7.0 MITIGATION OF CONSTRUCTION NOISE

7.1 Introduction

This chapter provides more examples of typical mitigation techniques and options. Information provided is not to be considered all-inclusive, nor is it intended to limit the ingenuity or resourcefulness of designers, contractors, and inspectors, or create a strategy uniquely suited to the characteristics of a specific project.

The level of detail in a contract required to address construction noise mitigation is dependant on the complexity of the project, the amount and type of work required, and the sensitivity of the area beyond the project boundary. Therefore, not all projects require the same amount of detail. Such detail could range anywhere from the inclusion of a standard specification requiring the contractor to be governed by local noise ordinances, to realigning the highway, providing for abatement structures, and/or relocation of residents. The effective control of highway construction noise can be achieved in much the same manner as the control of operational traffic by considering the following techniques: • Alternative design options; • Mitigation at the source; • Mitigation along the path; and • Mitigation at the receiver. Another effective technique is the inclusion of operational conditions via contract specifications and special provisions. Public involvement and project coordination are also an essential components of the overall mitigation strategy worthy of consideration during all phases of a project. For a more detailed discussion of this topic, refer to Chapter 8. Most of the options presented in this chapter can be employed independently or in combination, depending on the scope of the project and the resultant effects that are desired. While reductions in noise levels will vary with the method employed, consideration of all practical and feasible options is essential during all stages of the project development from planning, through design and construction, to final evaluation.

Table 7.1. Overview of mitigation options. Design Options    Design and Project Layout    Sequence of Operations    Alternative Construction Methods Contract Specifications/Special Provisions    Operational Constraints    Time Periods and Duration    Specified Equipment    Noise-Related Incentives/Disincentives    Training Programs for Contractor Mitigation at the Source    Stationary Equipment    Mobile Equipment    Selection of Equipment    Inspection/Maintenance Programs    Equipment Operation Training Mitigation Along the Path    Natural Shielding    Temporary Shielding    Permanent Shielding Mitigation at the Receiver    Building Envelope Improvements    Masking    Relocation of Residents Public Involvement and Project Coordination    Critical components of the overall mitigation strategy.    Should be considered during all phases of a project.

7.2 Design Options

Noise impacts can occur on any project involving the construction of a highway facility. While the magnitude of the impact construction noise may have on a community may not be known early in the project development stages, measures can be implemented during the design phase that can help to reduce the anticipated noise impacts at sensitive receptors. However, design changes and modification to project layout are not always practical or feasible. Also, the magnitude of the noise reduction attained from some of these techniques is usually difficult to determine prior to and possibly even during construction.

7.2.1 Design Phases.
In addressing construction noise mitigation during the design phases of a project, abatement opportunities can be considered for a variety of areas and features including those listed below:

• Storage Areas: During the planning and design stages of a project, storage areas may be able to be designated in locations removed from sensitive receptors. Where this is not possible, the storage of waste materials, earth, and other supplies may be able to be positioned in a manner that will function as a noise barrier.

Figure 7.1. Storage area in highway right-of-way. (Photo #177)

Figure 7.2. Partial shielding of storage area in residential area. (Photo #247)	Figure 7.3. Storage area in remote location. (Photo #1257)

• Haul Roads: Haul roads can be designated in locations where the noise impacts caused by truck traffic will be reduced.

Figure 7.4. Designated haul routes. (Photo #560)

• Detours: Increased noise generated by temporarily rerouting traffic during construction is considered as part of construction noise. It is essential to consider efforts to reduce the impact from such changes during the design phases of the project.

Figure 7.5. Shifting of traffic to accommodate construction. (Photo #1261)

• Existing Barriers: As early as possible in the design development process, natural and artificial barriers such as ground elevation changes, existing buildings, noise walls, and other structures can be considered for use as a noise shield during certain operations.

Figure 7.6. Existing retaining wall acting as noise barrier during construction. (Photo #543)

7.2.2. Sequence of Operation.
The sequencing and scheduling of construction operations is equally important in addressing and mitigating construction-related noise

• Concurrent Operations: It may be possible to schedule several noisy operations concurrently to take advantage of the fact the combined noise levels produced may not be significantly greater than the level produced if the operations were performed separately.

• Early Construction of Noise Barriers: Ultimately, noise barriers that are to be constructed as part of the project for traffic noise abatement can possibly be installed during the initial stages of construction to reduce the noise impacts of the construction.

Figure 7.7. Early construction of noise barriers. (Photo #447)

7.2.3 Alternative Construction Methods.
Alternatives to standard construction techniques may also be available and determined to be more practical and/or cost-effective in dealing with construction noise impacts and perceptions. Examples associated with several operations are discussed below.

• Pile Driving: Pile driving may produce noise levels in excess of acceptable limits, even when feasible noise reduction methods are used. Various dampening and shielding methods discussed later can attain some reduction. However, such methods rarely reduce the noise level to an acceptable level for the sensitive receptors close to the site. As an alternative to driving piles, it is possible to use vibration or hydraulic insertion techniques. Drilled or augured holes for cast-in-place piles are another alternative that may produce noise levels significantly lower than the traditional driving method.

Figure 7.8. Alternative to pile driving. (Photo #509)

• Compressors: While most compressors are powered by diesel or gasoline engines, many are contained or have baffles to help abate noise levels. Electric compressors are significantly quieter than diesel or gasoline engine powered compressors.

Figure 7.9. Diesel compressor with baffled housing. (Photo #69)

7.3 Contract Specifications and Special Provisions

Contract specifications and special provisions are typically produced during the design stages of project development and may be included in the project plans and contract documents. Ideally, use of these documents is considered in conjunction with other control methods to achieve an overall construction noise strategy. Examples of such specifications ref. 023, ref. 028, ref. 103, and ref. 053 are referenced in this Handbook.

7.3.1 Construction Noise Criteria Limits.
When establishing suitable noise criteria limits for specifications and special provisions, they can be characterized as either being “relative” or “absolute” or a combination both. These can be defined even further by dividing the set limits into specific time periods during the day such as daytime, evening and nighttime. Experience has shown that the “absolute” criteria combined with the “relative” criteria levels appears to be more realistic and tends to be self-adjusting to varying conditions, particularly when defined for the various periods of the day. An example of one such set of construction noise criteria is shown in Table 7.1.

Table 7.2. Example of Absolute and Relative Construction Noise Criteria Limits

Lot-Line Construction Noise Criteria Limits A-weighted in dB, RMS slow
Noise Receptor Locations and Land-Uses	Daytime (7 AM - 6 PM)		Evening (6 PM - 10 PM)		Nighttime (10 PM - 7 AM)
	L10	Lmax	L10	Lmax	L10	Lmax
Noise Sensitive Locations: Residences, Institutions, Hotels, etc.	75 or Baseline + 5 (whichever is louder)	85 90 (impact)	Baseline + 5	85	Baseline +5 (if Baseline <70) Baseline +3 (if Baseline >70)	80
Commercial Areas: Businesses, Offices, Stores, etc.	80 or Baseline + 5 (whichever is louder)	None	None	None	None	None
Industrial Areas Areas: Factories, Plants, etc.	85 or Baseline + 5 (whichever is louder)	None	None	None	None	None
L10 noise compliance readings are averaged over 20 minute intervals. Lmax noise compliance readings can occur instantaneously. Baseline noise conditions must be measured and established prior to construction work, commencing in accordance with the noise specification, which requires baseline noise readings over three 24-hour periods at each receptor lot-line location.
Source: Adapted from Central Artery/Tunnel Noise Specification and Table 2 in Appendix A.

As shown in Table 7.2, the noise specification’s lot-line criterion is primarily a relative criterion in which construction noise levels, in general, can not exceed baseline (preconstruction) L10 noise levels by more than 5 dB at identified noise sensitive receptor locations. L_max noise limits also apply at the lot lines and are intended to address loud impact-type noise events. In the above criteria, the following three types of receptor land uses have been suggested:

• Noise Sensitive Areas consisting of sites with nighttime land use such as residences, hotels, and hospitals;
• Commercial Areas containing land uses such as businesses and office buildings; and
• Industrial Areas containing factories and large plants.

7.3.2 Time Periods and Duration.
Time constraints and use of equipment regulations can be very effective in reducing the impacts caused during sensitive time periods. In addition, operating noisy equipment only when necessary and switching off such equipment when not in use can minimize noise impacts.

Figure 7.10. Nighttime bridge construction. (Photo #661)

Figure 7.11. Nighttime demolition operation. (Photo #1049)

7.3.3 Specified Equipment.
Another effective noise mitigation technique involves use of the quietest practical type of equipment. To avoid confusion and misinterpretations, such types should be specified in the contract specifications and special provisions.

7.3.4 Noise Related Incentives/Disincentives.
Another technique worthy of consideration involves the inclusion of incentives and/or disincentives in the contract specifications to encourage the contractors to participate in the mitigation program and to make them more accountable for impacts.

7.3.5 Training Programs for Contractors.
It may be appropriate to require contractors to participate in training programs related to project-specific noise requirements, specifications, and/or equipment operations. Such training may be provided by agency or project management personnel, outside consultants, and/or equipment manufacturers or suppliers. For example, project personnel (or consultants assigned to the project) may train the contractor on the measurement of construction-related noise levels that may be required to meet the contract specifications.

The contractor may also receive on-site training related to the noise-specific issues and noise-critical areas and sites adjacent to the project. Equipment manufacturers and/or suppliers may be available to provide training to the contractor concerning the proper use of the noise abatement features of specific pieces of their construction equipment. Any training requirements that are envisioned to be required would typically be described or referenced within the contract’s specifications and special provisions.

7.4 Mitigation at the Source

Source control is, in general, the most effective form of noise mitigation and involves controlling a noise source before it is able to emit potentially offensive noise levels. Construction noise (exclusive of blasting) is typically generated by two source types.

• Stationary equipment; and
• Mobile equipment.

7.4.1 Equipment – All Types.
The following discussions relate to both stationary and mobile construction equipment:.

• Use less noisy equipment: One of the most effective methods of diminishing the noise impacts caused by individual equipment is to use less noisy machinery. By specifying and/or using less noisy equipment, the impacts produced can be greatly reduced or in some cases, eliminated. Source control requirements may have the added benefits of promoting technological advances in the development of quieter equipment.

Figure 7.12. In some instances, using a less noisy piece of equipment (right) may be possible, as opposed to using more conventional and sometimes noisier equipment (left) to perform the same operation. (Photos #505 and #506)

• Mufflers: Most construction noise originates from internal combustion engines. A large part of the noise emitted is due to air intake and exhaust cycle. Specifying the use of adequate muffler systems can control much of this engine noise.

Figure 7.13. Muffler system on recycling equipment. (Photo #1287)

• Shields: Employing shields that are physically attached to the particular piece of equipment is quite effective, particularly for stationary equipment and where considerable noise reduction is required.

Figure 7.14. Unshielded, non-baffled equipment. (Photo #74)	Figure 7.15. Shielded compressor. (Photo #18)

• Dampeners: Equipment modifications such as dampening of metal surfaces, is quite effective in reducing noise due to vibration. Another possibility is the redesign of a particular piece of equipment to achieve uieter noise levels.

Figure 7.16. Examples of pile driver shielding and dampening. (Photos #1277, #1281, and #1308)

• Bubble Curtains: Where piles are driven or drilled through water, bubble curtain technology may be employed. Bubble curtain techniques introduce specifically sized air bubbles into the water surrounding the pile in a controlled manner, thus dampening the shock waves and helping to minimize the effects on aquatic life. Air may be released in a variety of ways, including through a ring as shown in the photo below. See References 030, 036, 046, 054, 060, 061, and 102 for information related to aquatic effects.

Figure 7.17. Bubble curtain. (Photo #57)

Figure 7.18. Bubble curtain air release ring. (Photo #51)	Figure 7.19. Bubble curtain. (Photo #52)

• Aprons: Sound aprons generally take the form of sound absorptive mats hung from the equipment or on frames attached to the equipment. The aprons can be constructed of rubber, lead-filled fabric, or PVC layers with possibly sound absorptive material covering the side facing the machine. Sound aprons are useful when the shielding must be frequently removed or if only partial covering is possible.

• Enclosures: Enclosures for stationary work may be constructed of wood or any other suitable material and typically surround the specific operation area and equipment. The walls could be lined with sound absorptive material to prevent an increase of sound levels within the structure. They should be designed for ease of erection and dismantling.

Figure 7.20. Straw bail enclosure for stationary equipment. (Photo #58)

• Blasting Mats: These mats are typically made with layers of used tires cabled together. They are commonly used as blankets for blasting operations to control and confine debris. These mats also provide a degree of noise attenuation from the blast. However, they do not mitigate vibration, which is usually more of a concern than noise.

Figure 7.21. Blasting mats constructed with black tires (in foreground of photo. (Photo #261)	Figure 7.22. Blasting mats being placed into position. (Photo #1341)

• Selection of Equipment: Newer equipment is generally quieter than old equipment for many reasons including technological advancements and the lack of worn, loose, or damaged components. Some equipment manufacturers have made their equipment quieter in recent years and have achieved significant reductions over older equipment. In some cases, the use of over or under-powered equipment may be an unexpected source of excessive noise. The type of engines and power transfer methods also plays a significant roll in achieving lowered equipment noise. The use of electric powered equipment is typically quieter than diesel, and hydraulic powered equipment is quieter than pneumatic power.

Figure 7.23. Older equipment may be as efficient as new, but may not meet noise emission requirements. (Photo #809)

Figure 7.24. Newer paving equipment. (Photo #813)

• Maintenance Programs: Poor maintenance of equipment typically causes excessive noise levels. Faulty or damaged mufflers, loose engine parts such as screws, bolts, or metal plates contribute to increased noise levels. Removal of noise-reducing attachments and devices such as mufflers, silencers, covers, guards, vibration isolators, etc. will, to varying degrees, increase noise emission levels. Old equipment may be made quieter by simple modifications, such as adding new mufflers or sound absorbing materials. Loose and worn parts should be fixed as soon as possible.

• Equipment Operation Training: Careless or improper operation or inappropriate use of equipment can increase noise levels. Poor loading, unloading, excavation, and hauling techniques are examples of how lack of adequate guidance and training may lead to increased noise levels.

Figure 7.25. Regular service of equipment is an essential component to quietest operation possible. Equipment suppliers may also be valuable sources of training related to proper use of equipment. (Photo #827)

7.4.2 Stationary Equipment.
Whenever possible, positioning stationary noise sources such as generators and compressors as far away as possible from noise sensitive areas should be considered. Temporary barriers can be employed and/or enclosures can be built around noisy equipment. These techniques can significantly reduce noise levels and, in many cases, are relatively inexpensive. These barriers can typically be constructed on the work site from common construction building material (plywood, block, stacks, or spoils). Enclosures are often constructed from commercial panels lined with sound absorbing material to achieve the maximum possible shielding effect.

Figure 7.26. Temporary shielding of stationary equipment. (Photo #1340)

To be effective, the length of a barrier should be greater than its height, the noise source should not be visible, and any barrier should be located as close as possible to either the noise source or the receiver. In addition, providing increased distance between a noise source and a noise receiver can also be considered a form of abatement.

Figure 7.27. Temporary barrier around stationary activity. (Photo #1339)

7.4.3 Mobile Equipment.
Many construction operations are mobile and tend to progress along the length of a project at varying rates. Noise levels at the receiver tend to vary considerably, not only as the speed and power of the equipment varies, but also as the equipment is constantly changing in terms of its distance to the receivers and its relative location. To address this, all the equipment noise mitigation techniques listed in Section 7.4.1 are worthy of consideration with the exception of the enclosures. Enclosing mobile equipment is usually not possible, unless the operation is slow moving and the enclosures can be easily moved.

7.5 Mitigation along the Path
In some situations, such as in urban areas or on isolated sections of a project, it may be beneficial and necessary to construct barriers adjacent to the work area or at the right-of-way. These can take the form of natural shielding, temporary shielding, and/or permanent shielding.

7.5.1 Existing Features.
Utilizing existing shielding such as berms, existing noise barriers, or structures for relatively static equipment such as pumps, generators, compressors, air ventilation, batch plants, and storage areas may be appropriate.

Figure 7.28. Existing noise barrier left in place until replacement noise barrier is constructed. (Photo #483)

Figure 7.29. Equipment and storage area shielded by existing structures. (Photo #558)

7.5.2 Temporary Abatement.

Advantage may also be taken of the screening effect of any nearby object such as parapet walls, buildings, trailers, or temporary site offices.

Figure 7.30. Use of existing structure and temporary plywood on chain link fence plus absorptive mats to shield recycling equipment. (Photos #690, #390, #395, and #679)

Figure 7.31. Temporary barrier of plastic material. (Photo #194)

Other temporary abatement techniques include the use of temporary and/or movable shielding for both specific and nonspecific operations. Some mobile shielding is capable of being moved intact or being repeatedly erected and dismantled to shield a moving operation. An example of such a barrier utilizes noise curtains in conjunction with trailers to create an easily movable, temporary noise barrier system.

Figure 7.32. Storage trailers modified to act as temporary noise barrier. (Photos #1030 and #1029)

7.5.3 Early Construction of Permanent Noise Barriers.
As mentioned in Section 7.2.2, shielding of certain construction activities may be accomplished by specifying that the construction of permanent noise barriers be implemented as early as possible during the project’s construction phase. Obviously, some noise-producing activities will likely be required before such barriers can be constructed. In addition, the actual erection of the noise barriers is a noise generating activity.

Figure 7.33. Early construction of permanent noise barriers. (Photo #472)

7.6 Mitigation at the Receiver

Mitigation at a receiver can be vary in its complexity, ranging anywhere from relocating residents for a day to insulation of a building. Even after mitigation measures have been applied, the outcome may still be unpredictable with no guarantees that the implemented methods achieve expected results. Therefore, mitigation at the receiver should only be considered as a last alternative. However, there are cases where creative techniques have been successfully implemented.

7.6.1 Building Envelope Improvements.
Building envelope mitigation techniques to reduce construction noise can include items such as sealing existing building elements, providing new sealed windows and doors, adding building insulation, etc. Such techniques, while effective, may also require modification of the building’s heating, ventilation, and air conditioning system. Prior to proposing such treatments, thorough consideration of the costs and implications of such modifications is strongly suggested.

Figure 7.34. Installation of a complete air handling system and window treatments at urban school solely to abate construction noise due to future conversion of arterial to depressed expressway. (Photos #1300, #1303, and #1304)

The following discussion of window treatments is based on information provided in Reference 009. The reader is directed to this reference document for more information.

Acoustical window treatments to improve the noise reduction qualities of residential window openings represents a proven successful means to implement receptor noise control. In general, window openings are the weak link in a structure’s external facade allowing noise infiltration into the building. When properly specified and installed, window treatments can provide for a significantly quieter interior noise environment, particularly in multi-story buildings with upper floors that may not benefit from typical noise barriers. In general, window treatments are most cost-effective when a relatively few or widely scattered number of receptors require noise mitigation. Window treatments have the added attraction of reducing noise from all noise sources, such as traffic noise, aircraft noise, and general community noise, in addition to reducing construction noise.

Several forms of acoustical window treatments are available. Each has its pros and cons:

• Interior glass sash – simple to install, least costly, good noise reduction, no historic restrictions, but limits sill space;
• Temporary interior clear vinyl curtains – simple and quick, inexpensive, but somewhat unattractive;
• Full replacement acoustical windows – double or triple pane glass, excellent noise reduction, but expensive; and
• Exterior storm sash – inexpensive, marginal additional noise reduction, subject to historic preservation limitations.

• Legal concerns;
• Labor agreements;
• Historic preservation issues;
• Procurement schedules;
• Staffing requirements;
• Cost implications;
• Contractor scheduling; and
• Correspondence with eligible recipients.

7.6.2 Noise Masking.
Noise masking is a technique that is still in the developmental stage, but may have potential in isolated cases. Masking considerations could include techniques such as constructing water falls or other cascading water designs, employment of noise cancellation technologies, changing “background” noise levels, etc. Such techniques require the consideration of the type of noise generator (stationary, mobile, etc.), the source’s noise frequency content, variability of the noise source in terms of its magnitude and duration, and the noise environment of the receptor being protected.

Figure 7.35. Experimental sound system used to mask nighttime construction noise in the community. (Photos #42 and #38)

7.6.3 Relocation of Residents.
In certain instances it may be appropriate, and possibly more cost-effective, to temporarily relocate a resident or residents from the construction area. By temporarily eliminating the noise receptor, noisy construction activities may be able to be undertaken unimpeded and completed in far less time than would be required under a noise-restrictive procedure. Such a technique was employed when several spans of a damaged interstate highway structure required demolition in close proximity to a row of residences. The residents were relocated to a hotel for a weekend while the damaged bridge structure was completely demolished. Another project which included relocation of residents as a mitigation measure is discussed in Reference 103.

7.7 Selection of Mitigation Measures

After the potential impacts resulting from the construction activities have been established, the next step in the process is the selection of appropriate control measures to be implemented on the project. This can typically be accomplished by identifying all feasible measures that could be used, selecting the most suitable techniques, and assembling them into a final mitigation strategy.

7.7.1 Identification of Feasible and Reasonable Measures.

This stage involves identification of control strategies which could be implemented to bring about the desired reductions in noise impacts. Some of the factors that influence this identification process are:

• Amount of reduction needed;
• Local sentiment toward the proposed project;
• Local noise ordinances;
• Length of the construction period;
• Effectiveness of control strategies; and
• Cost of control strategies.

• Cost;
• Practicality;
• Achievable noise reduction; and
• Effect on overall project operation.

7.7.2 Selection of Mitigation Strategies.
This stage involves the selection of a reasonable control strategy from the methods examined in the identification stage. The measure or measures chosen should be weighed as to their benefits compared to their adverse effects. This weighting should take into consideration:

• Monetary costs involved;
• Feasibility of carrying out the mitigation techniques;
• Problems with implementation of the method;
• Ability to enforce any requirements of the strategy;
• Degree of noise reduction achievable;
• Gauging the sensitivity of the receptors in the area; and
• Evaluation of the strategy with regard to any adverse impact on the overall operation of the project caused by delays or disruption of critical construction scheduling.

7.8 Monitoring Noise Levels During Construction

Regardless of the types of noise abatement strategies and techniques employed on any particular project, successes or failures are ultimately determined by resultant effects on noise levels at sensitive sites and the adherence of the resultant noise levels to the stated construction noise level criteria.

Evaluation of such success or failure is typically addressed by a program, the requirements of which are usually detailed in the contract specifications and special provisions. An adequate program requires:

• Properly trained staff for the task of monitoring noise;
• Equipment sufficient to properly monitor noise levels and operations;
• Well-written specifications to avoid misinterpretations;
• Well-defined goals that can be achieved and measured;
• Knowledgeable and properly trained operators and contractors who have an understanding of what has to be achieved, why it has to be achieved, and how to achieve it; and
• Clearly defined chain of responsibility to ensure compliance in a timely and proper manner.

• Empowerment of staff;
• Clearly defined consequences; and
• Dispute resolution mechanism.

7.9 Examples of Construction Noise Regulations

While 23 CFR 772 requires the evaluation of construction noise and the consideration of mitigation for identified construction noise impacts, it does not include specifications or specific language related to construction noise mitigation techniques, criteria, or restrictions. Such detail is included in various State and local documents, some of which are included as References 001, 009, 053, 077, and 103 and/or referred to in Table 10.1 of this Handbook.

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