to 20 feet. This criterion alone cannot be used to consider noise abatement unreasonable.

127.13.9 Reasonableness

Each of the three required reasonableness factors must be met.

Mandatory Reasonableness Factors:

1. Viewpoints of owners and residents of the benefitted receptors will be obtained. These will usually be obtained through mailings or a public forum. The viewpoints of non-owner residents will be evaluated as a portion of an aggregate of 25 percent of the total. The viewpoints of owners will be evaluated as a portion of an aggregate of 75 percent of the total. For noise abatement to be considered reasonable, over 50 percent of the aggregate response must be in favorable.
2. Noise abatement measures shall not exceed 1,300 square feet per benefitted receptor, in the case of noise walls. Where noise walls are not options, other noise abatement techniques may be considered, but cannot exceed $36,000 per benefitted receptor. In order to ensure that the noise abatement parameters remain current, the wall area limit and cost per benefited receptor shall be recalculated at an interval not to exceed every five years. The updated values may not be used to analyze noise abatement calculations from previous years.
3. Noise abatement measures must provide a benefit of a minimum of 7 dBA for 67 percent of benefitted first-row receptors.

For reasons of safety (primarily wind load and clear space concerns), noise walls are limited to a height of 20 feet. This criterion alone cannot be used to consider noise abatement unreasonable.

For noise abatement measure reporting (23 CFR 772.13(f)), MoDOT shall maintain an inventory of all constructed noise abatement measures. The inventory shall include the following parameters: type of abatement; cost (overall cost, unit cost per sq. ft.); average height; length; area; location (State, county, city, route); year of construction; average insertion loss/noise reduction as reported by the model in the noise analysis; NAC category(s) protected; material(s) used (precast concrete, berm, block, cast in place concrete, brick, metal, wood, fiberglass, combination, plastic (transparent, opaque, other); features (absorptive, reflective, surface texture); foundation (ground mounted, on structure); project type (Type I, Type II); and optional project types such as state, county, tollway/turnpike, or other unknown funding sources. This information shall be collected triennially by the design division.

NEPA Decision: Prior to a CE approval or issuance of a FONSI or ROD for a Type I project, the highway agency must identify:

1. The noise abatement measures that are feasible, reasonable, and likely to be incorporated into the project; and
2. Noise impacts for which no abatement appears to be feasible and reasonable;
3. The NEPA documentation for Type I projects shall identify the locations where noise impacts will occur, where noise abatement is feasible and reasonable, and the locations that have no feasible and reasonable abatement. The statement of likelihood will include the preliminary locations of feasible and reasonable abatement and a statement that the final recommendation will be made after the final design and public involvement processes are complete. For example: Noise walls are very likely between stations 41+00 and 42+00 and should average 12 feet. The noise walls will attenuate noise on the south side of the highway. The noise walls appear to be both reasonable and feasible. Final recommendations will be made after final design and the public involvement are complete.

Third party funding cannot be used to make up the difference in cost between the reasonable cost allowance and the actual cost. Third party funding can only be used to pay for additional features such as landscaping, aesthetic treatments, etc. for noise barriers that meet cost-effectiveness criteria.

MoDOT does not allow cost averaging.

127.13.10 Noise Wall Public Meeting and Voting

Noise Wall Ballot
For Use in Public Meetings Statewide
Official Ballot

For projects with noise impacts where noise abatement is both reasonable and feasible, a noise wall public meeting is required. If project timing allows, this meeting can be combined with other project public meetings. Required invitees for this meeting are all first-row and benefitted receptors. However, a meeting with non-qualifying impacted area residents is sometimes beneficial. Meeting with different groups of residents can be combined where appropriate.

In most cases, ballots are sent to all first-row and benefitted receptors prior to the public meeting. This practice allows deliberation and the opportunity to ask questions and turn in ballots at the public meeting. A simple majority is required to qualify a noise wall.

127.13.11 Federal Participation in Type I and Type II Projects

Federal funds may be used for noise abatement measures when:

1. Traffic noise impacts have been identified; and
2. Abatement measures have been determined to be feasible and reasonable pursuant to 23 CFR 772.13(d).

127.13.12 Information for Local Government Officials

To minimize future traffic noise impacts on currently undeveloped lands for Type I projects, MoDOT shall inform local officials within whose jurisdiction the highway project is located of:

1. Noise compatible planning concepts;
2. The best estimation of the distance to future design year noise levels that approach the exterior noise abatement criteria in Noise Abatement Criteria Table;
3. Non-eligibility for Federal-aid participation for a Type II project as described in 23 CFR 772.15(b), for developments in areas shown to be noise impacted.

127.13.13 Construction Noise

For all Type I and II projects, MoDOT will as required in 23 CFR 772.19:

1. Identify land uses or activities that 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 that 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 costs of the abatement measures.
3. Incorporate the needed abatement measures in the plans and specifications.

127.13.14 Part 772 Noise Abatement Criteria Table

Activity CategoryActivity Criteria1 Evaluation Location Activity Description
Leq(h)L10(h)
A 57 60 ExteriorLands 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
B26770 Exterior Residential
C 6770ExteriorActive sport areas, amphitheaters, auditoriums, campgrounds, cemeteries, day care centers, hospitals, libraries, medical facilities, parks, picnic areas, places of worship, playgrounds, public meeting rooms, public or nonprofit institutional structures, radio studios, recording studios, recreation areas, Section 4(f) sites, schools, television studios, trails and trail crossings
D 5255InteriorAuditoriums, day care centers, hospitals, libraries, medical facilities, places of worship, public meeting rooms, public or nonprofit institutional structures, radio studios, recording studios, schools, and television studios
E27275ExteriorHotels, motels, offices, restaurants/bars, and other developed lands, properties or activities not included in A-D or F
F- --Agriculture, airports, bus yards, emergency services, industrial, logging, maintenance facilities, manufacturing, mining, rail yards, retail facilities, shipyards, utilities (water resources, water treatment, electrical) and warehousing
G---Undeveloped lands that are not permitted for development
1 The Leq(h) and L10(h) Activity Criteria values are for impact determination only, and are not design standards for noise abatement measures.
2 Includes undeveloped lands permitted for development for this activity category.
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