127.13 Noise

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This article presents MoDOT’s noise policy on highway traffic and construction noise impacts. It outlines the evaluation and decision making process for noise abatement in accordance with 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.

MoDOT uses this policy to consider highway traffic noise impacts to comply with the National Environmental Policy Act (NEPA).

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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.

During the rapid expansion of the interstate highway system and other roadways in the 20th century, communities began to recognize that highway traffic noise and construction noise had become important environmental impacts. Passage of the 1972 Federal-aid Highway Act required FHWA to develop a noise standard for new Federal-aid highway projects. While providing national criteria and requirements for all highway agencies, the FHWA Noise Standards give highway agencies flexibility that reflects state-specific attitudes and objectives in approaching the problems of highway traffic and construction noise.

In addition to defining traffic noise impacts, the FHWA Noise Standards require that noise abatement measures be considered when traffic noise impacts are identified for Type 1 Federal projects. 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.

127.13.1 Purpose

FHWA has given MoDOT flexibility in implementing the noise standard; this policy describes MoDOT’s approach to implementation of 23 CFR 772.

127.13.2 Noise Standards

This article outlines MoDOT’s program to implement the FHWA Noise Standards found in 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.

Ambient Noise, All-encompassing sound that is associated with a given environment.

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

Attenuation, Reduction of the level of sound or noise.

Average Daily Traffic (ADT), the average 24 hour volume, being the total volume during a stated period divided by the number of days in that period. Normally, this would be periodic daily traffic volumes over several days, not adjusted for days of the week or seasons of the year.

Average Annual Daily Traffic (AADT), the total volume of traffic passing a point or segment of a highway facility in both directions for one year divided by the number of days in the year. Normally, periodic daily traffic volumes are adjusted for hours of the day counted, days of the week, and seasons of the year to arrive at average annual daily traffic.

A-Weighted Sound Level (dBA), The sound level in decibels that correlates to the inverted Fletcher & Munson 40-phon curve measuring loudness. The A-scale tends to suppress lower frequencies (e.g. below 1,000 Hertz) and best approximates the sound as heard by the human ear.

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.

Common Noise Environment, A group of receptors within the same Activity Category in Noise Abatement Criteria Table that are exposed to similar noise sources and levels, traffic volumes, traffic mix and speed and topographic features. Generally, common noise environments occur between two secondary noise sources, such as interchanges, intersections or crossroads and within the same or very similar developments.

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.

Decibel (dB), a measure used to express the relative level of a sound in comparison with a standard reference level. For traffic noise purposes, the A-weighted scale, which closely approximates the frequency response of the human ear to typical environmental sound levels, is used. The A-weighted sound level in decibels has the unit dBA.

Design Hour Volume (DHV), the DHV is typically the thirtieth highest hourly traffic volume (30HV) for the design year, commonly twenty years from the time of construction. The DHV is given in units of vehicles per hour.

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 Assessment (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, One of two criteria (also see “Reasonableness”) used to evaluate a noise abatement measure for installation. Feasibility is the consideration of engineering factors and other constraints as they relate to construction of noise abatement.

Finding of No Significant Impact (FONSI), If it is determined that there will be no significant impacts, a finding of no significant impact (FONSI) will be prepared to conclude the process and document the decision. A FONSI is issued when environmental analysis and interagency review during the EA process find a project to have no significant impacts on the quality of the environment. "Human Environment" includes the natural and physical environment and the relationship of people with the environment.

First-Row Receptors, Receptors directly adjacent to the highway, at nearly the same elevation, with no intervening developed lands. Receptors with intervening parcels separating the receptor parcel from abutting the roadway right-of-way are generally considered second row or greater.

Frequent Human Use, Any activity that results in prolonged human exposure to traffic noise on a regular basis over the course of a year in a given location.

Future Noise Level, The predicted worst one-hour equivalent sound level in dBA in the design year.

Impacted Receiver/Receptor, Any receiver that has an Leq at the loudest traffic noise hour approaching (within 1 dB) or exceeding the Leq as shown in 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).

LAeq, the A-weighted equivalent steady-state sound level that in a stated period of time contains the same acoustic energy as the time-varying sound level during the same time period.

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.

NEPA, The National Environmental Policy Act.

Noise, Unwanted sound.

Noise Barrier, A physical obstruction that is constructed between the highway noise source and the noise sensitive receptor(s) that lowers the noise level, including stand-alone noise walls, noise berms (earth or other material) and combination berm/wall systems.

Noise Reduction Design Goal, The predicted minimum noise level reduction provided by the noise abatement measure. MoDOT’s noise reduction design goal is 7 dBA and must be achieved for all first-row benefited receptors. If a reduction of 7 dBA for all first-row benefited receptors cannot be met, the abatement measure would not be considered reasonable.

Permitted, A definite commitment to develop land with an approved specific design of land use activities as evidenced by the issuance of a building permit.

Property Owner, An individual who or group of individuals that holds a title, deed or other legal documentation of ownership of a property or residence.

Reasonableness, One of two criteria (also see “feasibility”) used to evaluate a noise abatement measure for installation. Reasonableness weighs the amount of required noise barrier area against the benefits that would be provided by the barrier.

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.

Residence, Either a single family residence or each dwelling unit in a multifamily dwelling.

Shielding, Any man-made or natural structure or barrier that provides an auditory barrier between a receptor and a roadway. For example, the top of a cut or an intervening hill. Vegetation does not qualify since it does not provide substantial noise reduction.

Sound Level Meter, A device used to measure sound levels. A sound level meter is also called a sound level analyzer or dosimeter.

Statement of Likelihood, A statement regarding the likelihood of abatement, provided in the environmental clearance document based on the feasibility and reasonableness analysis completed at the time the environmental document is being approved.

Substantial Increase Over Existing Noise Levels, Increases of 15 dBA above the existing noise level are considered to be substantial.

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.

Worst Noise Hour, A one-hour period during the day that represents the peak noise hour.

127.13.4 Applicability

This policy 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.

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.

Noise contour lines may be used for project alternative screening or land use planning purposes only. Determination of highway traffic noise impacts will require a full highway traffic noise study outlined by this policy and MoDOT’s Noise Procedures.

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. Peak traffic periods typically result in lower noise levels due to slower traffic speeds and the absence of large, noisy trucks avoiding the traffic congestion.

127.13.6 Analysis of Traffic Noise Impacts

Per 23 CFR 772 and EPG 127.13 Noise, noise studies must be conducted for highway projects that are determined to be Type I.

As outlined in the definitions, Type I projects are proposed Federal-aid projects for the construction of a highway on new location or the physical alteration of an existing highway that significantly changes either the horizontal or vertical alignment or increases capacity.

A project that horizontally halves the distance between the traffic noise source and the closest receptor or vertically exposes the receptor’s line of sight to the noise source are considered Type I projects. When assessing whether a project will halve the distance between the noise source and a receptor, the measured distance will be the smallest distance between the receptor and the center of the nearest travel lane.

MoDOT is required by federal law to evaluate noise abatement for new highway construction and widening projects. However, there is no federal requirement for state DOTs to construct noise barriers along existing highways adjacent to developments that are built after highway construction or predate highway noise regulations. Such stand-alone "retrofit" noise barrier projects are referred to as Type II projects. MoDOT does not participate in a Type II noise program.

Noise Screening Analysis

Some Type I projects have very low potential to create noise impacts and could benefit from a noise screening analysis. A screening analysis is generally completed for projects where noise impacts are not anticipated.

The screening analysis is a simple procedure used to predict traffic noise levels and make a practical determination of noise impacts. There are limitations to the screening procedures, and they are not applicable to all projects. If the results of a screening analysis indicate that noise impacts are likely and the placement of typical abatement devices appears to be feasible, a detailed analysis would be required. A screening analysis should be performed using a simplified FHWA Traffic Noise Model (TNM) run to assess the worst-case conditions.

If impacts are noted and abatement is clearly NOT feasible (e.g., driveway access), the screening procedures should suffice and a detailed noise analysis would not be required. However, impacts and the rationale behind the feasible determination must be documented in the NEPA document through the noise technical report, with supporting documentation attached. All requirements, including reporting requirements, of 23 CFR 772 still must be met. Field measurements may be required to justify the results when the screening analysis has identified impacts, and feasible abatement appears unlikely.

If there are areas in a corridor where the screening analysis has identified impacts, and feasible abatement is likely, the process outlined in EPG 127.13.7 Analysis of Noise Abatement Measures and EPG 127.13.12 MoDOT Procedures for Assessment and Abatement of Highway Traffic and Construction Noise shall be followed for that area.

Existing Noise Levels

Noise levels must be evaluated using one of the following methods:

  • Method 1: Measurement of Existing Noise Levels
  • Method 2: Prediction of Existing Noise Levels
  • Method 3: Measurement and Prediction of Existing Noise Levels (including validation)

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. Method 3 is preferred. The sole use of Methods 1 or 2 will require acceptance from MoDOT’s Environmental Section. Further instructions may be found at 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.

Measurements

Similarly to noise predictions, measurements must be taken at representative receptor locations 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 peak traffic speeds are slower and large trucks avoid 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. Safety of the traveling public and field staff conducting noise measurements must be maintained in accordance with MoDOT’s safety policy. When measurements are taken within the right-of-way, or in the vicinity of vehicular traffic, high-visibility safety apparel that meets the current ANSI 107 standard shall be used. Permission from landowners shall be obtained before any noise measurements are conducted off MoDOT right of way.

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. However, the appropriate noise analysis method should be applied depending upon the potential for impacts and abatement. A combination of methods may be applicable within an alternative.

Noise analysis must include each Activity Category present in the study area. See Table 127.13.6, Noise Abatement Criteria, for additional details on each Activity Category.

Traffic noise impacts may occur when either the predicted noise level at a receptor approaches or exceeds the NAC or when there is a substantial increase in noise as a result of the project. Approaching NAC is defined by MoDOT as being 1 dBA less than the NAC for Activity Categories A-E. Highway traffic noise impacts will be considered substantial if they increase 15 dBA above the existing noise level.

Table 127.13.6, Noise Abatement Criteria

Activity Category Activity Criteria1 Evaluation Location Activity Description
Leq(h) L10(h)
A 57 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
B2 67 70 Exterior Residential
C 67 70 Exterior 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, recreation areas, Section 4(f) sites, schools, television studios, trails and trail crossings
D 52 55 Interior 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
E2 72 75 Exterior Hotels, 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.

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, in 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 Category 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.

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. 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.

Activity Category F. No action required, except as noted in Activity Category G.

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

Category G land uses are undeveloped lands that should be addressed as part of EPG 127.13.12.2.11 Information for Local Officials. Lands used for agriculture that are included in Category F also should be addressed in EPG 127.13.12.2.11 Information for Local Officials section of the noise study report.

Traffic noise analysis should be performed for developed lands containing noise-sensitive land uses, and for undeveloped lands where noise-sensitive development is permitted. A development is deemed to be “permitted” if there is a definite commitment to develop land with an approved specific design as evidenced by the issuance of a building permit. The municipal planning or codes department should be contacted to determine if any building permits have been issued in the project area.

The noise study should include lands for which development is “permitted” at the date of public knowledge for the project. The date of public knowledge is the date that a project’s final environmental document (i.e. CE, FONSI, or ROD) is approved by FHWA.

Federal participation in noise abatement measures will not be considered for lands that are not permitted by the date of public knowledge of the project, and MODOT will not analyze or provide noise abatement for these lands. After the date of public knowledge, provision of noise abatement becomes the responsibility of local communities or private developers.

Noise Abatement Options

Noise abatement should be evaluated when noise impacts are predicted in the design year for the Build Alternative(s). At a minimum, MoDOT will consider noise abatement in the form of a noise barrier, since barriers are generally the best available abatement measure to reduce sound levels for impacted land uses. Noise abatement measures shall not exceed 1,300 square feet per benefitted in the case of noise walls. Where noise walls are not an option, other abatement techniques may be considered, but cannot exceed $46,000 per benefitted receptor.

Alternate abatement techniques such as earth berms are similar to noise barriers, and are sometimes considered to be more aesthetically pleasing than noise barriers. However, berms require significant right-of-way that is typically not available. For example, the width of a 15-ft. tall berm constructed at a 2:1 (1V:2H) slope with a top flat width of 5 ft. is 65 ft. plus additional width for drainage. Additionally, berms are generally not feasible where the road is in cut or on-fill. Earth berms also may be difficult to maintain. Therefore, earth berms are not feasible for most projects. As a result, berms will be evaluated on a case-by-case basis in lieu of or in combination with noise barriers.

If an existing earth berm in MoDOT right of way is modeled and found to be a barrier to the level that receptor(s) are below the impact threshold, the berm should be maintained to the extent possible.

Final Noise Abatement Decisions

Conditions can change during the project design process. This may result in a reevaluation of NEPA for a proposed project, including a review of the noise policy application. These changes may affect the preliminary noise abatement determinations in the environmental document. Such changes could include modifications to the proposed cross-sections, shifting the alignment, and changing roadway or ramp grades. New noise abatement determinations will require a public record documentation and approval from FHWA. The noise policy in effect at the time of the reevaluation will be used to make abatement decisions.

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.

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 2 first-row, impacted receivers for noise abatement to be considered feasible. Engineering feasibility refers primarily to physical constraints and other constructability 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 infeasible. For reasons of safety (primarily wind load and clear space concerns), a noise wall's height is limited to 20 feet. The wall height criterion alone cannot be used to consider noise abatement infeasible.

Reasonableness

Each of the three required reasonableness factors listed below must be met.

Mandatory Reasonableness Factors:

1. Viewpoints of owners and residents of the benefitted receptors will be obtained. These will usually be obtained by ballot through mailings or at a public forum;
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 $46,000 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. MoDOT does not allow cost averaging; and
3. Noise abatement measures must provide a minimum reduction of 7 dBA for 100 percent of benefitted, first-row receptors.

Noise Abatement Measure Reporting

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.

127.13.8 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, MoDOT will include a note in the public hearing or meeting advertisement indicating that noise barriers are proposed and public comments will be solicited and received at the meeting or hearing. MoDOT also may include a discussion of the noise barrier(s) in the presentation and may provide a dedicated space on the comment card for noise barrier comments. Required invitees for this meeting are all first-row benefitted receptors. Ballots shall be sent via certified mail to all first-row benefitted receptors prior to the public meeting. The ballots may be returned at the public meeting or up to two weeks past the date of the meeting. This practice allows deliberation and the opportunity to ask questions and turn in ballots at the public meeting. A simple majority (51%) of returned ballots is required to qualify a noise wall. 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. The results of the ballot will be reported in the Noise Technical Report.

127.13.9 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).

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; and
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. Also, include the statement that if design changes have occurred and a new noise policy has been approved since the original noise analysis, with FHWA approval the new policy is to be used for the new analysis and final decision. For example: Noise walls are very likely between stations 41+00 and 42+00 and should average 12 ft. in height. 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. If design changes have occurred and a new noise policy has been approved since the original noise analysis, with FHWA approval the new policy is to be used for the new analysis and final decision. If the ballot process for any feasible and reasonable noise abatement has taken place prior to the NEPA documents approval, the results of the ballot will be reported in the NEPA document and the Noise Technical Report.

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 is required by federal law to evaluate noise abatement for new highway construction and widening projects. However, there is no federal requirement for state DOTs to construct noise barriers along existing highways adjacent to developments that are built after highway construction or predate highway noise regulations. Such stand-alone “retrofit” noise barrier projects are referred to as Type II projects. MoDOT does not participate in a Type II noise program.

127.13.10 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 the 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.

127.13.11 Construction Noise

As discussed previously, transportation projects will result in intermittent and temporary noise above existing ambient noise levels due to construction activities. The sound levels resulting from construction activities will be a function of the types of equipment used, the duration of the activities, and the distances between construction activities and nearby land uses.

One key to effectively addressing construction noise effects is proactive communication with the community. Residents and other affected property owners should be notified in advance of construction activities that will generate high noise levels including blasting and pile driving. The following measures shall be incorporated:

  • Inform the public in advance on construction activities that might generate particularly high noise level; and
  • Noise barriers that are included in the design plans should be constructed as early in project construction as practical.

Per 23 CFR 772.19, for all Type I projects, MoDOT is required to do the following:

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; and
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3. Incorporate the needed abatement measures in the plans and specifications.

127.13.12 MoDOT Procedures for Assessment and Abatement of Highway Traffic and Construction Noise

Pursuant to requirements set forth by the Federal Highway Administration (FHWA), EPG 127.13 Noise provides the requirements for the evaluation of highway traffic noise and the consideration of noise abatement when noise impacts are predicted.

The purpose of these noise procedures is to provide detailed technical guidance for conducting highway traffic noise studies for federal, federal-aid and state-funded highway projects in accordance with federal regulations and EPG 127.13 Noise.

MoDOT’s Noise Policy

MoDOT’s noise policy, Policy on Highway Traffic Noise Abatement, was developed in accordance with 23 CFR 772 (July 13, 2010) and FHWA’s Guidance (December 2010). MoDOT’s noise policy was approved by FHWA in May, 2011, and became effective on July 13, 2011. The noise policy was subsequently amended and approved on June 17, 2019. EPG 127.13 Noise (MoDOT’s noise policy) outlines the process that MODOT uses to make decisions on highway traffic noise abatement and to justify the expenditure of public funds in the most cost-effective manner when addressing the total needs of the state’s highway system.

127.13.12.1 Qualifications Necessary to Conduct Noise Studies

Only individuals (MoDOT or consultant staff) qualified in the field of highway traffic noise analysis shall conduct highway traffic noise studies for MoDOT projects or local projects that will utilize federal or state funding.

To be qualified, the person performing the analysis must have 1) demonstrated experience in conducing highway traffic noise analyses for transportation projects in accordance with 23 CFR 772, 2) familiarity with EPG 127.13 Noise , and 3) demonstrated experience conducting noise measurements in accordance with FHWA-PD-96-046, Measurement of Highway-Related Noise, or latest version.

Qualified individuals must have successfully completed the following formal training before conducting work on MoDOT noise studies:

  • Highway Traffic Noise Training and,
  • FHWA TNM 2.5 Course.

MoDOT may request that analysts provide documentation of the above training before or during the conduct of a noise study. MoDOT may also request documentation of other noise studies that the analyst has completed.

127.13.12.2 Noise Study Methodology and Procedures

The primary goal of conducting noise studies is to ensure the information derived and related conclusions are accurate and pertinent to the decision-making process.

To facilitate this goal, noise studies should 1) accurately identify all noise-sensitive land uses that are predicted to be impacted under each Reasonable Build Alternative in the design year, and 2) properly assess the noise abatement measures for impacted land uses listed in EPG 127.13.12.2.6 Evaluation of Noise Abatement Measures.

EPG 127.13.12.2 provides the detailed framework for conducting a highway traffic noise study in Missouri. Noise studies will include the following tasks:

  • Identification of noise-sensitive land uses: Identification of existing land uses in the project area that are sensitive to highway traffic noise, so that the project study area is divided into Noise Study Areas with similar land uses;
  • Determination of existing sound levels: Measurement and/or prediction of existing worst-hour sound levels at noise-sensitive land uses to characterize the existing noise environment in the project area;
  • Determination of future sound levels: Prediction of design year worst-hour sound levels for the No-Build and Reasonable Build Alternatives;
  • Determination of traffic noise impacts: Determination of traffic noise impacts based on the increase in existing sound levels and predicted design year sound levels;
  • Noise abatement evaluation: Evaluation of noise abatement measures for noise-sensitive land uses predicted to be impacted by the project;
  • Discussion of construction noise; and,
  • Provision of information for local officials.

Each of these steps and all analysis results should be thoroughly documented in a Noise Technical Report for the project. Each of these analysis steps is discussed in detail below following a discussion of MoDOT’s criteria for determining noise impacts.

Noise Screening Analysis Procedure

A straight line model design using the FHWA TNM can be used to screen projects that are unlikely to experience noise impacts, such as low volume roadways, projects or project areas that have no receptors, or where abatement most likely would not be feasible. Validation of the straight line model is not required. A straight line model describes a worst-case scenario with higher sound levels than would be expected in detailed modeling and represents a conservative approach to the noise analysis. The straight line model will be prepared as follows for this screening analysis:

  • The model shall use the Existing and the Build Condition traffic information, posted speeds, and Project receiver distances from the roadway to determine noise abatement approach criteria impacts in the Build Condition. It shall also be used to compare the Existing Condition to the Build Condition to determine whether substantial sound level increase impacts of at least a 15 dBA increase are expected.
  • Roadways shall extend at least 500 feet beyond the final receiver(s), perpendicular to the roadway on either side of the project.
  • Any relevant non-traffic noise sources such as rail or airport noise shall be considered and may require measurements.
  • No topography shall be included in the model; only the roadway(s), receiver(s), and traffic information.
  • Project receiver locations must be used. They shall, at a minimum, include receiver location(s) closest to the roadway and receivers placed at 50-foot increments from the roadway to determine the distance from the roadway to which impacts extend. If the closest receptor to centerline is a Category E, then the closest Category B or C receptor within 400 feet of the roadway shall also be examined.

For low-volume roadways, FHWA’s Low Volume Road Noise Calculation Tool (LVRT) can be used to calculate highway traffic noise. A low-volume road is 4000 AADT or less. The LVRT calculates traffic noise using inputs for travel lane characteristics of pavement type and grade percentage; and traffic characteristics of lane average speed and vehicle numbers broken down by percentage of cars, and medium and heavy trucks. The final inputs are the receiver distance from the roadway and the Noise Abatement Criteria (NAC) category. The results of dBA Leq, 1 hour are for the primary lane/receiver side, the opposing lane, and total noise for both lanes.

If the calculated decibel is within 5 dBA of the noise abatement criteria, a detailed noise study is required. The LVRT is automatically set to provide a warning when levels are 5 dBA below the impact criteria.

127.13.12.2.1 Criteria for Determining Impacts

Traffic noise impacts may occur when the predicted noise level at a receptor either approaches or exceeds the Noise Abatement Criteria (NAC) or when there is a substantial increase in noise as a result of the project. Both criteria are defined in EPG 127.13 Noise. MoDOT does not round up results from TNM modeling. A result of 65.6 dB is not rounded up to 66 dB.

The NAC is not arbitrary. The NAC is based upon noise levels associated with interference of speech communication and are a compromise between noise levels that are desirable and those that are achievable. As explained later in this document the NAC should not be viewed as desirable noise levels and they should not be used as design goals for noise barrier construction.

127.13.12.2.2 Identification of Noise-Sensitive Land Uses

Traffic noise analysis shall be performed for 1) developed lands containing noise-sensitive land uses, 2) undeveloped lands where noise-sensitive development is permitted, and 3) to predict future noise levels for undeveloped lands pursuant to 23 CFR 772.17. This identification allows for dividing of the project study areas into Noise Study Areas with similar land uses.

Land uses that are sensitive to highway noise can generally be identified based on review of project plans, aerial photography from web-based mapping sites including Google Maps and Bing Maps, web-based city or county GIS sites, and data from the County Property Assessor.

Even with these mapping resources, a field visit may be advisable so that a sensitive land use is not missed causing delays later when impacts and abatement need to be checked in design.

The municipal planning or codes department also should be contacted to determine if any building permits have been issued in the project area.

Developed Lands

Developed lands that are identified and included in the noise study comprise Activity Categories A, B, C and E land uses with exterior areas of frequent human use, as well as qualifying Activity Category D uses.

If, in MoDOT’s opinion, a land use within the project limits is worthy of consideration as a Activity Category A land use, MoDOT will prepare and submit a “Proposal for Justification for Designating Land Use as Activity Category A” to the FHWA Division Office.

Activity Categories B, C and E land uses are assessed to identify any areas of frequent human use. A frequent human use area is one that is used on a regular basis. Frequent human use areas should be assessed for noise impacts.

Activity Categories B, C and E frequent human use areas could include exterior sitting or eating areas, playgrounds, pools or other similar locations where people may gather. Parking lots and sidewalks are not considered to be noise sensitive areas.

For campgrounds, frequent human use areas might include dedicated camp sites or picnic areas. For cemeteries, frequent human use areas might include exterior areas where services are held on a regular basis but would generally not include individual grave sites.

If an Activity Category C land use has both exterior and interior areas of frequent human use, the exterior area is analyzed for impact as Activity Category C. If there are no exterior areas of frequent human use, or the exterior area is far from or physically shielded from the roadway in a manner that prevents an impact on the exterior areas, then the interior area should be analyzed for impact as Activity Category D.

If there is uncertainty regarding whether an area qualifies as a frequent human use area, MoDOT’s noise specialist is consulted before conducting the noise study.

Permitted Development

Development is deemed to be “permitted” if there is a definite commitment to develop land with an approved specific design as evidenced by the issuance of a building permit.

The noise study should include lands for which development is “permitted” at the date of public knowledge for the project. The date of public knowledge is the date that a project’s final environmental document (i.e. CE, FONSI, or ROD) is approved by FHWA. Or the project is determined by MoDOT to meet the criteria of MoDOT and FHWA’s programmatic CE agreement.

Undeveloped Lands Activity Category G land uses are undeveloped lands that should be addressed as part of the “Information for Local Officials” described in these procedures. Lands used for agriculture that are included in Activity Category F also should be addressed in “Information for Local Officials” section.

127.13.12.2.3 Determination of Existing Noise Levels

The determination of existing noise levels are made using field measurement of actual sound levels and/or the prediction of existing sound levels.

Existing noise levels should be determined using one of the following methods:

  • Method 1: Measurement of Existing Noise Levels
  • Method 2: Prediction of Existing Noise Levels
  • Method 3: Measurement and Prediction of Existing Noise Levels (including validation)

The method selected for each project should consider several factors including: the type of project (i.e. widening or new alignment); facility type; the extent, level of detail, and accuracy of the data available to complete noise modeling for existing conditions; the number of expected impacts; the potential need for evaluation of noise abatement measures; and the effect on the decision-making process. MoDOT’s noise specialist should be consulted to determine the proper method to be used for each project.

127.13.12.2.3.1 Method 1: Measurement of Existing Noise Levels

This method is used for Type I projects involving the construction of a roadway on a new alignment. This method also should be used on Type I projects when the extent, level of detail, and/or accuracy of data for existing conditions is not sufficient to support the development of an accurate noise model for existing conditions.

All measurements should be conducted in accordance with the detailed procedures outlined later in EPG 127.13.12.2.3 Determination of Existing Noise Levels. Use of these procedures will ensure that the existing worst-hour noise levels at noise-sensitive receptors in the project area are accurately determined and reported.

127.13.12.2.3.2 Method 2: Prediction of Existing Noise Levels

This method could be used for projects located in areas where the existing noise environment is dominated by traffic noise from an existing highway, arterial or local road; and where the number of impacts is expected to be low or the impacts will be isolated. This method should not be used for projects involving interstate facilities or similar major highways.

If MoDOT determines that TNM modeling of existing conditions is necessary, then the modeling procedures outlined in Determination of Design Year Sound Levels should be used.

127.13.12.2.3.3 Method 3: Measurement and Prediction of Existing Noise Levels (including validation)

There may be some projects for which both noise measurements and modeling of existing conditions may be needed to facilitate validation of the TNM model. These projects might include large or controversial widening projects; projects where there is uncertainty as to whether impacts will occur; and projects that are likely to include reasonable and feasible noise abatement measures.

127.13.12.2.3.4 Noise Measurements

Noise measurements for any of the methods should be conducted in accordance with FHWA-PD-96-046, Measurement of Highway-Related Noise and using the procedures described below.  

Noise Measurement Locations

Measurement sites commonly include exterior areas of Activity Categories B, C and E land uses.

Noise measurement sites should be selected according to the purpose of the measurement and should be representative of the area of interest, meaning that the sound level at a measurement location is representative of that location and any nearby locations. The site selected is that which is exposed to the highest levels generated by the project. All sites should be representative of areas of frequent human use.

Measurement sites are to be clear of obstructions and the microphone should be located at least 10 feet (3 meters) from any reflective surfaces. Sites should be free of contamination by sources such as barking dogs, HVAC noise, etc.

Interior measurements are generally not needed and would be made only in situations where there are no exterior areas of frequent human use. MoDOT’s noise specialist should be consulted before interior noise measurements are conducted for any project.

Noise Measurement Data Sheets

A noise measurement data sheet must be completed for each measurement location. Copies of the noise measurement data sheets should be provided in the appendix of the Noise Technical Report.

Each noise measurement data sheet is to provide a detailed site sketch including appropriate distance measurements. Photos or video are options to document the site. As well as sound recordings to identify anomalous noises.

The following information should be noted as applicable:

  • Microphone height
  • The roadway elevation relative to the elevation of the measurement location (i.e. in cut, on fill, at-grade)
  • An indication whether the road is on a grade or at-grade
  • Type of intervening ground
  • Any surfaces or areas that could affect sound levels such as ponds, lakes, and parking areas
  • Existing structures including residences, garages, barns, commercial and industrial buildings, noise barriers and fences
  • Significant existing terrain features such as the berms, crests of hills, and drainage ditches
  • Locations and density of areas of trees and/or vegetation
  • A description of any non-traffic noise sources including aircraft and/or train operations, commercial and industrial activities, etc.
  • Calibration results
  • Wind speed and direction
  • Temperature

Consultants conducting measurements should obtain a measurement explanation letter from MoDOT before conducting any field work. This letter will explain the purpose of the measurements and should be provided to residents, business owners, law enforcement, etc., who inquire about the purpose of the measurements.

Equipment

An ANSI Type I or II sound level meter using slow time weighting should be calibrated at the beginning and end of each measurement and the results noted on the noise measurement data sheet.

A windscreen is required and should be of a type specified by the microphone manufacturer as suitable for the particular microphone.

Noise Measurement Times

Sound levels will vary by location and time of day depending on the proximity of noise-sensitive land uses to roads and other background noise sources. Additionally, sound levels can vary with changes in meteorological conditions including shifts in wind speed and direction, and changes in the vertical temperature profile.

Although long-term measurements would more fully characterize the existing noise environment, collection of long-term data at many sites requires significant time, effort and cost. In most cases, the additional data would not significantly change the conclusions regarding the number and locations of noise impacts and the associated need to consider noise abatement.

As a result, a combination of long-term and short-term noise measurements should be conducted to aid in characterizing the existing noise environment in the project area.

127.13.12.2.3.5 Long-Term Measurements

Existing sound levels should preferably be representative of the worst noise hour. The highest traffic volume at the highest average speed usually creates the noisiest conditions. The peak traffic hour may be the worst noise hour if traffic is free-flowing, but typically the worst noise hour will be the hour before or the hour after the peak hour. In most cases, the worst noise hour will occur between 6:00 am and 7:00 pm.

One or more long-term measurements (8 to 14 hours) should be conducted to identify changes in sound levels throughout the day and to aid in identifying the worst noise hour. Long-term measurements include the morning and/or afternoon peak periods.

The noise environment at long–term measurement sites should be dominated by traffic noise from the study roadway. Long-term sites should be isolated from local roadway traffic noise sources and other sources of potential contamination.

The long-term monitor does not have to be attended during the entire course of the measurement. However, it is recommended that field staff return to the monitor site several times during the measurement period(s) to ensure that the sound level meter continues to function properly.

The number of long-term measurements will depend on the number of alternatives and the variation in sound levels throughout the day. Long-term measurements are generally not needed to establish background noise levels in areas where no significant traffic noise sources exist, such as near new roadway alignments in rural areas. Short-term measurements can generally be used to establish background sound levels in these areas.

The long-term measurement data should be recorded in one minute intervals to allow for removal of non-representative, intrusive events. After the measurement is conducted, the data should be thoroughly reviewed to ensure that the reported data is representative of traffic noise levels. One-minute periods where it is clear that recorded sound levels were influenced by random non-traffic noise sources (i.e. intermittent lawn equipment, sirens, other modal noise sources, etc.) should be eliminated.

The long-term measurement data should be used to calculate sound levels for each hour of the long-term measurement period, and to identify the worst noise hour. The long-term data also should be used to develop adjustments to apply to the short-term measurements to arrive at existing worst-hour sound levels at the short-term measurement sites.

127.13.12.2.3.6 Short-Term Measurements

Short-term measurements should be conducted during the long-term measurements at times when traffic is relatively free-flowing. Enough short-term measurements need to be taken to gain a consistent noise reading. The short-term measurements should be adjusted to represent worst-hour noise levels during the measurement period as described above. Short-term measurement data should be recorded in one minute intervals to allow for removal of non-representative, intrusive events.

The duration of the short-term measurement will depend on the density of traffic on the study roadway. Noise measurements near high volume roads can be of shorter duration than measurements near low volume roads. General guidance for determining the minimum duration of short-term measurements is provided in Table 127.13.12.2.3.6.  

Table 127.13.12.2.3.6, Short-Term Measurement Durations
Traffic Volume (vehicle/hour/lane) Minimum Duration (minutes)
High (>1000) 15
Medium (500-1000) 20
Low (<500) 30
Meteorological Conditions
Meteorological conditions can affect sound levels and sound propagation, particularly at long distances.
Measurements should not be conducted when the wind speed(s) at the microphone exceeds 12 mph (5 m/s), regardless of wind direction. Wind speed should be monitored and reported on the noise measurement data sheet.
There is no set limit on temperature during noise measurements. However, the ambient temperature must be noted on the noise measurement data sheet.
Pavement Conditions
Noise measurements should be conducted only when road surfaces are dry. Road surfaces also should be free of extraneous material such as gravel.
Data Analysis
The measured sound level data should be imported into spreadsheet tables and any measurement intervals that are contaminated due to unrepresentative noise sources, high wind, or other factors should be eliminated. A note should be made of the minutes of unrepresentative noise sources that occurred in a measurement period. If it is several minutes this may cause the measurement period to be less than the recommended amount.

127.13.12.2.4 Determination of Design Year Sound Levels

127.13.12.2.4.1 No-Build Alternative

For most projects, sound levels for the No-Build Alternative in the design year should be predicted by evaluating existing and design year traffic volumes on the roadway network. Background sound levels in areas that are not affected by highway traffic noise should generally not be increased.

The increase in sound level from the existing year to the design year can be estimated using the following equation:

Increase in sound level = 10 log (1+N/10)
Where,
N = Percent increase in traffic between existing and design year

For example, doubling the traffic on a roadway would result in a 3 dB increase in the sound level at a given receptor assuming all other conditions remain the same. Similarly, an increase in existing traffic volumes of 60% would result in an approximate 2 dB increase in sound levels. In this case, design year sound levels would be approximately 2 dB higher than existing sound levels.

The projected No-Build traffic volumes for the design year should be reviewed to determine if the design hour volumes could be accommodated at free-flow traffic conditions. If the projected traffic volumes would result in decreases in travel speeds, the traffic volumes should be analyzed to identify the increase in traffic volume that could be accommodated during the worst noise hour at free-flow traffic conditions.

127.13.12.2.4.2 Build Alternative(s)

Noise modeling of the Reasonable Alternative(s) should be completed using the most recent version of the FHWA Traffic Noise Model (TNM) computer program. The program should be used to calculate design year noise levels at the noise-sensitive land uses in the project area, including the measurement sites.

Based on MoDOT’s experience, detailed and accurate modeling of the Reasonable Alternative(s) in the design year has been found to be the best way to ensure 1) the best estimates of design year sound levels for all receptors, and 2) the most accurate accounting of the impacts resulting from the project.

Detailed instructions on development of a TNM 2.5 model are available.

The TNM model should include the following for all Reasonable Alternatives:

  • The proposed roadway alignment including all existing and proposed ramps and intersections;
  • Local roads that contribute to the noise environment;
  • Receivers;
  • Existing noise barriers or large buildings that act as noise barriers;
  • Terrain features including intervening hills, tops of cuts, and bases of fills;
  • Rows of buildings that provide shielding; and,
  • Intervening ground zones that will affect sound propagation including parking lots and bodies of water.

All TNM runs developed for the project shall be transmitted to MODOT electronically at the time any draft or final report is submitted.  

Mapping
The following mapping should be used in the development of the TNM models as available:
  • Functional plans
  • Cross-sections
  • MicroStation design files, including proposed horizontal alignment and vertical profiles
  • Missouri GIS data
  • County GIS data
  • USGS maps
  • Or other sources, such as 3-D design plans, if available.
TNM Roadways
The proposed roadway alignment including all existing and proposed ramps and intersections must be modeled. Local roads that contribute to the noise environment also must be modeled.
The direction of travel must be properly modeled for each TNM roadway. For multi-lane highways, follow the recommendations contained in FHWA’s Recommended Best Practices for the Use of the FHWA Traffic Noise Model (Final Report, December 8, 2015).
The actual width of the roadway pavement must be modeled including each of the travel lanes and shoulders. Additionally, the outside edge of pavement must be modeled as close as possible to the actual location.
All appropriate flow devices including on-ramps, stop signs, traffic signals, and toll booths must be modeled.
Traffic
Design year sound levels should be predicted for the worst-noise hour, which would normally occur when the highest traffic volume can travel at the highest possible speed.
Traffic projections for the design year can be obtained from MoDOT’s Transportation Planning Division. These traffic projections will be used to develop a design year worst noise hour. Existing hourly traffic volumes can be obtained from MoDOT’s Transportation Management System (TMS) upon request. Existing hourly volumes may be used to determine future hourly volumes. These Design Hour Volumes (DHVs) must be used for the noise analysis since they represent the highest number of vehicles expected to travel on the roadway network in a given hour.
The DHVs must be modeled at the planned posted speed for the Reasonable Alternative(s) since modeling DHVs at posted speeds provides a conservative estimate of worst-hour noise levels.
Traffic projections for the project also must include truck projections. If the percentage of trucks for the design hour is not provided, then the percentage of trucks during the design hour must be assumed to be two-thirds of the projected percentage of trucks on a daily basis. The split between medium trucks and heavy trucks must be based on traffic classification counts if they are available. If classification counts are not available, a split must be requested from MoDOT’s Transportation Planning Division.
The Noise Technical Report must include a table summarizing the projected traffic volumes for each modeled TNM roadway. The traffic projections must be included in an appendix of the Noise Technical Report.
TNM Receivers
Traffic noise analysis must be performed for Activity Categories B, C and E land uses with areas of frequent human use as well as for FHWA-approved Activity Category A land uses. The analysis also must include qualifying Activity Category D uses and Activity Category G undeveloped land where development is permitted. The land use categories must be grouped accordingly if they are separate from each other.
Receivers must be modeled at all noise measurement sites.
127.13.12.2.4.3 Activity Category B Land Uses

For residences, receivers must be located in areas near the residences where frequent human use would be expected such as patios, decks, balconies, common grounds or areas such as swimming pools, playgrounds, or other appropriate locations.

Receivers must be located in areas of the property that are oriented toward the project roadway. Therefore, receivers may need to be located to represent front porch or front yard locations. Generally, receivers should be located approximately 10 feet from the residence.

Upper story locations such as those at apartments and condominiums and elevated decks must be modeled for the purpose of identifying impacts and counting benefits. If a house has both a porch and elevated deck, choose only one to be modeled as the receiver location. Choose the likeliest loudest location based on roadway elevation. Noise abatement is provided for the receiver location at the roadway elevation, not for upper story locations as discussed in EPG 127.13.12.2.6 Evaluation of Noise Abatement Measures.

A single receiver can represent more than one residential unit as long as the units would be expected to have comparable existing and design year sound levels.

127.13.12.2.4.4 Activity Category C Land Uses

Receivers must be located at frequent human use areas of Activity Category C land uses. Areas of frequent human use must be exposed to traffic noise on a regular basis over the course of a year. These locations might include exterior sitting or eating areas.

For campgrounds, these areas might include dedicated camp sites. For cemeteries, these areas might include exterior areas where services are held on a regular basis but would generally not include individual grave sites.

If an Activity Category C land use has both exterior and interior areas of frequent human use, the exterior area should be analyzed for impact as Activity Category C.

127.13.12.2.4.5 Activity Category D Land Uses

Primary consideration shall be given to exterior areas where frequent human use occurs. 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 is appropriate for use as the basis for determining noise impacts for land uses in Activity Category D.

Receivers should be modeled at exterior areas of these properties facing the highway. After the TNM predictions are made, interior noise levels should be estimated in accordance with FHWA’s guidance. FHWA’s procedure requires that the type of building construction be identified and documented. A determination whether the building would normally operate under “closed windows” conditions must then be made. Generally, the windows shall be considered closed unless there is firm knowledge that the windows are in fact kept open almost every day of the year. The appropriate sound level reduction from Table 127.13.12.2.4.5 for building attenuation must be applied to the predicted exterior noise level to arrive at the predicted interior noise level. This level is compared to the NAC of 52 dB(A)) for Activity Category D land uses to determine if interior impacts are predicted. The number of equivalent receptors is determined by assigning the whole building a value of 1.

Table 127.13.12.2.4.5: Building Noise Reduction Factors
Building Type Window Condition Reduction
All Open* 10 dB
Light Frame Ordinary Sash (closed) 20 dB
Storm Windows 25 dB
Masonry Single Glazed 25 dB
Double Glazed 35 dB
* 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.

Source: FHWA’s Highway Traffic Noise Analysis and Abatement: Policy and Guidance.

There may be situations where it is desirable to develop noise reduction factors through the conduct of additional field measurements or more detailed acoustical analysis. MoDOT’s noise specialist will determine the need for interior measurements on a case-by-case basis.

127.13.12.2.4.6 Activity Category E Land Uses

Receivers should be modeled at exterior frequent human use, such as exterior restaurant seating areas, pools or playgrounds. Areas of frequent human use must be exposed to traffic noise on a regular basis.

Exterior areas of commercial properties including sidewalks and parking areas are not considered to be areas of frequent human use.

Hotels and motels that serve as long-term apartments must be analyzed as Activity Category B.

127.13.12.2.4.7 Number of Receivers

The number of modeled TNM receivers for a project should be adequate to facilitate an accurate count of the number of impacts that will result from each Reasonable Alternative.

For a project with a large number of residences, it is preferred, but not necessary to model every residence. One receiver can represent multiple residences if the location is considered to be acoustically representative of several residences.

If noise barriers are being evaluated, enough receivers should be modeled to ensure an accurate count of the number of benefits.

A table and/or an aerial map exhibit that indicates the number of residences being modeled by each receiver should be included in the Noise Technical Report.

The analyst should exercise judgment in determining the distance at which receivers should be modeled. Consideration should be given to the distance within which impacts are expected, as well as where benefits might occur if noise abatement is evaluated.

For projects involving widening existing roads or interchange modifications, model to the point where impacts are no longer expected. However, the distance within which impacts might occur will often be much greater for projects involving construction of a road on a new alignment.

The analyst should be aware that unique site conditions such as a high percentage of trucks or the existence of intervening “hard“ ground, such as paved areas or bodies of water, also might result in impacts at greater distances that would normally be expected.

127.13.12.2.4.8 Receiver Elevations

Receiver elevations should closely approximate actual ground elevations. The elevation datum should be Mean Sea Level (North American Vertical Datum of 1988 or National Geodetic Vertical Datum of 1929). If a different datum is used, then a discussion of the datum should be included in the Noise Technical Report.

First-floor receivers should generally be modeled 5 feet (1.5 m) above the ground and second-floor receivers should generally be modeled 15 feet (4.5 m) above the ground.

127.13.12.2.4.9 Receiver Names

Generally, receivers should be named by designating the address of the property where the receiver is located. Address information can be obtained from MoDOT District Right of Way or various county GIS websites.

An alternative method of receiver naming is to designate the receiver as first (1), second (2), third (3) or subsequent row relative to the roadway. The relative location is then followed by a hyphen, the first two letters of the local street on which the receiver is located, and the station of the adjacent roadway being modeled. It also helps to include the NAC for that property so that proper grouping of land uses can be ensured. For example, a second-row receiver on Green Street near STA 335+00 would be designated as 2-GR335B.

TNM Barriers
Existing noise barriers or noise barriers that are being evaluated as abatement measures should be modeled, as well as any structures that act like noise barriers such as median barriers, parapet walls and large buildings.
127.13.12.2.4.10 Median Barriers

If the future typical cross section shows that a median barrier will be constructed, the median barrier shall be modeled in TNM at the proposed location(s) and height(s).  

127.13.12.2.4.11 Parapet Walls

Parapet walls should be modeled at the existing or proposed location(s) and height(s) so that the shielding from the parapet wall is included in the no-abatement sound levels.

127.13.12.2.4.12 Buildings

Buildings that cannot be accurately modeled as part of a building row should be modeled as fixed height noise barriers.

127.13.12.2.4.13 Existing Noise Barriers

Solid noise barriers that were constructed to abate noise should be modeled as fixed height noise barriers. See FHWA’s Noise Policy Frequently Asked Questions.

127.13.12.2.4.14 Privacy Fences

Privacy fences that are constructed with materials and in a manner that would be expected to reduce sound levels should be modeled in TNM. These types of fences could include solid cinder block or brick walls.

Wooden privacy fences are not typically constructed to mitigate noise and should not be modeled as noise barriers. However, these fences can provide small reductions in sound levels. If the fence is expected to remain in good condition over the lifetime of the project (i.e. 20 years in the future), then it may be appropriate to model the fence as a TNM building row as described below. However, MoDOT’s noise specialist should be consulted before a privacy fence is modeled.

Field measurements also can assist in evaluating the noise level reduction that might be provided by existing fences.

TNM Building Rows
Multiple small buildings, such as rows of houses that act as multiple small barriers with gaps should be modeled as building rows with a uniform low transmission loss.
TNM Terrain Lines
TNM terrain lines should be used to define the terrain between TNM roadways and receivers. TNM terrain lines should be modeled where they break the line-of-sight or where they would reduce excess ground attenuation. TNM terrain lines could include:
  • The top of cut for a depressed roadway
  • The bottom of deep drainage ditches
  • The edge of fill for roadways on fill
  • Ridges of intervening hills
  • Lines of constant elevation of an intervening hill.
TNM Ground Zones
A Lawn should generally be specified as the default ground type for MoDOT projects. Any large areas of ground type that would be expected to affect sound propagation should be modeled as TNM ground zones. Ground zones might include parking lots and lakes.
TNM Tree Zones
Tree zones should not be modeled on MoDOT projects unless they meet FHWA’s definition which states that tree zones should consist of long, wide regions of heavy, non-deciduous woods and undergrowth, not just individual trees or several rows of trees. The vegetation also must be sufficiently dense to completely block the view along the sound propagation path. This requires dense undergrowth as well as dense tree-top foliage. Tree zones should not be modeled unless they have this vegetative density and not without MoDOT’s noise specialist’s concurrence.
TNM Contours
This TNM feature should only be used for land-use planning activities. This feature should be used for Activity Category G, undeveloped lands, that are not permitted for development, to inform local officials in an effort to prevent future noise impacts on these lands.
TNM Model Validation
MoDOT’s standard procedure for validation is the comparison of existing noise levels and predicted noise levels for the existing traffic condition. Models are considered validated if measured and predicted noise levels are within +/- 3 dB (A).
For TNM model validation against existing measured data, attention should be paid to all existing conditions (including pavement type); to assure that the modeling input parameters are consistent with what actually exists. If the existing pavement is concrete, for validation purposes only, set the pavement type accordingly. Once validated, the pavement type must be changed back to AVERAGE pavement for all other models to account for changes of pavement type over time.
Review of Design Year Sound Levels
The predicted design year sound levels for the Reasonable Alternative(s) should be thoroughly reviewed to assess whether the predicted sound levels at each receiver are reasonable given the analyst’s knowledge and understanding of the source of the traffic noise, the path between the source and the receiver, and the characteristics of the intervening terrain.
The predicted design year sound levels at the measurement locations should be compared to the existing and design year no-build worst-hour sound levels at each measurement location to assess whether the predicted change in sound level due to the project is reasonable.
If the predicted change in noise levels due to a project is significantly higher or lower than the change that the analyst would expect, then the analyst should thoroughly review the modeling for the Build Alternative to ensure that the TNM model accurately represents the design year conditions. For example, a predicted 6 dB increase in the sound level would not be expected if the traffic did not double and the roadway did not move closer to the receiver.

127.13.12.2.5 Determination of Traffic Noise Impacts

Traffic noise impacts for each Reasonable Alternative(s) should be identified in accordance with EPG 127.13 Noise. An impact analysis should be included for the No-Build Alternative.

Each modeled receiver should be identified as not impacted, impacted based on the NAC, impacted based on substantial increase in sound levels, or impacted based on both the NAC and a substantial increase in sound levels. The information should be presented in a table in the Noise Technical Report.

The total number of impacts by Activity Category resulting from each Reasonable Alternative(s) should be determined and summarized in a table in the Noise Technical Report. MoDOT does not round TNM noise impact results. If TNM calculates a result of 65.9 dBA it is not rounded up to 66.0.

If traffic noise impacts are not predicted for the Reasonable Alternative(s) in the design year, the analysis is considered complete and noise abatement measures should not be evaluated. This does not include the No-Build alternative, which is not considered a Reasonable Alternative. This determination should be stated in the Noise Technical Report.

127.13.12.2.6 Evaluation of Noise Abatement Measures

Noise abatement is evaluated when noise impacts are predicted in the design year for the Preferred Alternative. At a minimum, MoDOT will consider noise abatement in the form of a noise barrier, since barriers are generally the best available abatement measure to reduce sound levels for impacted land uses.

127.13.12.2.7 Noise Barrier Design

Noise barriers are evaluated using TNM to reduce sound levels to achieve MoDOT’s noise reduction design goal at impacted land uses. MoDOT’s barrier design philosophy requires an attempt at achieving benefits of a minimum of 7 dBA reduction at 100% of first-row, first-story benefitted receivers. All benefitted receivers (including any upper-level receivers, if applicable) are still considered in cost effectiveness calculations from the proposed barrier design. MoDOT does not round TNM noise reduction results. If TNM calculates a reduction of 6.9 dBA it is not rounded up to 7.0.

First-row receptors are noise-sensitive land uses that face the project roadways without substantial visual occlusion from traffic noise. Additionally, receptor parcels are required to abut the roadway right-of-way to be considered first-row. Receptors with developable intervening parcel(s) separating the receptor parcel from the abutting roadway right-of-way are considered second row or greater receptors.

Barrier Location
Acoustically, the most effective noise barriers are generally located close to the source (i.e. at the highway shoulder) or close to the receptor (i.e. at/near the right-of-way). The analyst should exercise judgment in determining the most effective location for a barrier. Additionally, in areas where a road transitions from cut to fill and vice versa, the barrier will likely need to transition from a location near the road to a location near the right-of-way.
Some situations may require an analysis of more than one barrier location and may require coordination with MoDOT’s noise specialist.
Barrier Heights
Barrier heights will vary considerably depending on traffic volumes and mixes, the characteristics of the intervening ground, and the location of the road relative to the impacted receptors (i.e. cut or fill). When designing walls, MoDOT’s policy of limiting heights to 20 feet due to wind load must be accounted for by the designer.

127.13.12.2.8 Noise Barrier Feasibility and Reasonableness

A preliminary qualitative assessment for feasibility should be completed to identify any major design, construction, maintenance or safety factors associated with construction of noise barriers. The factors that should be evaluated include:

  • Access to adjacent properties for non-access controlled facilities
  • Sight distance
  • Clear zone
  • Drainage
  • Utilities
  • Constructability of the barrier including issues associated with constructing noise barriers on bridges

The extent to which these issues can be assessed will depend on the project development process. The Noise Technical Report and NEPA document should indicate the type of plans upon which the noise study was based.

Noise barriers will generally be determined feasible for potential non-acoustic (e.g., engineering) reasons during the NEPA process. Non-acoustic issues that could affect the feasibility determination during the final design process should be discussed in the Noise Technical Report and NEPA document.

MoDOT will assess all potential feasibility issues during the final design process for those barriers that are determined to be acoustically feasible and reasonable. Issues associated with drainage, sight distance, clear zone and utilities can generally be addressed during the final design process without affecting the feasibility and reasonableness of the noise barrier.

The feasibility of providing noise abatement may be influenced by other significant noise sources in the areas including rail, aircraft, and industrial/manufacturing operations. The extent to which other significant noise sources affect acoustic feasibility will depend on the temporal nature of the noise source as well as the sound levels themselves. In these cases, a more detailed assessment of acoustical feasibility may be needed and MoDOT should be consulted.

Feasibility alone does not dictate whether a noise barrier will be built. Each noise barrier also must be “reasonable” in accordance with EPG 127.13 Noise.

As stated in EPG 127.13 Noise, abatement will only be assessed where noise impacts are predicted and where frequent human use occurs. Primary consideration will be given to exterior areas.

Activity Categories C, D and E Land Uses
The reasonableness determination of benefitted receptors for Activity Categories C, D and E land uses is a residential equivalent frontage-based method. An equivalent number of residences are based on the feet of frontage where frequent human use occurs for Activity Categories C, D and E. The average of the residential frontages in the project area (e.g. one receptor equals 100 ft.) is divided into the frontage of the property being analyzed to determine the number of equivalent receptors. For modeling purposes the receptor will be placed at the location where the human activity occurs. That number will then be multiplied times the allowable 1300 square feet per benefitted receptor and used in the barrier analysis to assess the cost-benefit reasonableness criteria.

127.13.12.2.9 Views of Benefited Property Owners and Residents

Per EPG 127.13 Noise, the ballots of benefited property owners and residents will be used to make the final noise abatement decisions. This input will be conducted in some cases at the NEPA CE2 stage, but more likely at the design stage. Ballots will be received by mail or at public meetings or hearings.

MoDOT will include a note in the public hearing or meeting advertisement indicating that noise barriers are proposed and public comments will be solicited and received at the meeting or hearing. MoDOT also may include a discussion of the noise barrier(s) in the presentation and may provide a dedicated space on the comment card for noise barrier comments. Required invitees for this meeting are all benefitted receptors. Ballots shall be sent via certified mail to all benefitted receptors, preferably two weeks 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 (51%) of returned ballots is required for property owner and resident approval. No other voting opportunities will be given. The viewpoints of non-owner residents (tenants) 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. Information at the meeting should outline why and when noise levels are studied, how sound is measured and what are the possible abatement measures; the criteria for qualifying for noise abatement; the areas being reviewed and who are the eligible potentially benefitted receivers; and what is the process for moving forward. See the attached example presentation that covers all the main points for the public meeting. It is beneficial to provide this information on your project web page. Many stakeholders will be interested in how the noise wall policy works, not just those directly benefitting.

The Noise Technical Report will document the process of obtaining the views of benefitted property owners and residents and any correspondence sent and received.

127.13.12.2.10 Assessment of Construction Noise

Construction noise related to transportation projects is addressed in the Noise Technical Report and in the environmental document for the project. In most cases, construction noise may be adequately addressed through a project-specific narrative discussion.

The sound levels resulting from construction activities will be a function of the types of equipment used, the duration of the activities, and the distances between construction activities and nearby land uses.

One key to effectively addressing construction noise effects is proactive communication with the community. Residents and other affected property owners should be notified in advance of construction activities that will generate high noise levels including blasting and pile driving. The following measures should be incorporated:

  • Inform the public in advance on construction activities that might generate particularly high noise level; and
  • Noise barriers that are included in the design plans should be constructed as early in project construction as practical.

Per 23 CFR 772.19, for all Type I projects, MoDOT is required to do the following:

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; and
3. Incorporate the needed abatement measures in the plans and specifications.

Local noise ordinances are covered in Section 107.1, Laws to be Observed, of Missouri Standard Specifications for Highway Construction. The contractor shall know, observe and comply with all federal and state laws, local laws, codes, ordinances, orders, decrees and regulations existing at the time of or enacted subsequent to the execution of the contract that in any manner affect the prosecution of the work, except as specified in the contract or as directed by the engineer. The Contractor shall also ensure that any subcontractor know, observe and comply with all federal and state laws, local laws, codes, ordinances, orders, decrees and regulations as outlined above.

127.13.12.2.11 Information for Local Officials

Noise predictions from the Noise Technical Report are provided to local officials so it can be used to help minimize future traffic noise impacts on currently undeveloped lands within the present Type I project. Noise predictions must be included in the “Information for Local Officials” section of the Noise Technical Report and NEPA document. The MoDOT district office will provide the appropriate local officials where the Type I project is located both the preliminary noise analysis information in the NEPA document and the Final Noise Technical Report.

Information on Noise Compatible Planning Concepts
MODOT encourages local governments with jurisdiction over undeveloped lands, as well as potential developers of these lands, to practice noise compatibility planning to avoid future noise impacts.
The Noise Technical Report should include references to the following FHWA guidance documents on noise compatible land use planning:
Estimates of Design Year Noise Levels
The Noise Technical Report and environmental document should include a brief discussion of the location and type of undeveloped lands in the project area.
TNM should be used to predict design year sound levels that approach the NAC from the proposed edge of the nearest travel lane for these undeveloped areas.
The predicted sound levels should be summarized in a table or shown on an aerial and the Noise Technical Report should clearly state the following:
“The noise predictions do not represent predicted levels at every location at a particular distance back from the roadway. Sound levels will vary with changes in terrain and will be affected by the shielding of objects such as buildings. This information is being included to make local officials and planners aware of anticipated highway noise levels so that future development will be compatible with these levels.”

127.13.12.3 Noise Technical Report

The results of the noise analysis should be documented in a Noise Technical Report that should have a logical sequence and language that adequately describes the procedures used to complete the noise analysis. Tables and figures should be used to convey the study results and make the report easily understandable by both a technical reviewer and a lay person. MoDOT will use this report to document adherence to highway traffic noise regulations. Therefore, the recommendations and findings will be approved by MoDOT after going through a review of a draft and final report. The report will be final when public outreach, ballot count, and noise abatement decision have been finalized. A re-evaluation of a barrier design that causes a change will be documented in the existing report at either the draft or final stage.

The Noise Technical Report should generally contain the following sections:

1.0 Executive Summary
2.0 Project Description
3.0 Criteria for Determining Impacts
3.1 Traffic Noise Terminology
3.2 Noise Abatement Criteria (NAC)
4.0 Identification of Noise-Sensitive Land Uses and Noise Study Areas
5.0 Determination of Existing Sound Levels
6.0 Determination of Future Sound Levels
6.1 No-Build Alternative
6.2 Build Alternative (s)
7.0 Impact Determination Analysis, Build Alternative(s)
8.0 Noise Abatement Evaluation
8.1 Noise Barrier Feasibility
8.2 Noise Barrier Reasonableness
8.3 Ballot Results of Benefited Property Owners and Residents
8.4 Summary
9.0 Construction Noise
10.0 Information for Local Officials
11.0 Indirect and Cumulative Effects
12.0 References

Appendices (as applicable):

Typical Cross-Sections
Noise Measurement Data Sheets and Photographs
Traffic Projections
TNM Plan Views
Design Year Sound Levels and Impacts, Build Alternative(s)
Development Data Analysis
Noise Barrier Analysis Results

The state project number should be included on the report cover.

All TNM runs developed for the project should be transmitted to MoDOT electronically at the time any draft or final report is submitted. MoDOT’s noise specialist and district project manager will be responsible for review and approval of the report and its conclusions.

127.13.12.4 Noise Section of Environmental Document

The environmental document for the project should include a discussion of the process to conduct the noise study and the findings. The environmental document for the project also should include brief discussions of the public involvement process.

127.13.12.5 Final Noise Abatement Decisions

Conditions can change during the project design process. These changes may affect the preliminary noise abatement determinations in the environmental document. Such changes could include modifications to the proposed cross-sections, shifting the alignment, and changing roadway or ramp grades.

Final decisions regarding the construction of noise barriers are made during the final design process. If design changes have occurred and a new noise policy has been approved since the original noise analysis, with FHWA approval the new policy is to be used for the new analysis and final decision.

127.13.12.6 Final Noise Barrier Design

Preliminary noise barrier designs will be developed once right-of-way plans have been completed. The preliminary barrier designs will be incorporated into the preliminary roadway design plans. The final noise barrier design will be revisited when the preliminary roadway design plans are completed. The Noise Technical Report will be amended to record any changes from original barrier design as a result of a new analysis.

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