A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity (2012)

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29 The FHWA commitment to minimizing noise impacts and enhancing the noise environment is described in Title 23 CFR Part 772—Procedures for Abatement of Highway Traffic Noise and Construction Noise. This regulation addresses noise impact assessment and abatement. In addition, each STA is empowered to define certain terms and conditions found in 23 CFR 772, such as the cost-effectiveness criteria by which candidate noise mitigation measures are evaluated for feasibility and reasonableness. Typically these cost-effectiveness guidelines account for the cost of a given mitigation measure (e.g., noise barrier), the decibel reduction, and the number of people or properties (dwelling units, businesses) expected to benefit from the mitigation. Key Take-Away 23 CFR 772.11 (g) The plans and specifications will not be approved by the FHWA unless those noise abatement measures that are reasonable and feasible are incorporated into the plans and specifications to reduce or eliminate the noise impact on existing activities, developed lands, or undeveloped lands for which development is planned, designed, and programmed. However, FHWA and state DOT guidelines do not mandate that construction noise be evaluated and/or mitigated in any specific manner; they simply provide guidelines and recommendations for each project to adopt on a case-by-case basis. Project design and contract documents can address nuisances by specifying the sequencing of construction operations to minimize nuisance impacts. Practices such as source, path, and receptor control are helpful in eliminating or minimizing the effect of nighttime construction nuisances. The major nuisances associated with nighttime construction are noise, illumination, and vibration (Schexnayder and Ernzen 1999). Noise problems are normally caused by the opera- tion of heavy equipment and specifically by vehicle and machine backup alarms. While good illumination is necessary for the work to proceed at night and for the safety of the traveling public, proper work-zone illumination can be very intrusive to project neighbors. Vibration problems are primarily a result of pile driving, hoe ram demolition, blasting operations, or the use of vibratory rollers. Agencies need to be aware that they are exposed to possible contractor claims if noise limitations are not properly stated in contract documents. Contract documents must be checked to ensure there are no conflicts between bonus clauses for early completion and specifications limiting work activities to daytime hours because of community noise regulations. C H A P T E R 4 Nuisances

30 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity The problems associated with nighttime construction are location dependent. Nighttime con- struction can cause nuisances when the work is in residential and commercial areas, whereas few problems arise in rural settings or when resurfacing a highway in an industrial area. From earlier studies, it is evident that for projects involving nighttime work, the “contract documents must clearly define work restrictions (e.g., work hour restrictions, vibration and noise restrictions, and any regulations that will limit work or logistic activities). These restric- tions must be further delineated as to their application to activities during daylight hours or to evening and nighttime hours with definitions of the terms daylight, evening, and nighttime clearly stated” (Anderson and Schexnayder 2009). Nuisance problems are a function of the nature of the nighttime work performed and the location of that work. Conversely, agencies experience limited nuisance problems when conduct- ing the nighttime activities of paving, patching, or resurfacing operations on Interstate highways. These operations typically take place where the background noise from the traffic masks the construction noise. In addition, this type of work involves operations that are constantly moving and, therefore, affect a receiver for only limited durations. STAs can control noise at the source by requiring adherence to certain noise (decibel) limits during nighttime construction or by prohibiting otherwise unmitigatable loud devices (such as pile drivers). In many cases, limits are the consequence of specific local ordinances. While in some locations STAs do not have to abide by city regulations, the contract language should still make contractors aware of the noise ordinance and hold them in conformance. Figure 4.1 has the contract language used to inform contractors of the Jacksonville, Florida, noise ordinance. FHWA Noise Guidance Documents The FHWA Environmental Policy Statement establishes a commitment to ensure that all feasible and reasonable mitigation measures are incorporated into projects to minimize noise impacts and enhance the surrounding noise environment to the extent practicable. This commitment to mini- mize noise impacts and enhance the noise environment is described in the FHWA noise regulation, Title 23 CFR Part 772—Procedures for Abatement of Highway Traffic Noise and Construction Noise. Resource FHWA is the primary regulatory authority regarding noise impact assessment and abatement. Title 23 CFR Part 772—Procedures for Abatement of Highway Traffic Noise and Construction Noise is available online at www.fhwa.dot.gov/legsregs/directives/fapg/cfr0772.htm. Note that FHWA updated 23 CFR Part 772, effective July 13, 2011, to place more responsibility on STAs to define acceptable mitigation criteria. However, the portion of 23 CFR Part 772 that deals with construction noise (Section 772.19) remained essentially unchanged, as shown in Figure 4.2. FDOT Standard Specifications: Section 7, Article 7-1 Laws to be Observed, Sub-article 7-1.1, “The contractor is required to become familiar with and comply with all Federal, State, county and city laws, by-laws, ordinances and regulations that control the actions or operation of those engaged or employed in the work or that affect materials used.” FDOT Standard Specifications: Section 8, Article 8-4 Limitations of Operations, Sub-article 8-4.1, “Night Work,” “The contractor is required to comply with all applicable regulations governing noise abatement.” Plan Sheet M-13 Pile Driving, Note 1 stated, “All pile driving activities are subject to the Noise Ordinance of the City of Jacksonville.” Figure 4.1. Sample noise ordinance contract language.

Nuisances 31 To support agencies in their efforts to control construction noise nuisances, FHWA sponsored development of a Construction Noise Handbook (FHWA 2006a) and associated FHWA Roadway Construction Noise Model (FHWA RCNM) (FHWA 2006b). This handbook and noise prediction model spreadsheet are the successors to the 1977 Special Report—Highway Construction Noise: Measurement, Prediction and Mitigation (Reagan and Grant 1977). Supporting the 1977 Special Report was a Symposium on Highway Construction Noise report by Dames & Moore (1977) that also provides information to address construction noise problems. Resources • Construction Noise Handbook http://www.fhwa.dot.gov/environment/noise/construction_noise/handbook/index.cf • FHWA Roadway Construction Noise Model (FHWA RCNM) http://www.fhwa.dot.gov/environment/noise/construction_noise/rcnm/rcnm.cfm There are a number of construction-noise case histories that focus attention on construction noise evaluation and control. A recent example is that of the Central Artery/Tunnel (CA/T) project (also known unofficially as the Big Dig) in Boston, Massachusetts, which proved that mega-project construction noise can be controlled satisfactorily while the work proceeds (Thalheimer 2000). Sound Sound is energy in motion as a pressure wave through the air produced by a vibrating body. A decibel (dB) is the basic sound level unit; it denotes a ratio of intensity to a reference sound. Most sounds that humans are capable of hearing have a decibel range of 0 to 140. Zero dB, by international agreement, corresponds to an air pressure level of 20 micro-Pascals (in other words, the agreed-upon threshold of hearing). A whisper is about 30 dB, conversational speech is about 60 dB, and 130 dB is the threshold of physical pain. Humans sense the intensity difference of one sound from another. A three-decibel change in noise level is a barely noticeable difference, while a 10-dB change is perceived subjectively as a doubling/halving in loudness. In the case of the general population, a five-decibel change is easily noticeable by most people. To facilitate the measurement of sound stimuli perceived by humans, a weighted decibel scale (called A-weighted) is used to simulate the frequencies heard by humans. A decibel that is measured or calculated using this frequency adjustment is called an A-weighted decibel, and abbreviated as dBA. Sound fluctuates with time and is emitted from multiple sources from moment to moment; consequently, the common practice is to evaluate the temporal characteristics of sound with various statistical metrics much as its maximum (Lmax) or minimum (Lmin) levels. One of the more common metrics is the equivalent sound level, or Leq, which amalgamates all sound Figure 4.2. FHWA construction noise mitigation requirements. Section 772.19, which is very short, deals with construction noise and identifies three general steps to perform for all projects: • 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. • 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 as well as the costs of the abatement measures. • Incorporate the needed abatement measures in the plans and specifications.

32 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity information into a single energy-averaged level. The Leq value is the average acoustic intensity over a defined time period and represents the equivalent energy level of a fluctuating sound, had that sound been steady over the time period. Environmental sound can also be presented on a statistical basis using percentile sound levels (Ln), which refer to the sound level exceeded for a specified percent of the time. Thus, an L10 nomenclature would mean an A-weighted sound level exceeded 10 percent of the time. In the case of construction noise, the L10 has often been found to be about three decibels greater than the Leq level and correlates well with construction activity (Thalheimer 2000). When dealing with the public, sound and noise are not the same thing. While sound is prefer- able and pleasant, it can become noise when any of the following occurs with regard to the sound for the receiver: • Too loud. • Unexpected. • Uncontrollable. • Pure tone components. Noise is any sound that has the potential to annoy or disturb humans, or cause an adverse psychological or physiological effect on humans. Equipment Noise Most construction noise is the result of equipment operation. The equipment type, specific model, equipment condition, and operation being performed influence equipment noise. Newer equipment is noticeably quieter than older models, due primarily to better engine housings and mufflers, and fan design. Table 4.1 shows noise levels generated by typical equipment. Noise Control Physical noise control seeks a reduction and/or modification of a perceived sound field. It strives to change the noise level or impact at the receiver. Mitigation of annoying noise should consider source, path, and receptor control. However, noise is also psychological. Therefore, community involvement is a critical component of noise nuisance mitigation. Nuisance issues can be defused substantially by recognition of community concerns and a willingness to address specific concerns. Resource The FHWA construction noise website at www.fhwa.dot.gov/environment/noise/construction_ noise contains these important resources: • Construction Noise Handbook prepared by the John A. Volpe National Transportation Systems Center. • FHWA Roadway Construction Noise Model prediction spreadsheet. • Highway Construction Noise—Measurement, Prediction, and Mitigation Manual. Community Involvement Community involvement is a vital part of every nuisance mitigation program, whether the issue is noise, vibration, or light. Maintaining positive community relations in unison with phy- sical nuisance monitoring and mitigation measures is important. Public involvement helps to eliminate potential problems before they become major issues.

Nuisances 33 Tip Effective community awareness techniques: • Personal contact via door-to-door visits or special gatherings. • Personalized letters. • Newspaper and radio announcements. • Website-based project information. By working with local government officials, businesses, and individuals located adjacent to the project, it is possible to identify and address nuisances. A good practice is to conduct public meetings even if they are not mandatory. Table 4.1. Construction equipment noise emission levels (Thalheimer 2000, originally from CA/T Project, adopted by FHWA RCNM and NYCDEP Rules). Equipment Type or Activity Lmax Noise Limit at 50 ft, Slow (dB) Is Equipment an Impact Device? Acoustic Usage Factor (%) Auger drill rig 85 No 20 Backhoe 80 No 40 Blasting 94 Yes 1 Chain saw 85 No 20 Compactor (ground) 80 No 20 Compressor (air) 80 No 40 Concrete batch plant 83 No 15 Concrete mixer truck 85 No 40 Concrete pump 82 No 20 Concrete saw 90 No 20 Crane 85 No 20 Dozer 85 No 40 Dump truck 84 No 40 Excavator 85 No 40 Flatbed truck 84 No 40 Front-end loader 80 No 40 Generator (≤25 KVA) 70 No 50 Generator (>25 KVA) 82 No 50 Grader 85 No 40 Boring hydraulic jack 80 No 25 Impact pile driver 95 Yes 20 Jackhammer 85 Yes 20 Hoe ram 90 Yes 20 Paver 85 No 50 Pickup truck 55 No 40 Pneumatic tools 85 No 50 Pumps 77 No 50 Rock drill 85 No 20 Scraper 85 No 40 Slurry plant 78 No 100 Slurry trenching machine 82 No 50 Soil mix drill rig 80 No 50 Tractor 84 No 40 Vacuum street sweeper 80 No 10 Vibratory concrete mixer 80 No 20 Vibratory pile driver 95 No 20 Welder 73 No 40 NYCDEP = New York City Department of Environmental Protection. KVA = Kilovolt amperes. Impact Device = Equipment is assumed to produce separate discernible sound pressure maxima. Acoustic Usage Factor = Percentage of time equipment is assumed to be running at full power while working on site.

34 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity Public meetings are important for receiving feedback and in providing early identification of controversial issues. It is imperative to explain the details of construction phasing and methods and the resulting noise, vibrations, and other nuisances. Likewise, steps to minimize impacts should be stated clearly and project contact information given in case a member of the public feels the need to register a complaint. All outcomes from communications with the public need to become part of the applicable environmental record. Approved noise abatement measures should also be documented in the appropriate environmental commitments. Tip Communications need to educate the public about the following: • Positive impacts of the completed project (highlight improvements). • What to expect—work hours, type of work, type of equipment, and nuisance duration. • Actions to mitigate nuisances. • Where to get more information. • How to voice complaints. It is important to provide accurate and easily accessible information. Depending on the size and scope of the project, different methods can be used to inform the public or to ensure that affected neighbors are informed. The other equally important part of successful communications is listening. The agency needs to show sensitivity to community concerns and respect for residents and business owners. A significant portion of the listening and response effort will be simply to answer questions. Listening and sensitivity create and strengthen a bond of trust with affected individuals. Tip Inform the public via the following: • Door-to-door visits. • Neighborhood letters or fact sheets. • Local media, newspaper notices, press releases, news conferences. • Public informational workshops. • Information kiosks in public areas (shopping malls). • Speakers bureau. • Brochures/newsletters. • Project websites. Complaints will arise during the construction phase, so an established procedure for receiv- ing, tracking, and ensuring a timely response to all grievances is needed. Procedures for handling complaints effectively include the following: • Have a knowledgeable individual to field all questions. • Establish a hotline to receive and log any/all queries. • Develop a system to ensure that all queries are answered in a timely manner. • Anticipate potential impacts and have a plan in place to minimize those impacts. Have trained project staff that are able to respond to complaints immediately, investigate/ evaluate the severity thereof, and order immediate mitigating actions if the situation warrants.

Nuisances 35 Tip Provide project inspectors with cell phones to ensure a quick response to citizen inquiries and complaints. In the case of a major project, inquiry calls can be processed through a central control center, which then notifies the correct inspector. However, for small jobs, the inspector’s number should be posted and circulated in the abutting neighborhood. While noise is usually the primary cause of nuisance complaints, visual impacts also draw attention to the construction process. Large trucks using residential streets for project access create noise, but they also draw attention to the work. All potential impacts are important considerations, so contract documents need to include appropriate restrictions. When a project is located close to businesses and sound barriers are speci- fied, it may be necessary to include requirements concerning their exterior appearance. Replacement signage may be necessary to maintain public awareness of and access to commercial storefronts. Source Control Source control is the most effective method of eliminating noise problems. Source controls, which limit or avoid noise emissions, are the easiest to oversee on the project. An agency has complete control of the project site and can specify source noise limitations. Once a sound is created, path control methods can be used, but those control techniques only provide partial control of the nuisance. Source control preempts alternative mitigation efforts. Table 4.2 provides rules of thumb for evaluating the ease and effectiveness of mitigating noise problems. For example, if two sources are each contributing 60 dBA at a receptor location, the additive or total noise will be 63 dBA as shown in Table 4.3. Conversely, if two noise sources differ by more than 10 decibels, the contribution of the quieter source can be ignored when considering the overall level (L). Key Take-Away The noise of each individual piece of equipment, even the loudest noise source, is not always the number one priority. Decibels are logarithmic quantities, not linear; therefore, sound levels cannot simply be added, subtracted, or averaged together. Source Control through Design Considerations and Specifications Early communications between project designers and the community can aid greatly in sequencing construction operations to minimize construction noise impacts at sensitive recep- tors. Abatement measures need to be incorporated into the plans and specifications of the project. Table 4.2. Source control mitigation by decibel reduction and difficulty level (Schexnayder and Ernzen 1999). Decibel Reduction Difficulty Level Typical Mitigation 5 Simple Require new equipment 10 Attainable Equipment modification 15 Very difficult Possibly by going to alternate methods 20 Nearly impossible Table 4.3. Addition of sound levels, L1 and L2 (L1 > L2) (Schexnayder and Ernzen 1999). L1 - L2 (dBA) Add to L1 (dBA) 0 or 1 3 2 or 3 2 4 to 8 2 ≥ 9 0

36 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity Project specifications should require that permanent noise barriers (as in traffic noise barriers) be constructed as early as possible to decrease potential construction noise impacts. Alternate construction methods and equipment can also be suggested or specified to lessen potential con- struction noise impacts (such as cast-in-place piles rather than driven piles). Specifications. Good controlling specifications are an effective tool in mitigating the effect of construction noise nuisances. Supplemental standard provisions can specify mitigation mea- sures on a contract-by-contract basis to address special local-condition noise. The existence and importance of noise control specifications need to be emphasized at pre-bid and pre-construction conferences. When the requirement to comply with all restrictions and commitments to local governing bodies is included in the contract documents, contractors can be expected to allow for compli- ance in the bid price. Such an approach allows contractors to plan their operations effectively and to seek innovative solutions to the clearly identified problem. This approach minimizes potential complaints and serves to control construction cost and delays. It is often too late to control a contractor’s noise by contractual means once work has begun. Therefore, a comprehensive noise control specification must be developed proactively and included in the project bid documents. Doing so will ensure the lowest cost through the com- petitive bid process and give project managers the means to oversee and direct the contractor in noise-related matters, should field conditions dictate the necessity. Contract specification tasks include the following: • Develop contract-specific nuisance evaluation measures. • Identify noise-sensitive receptors. • Develop criteria for lot-line and/or emission-noise limits. • Prohibit specific types of construction activities (certain types of activities can generate noise complaints even though their sound levels do not exceed emission limits, and this is especially true for rattling, banging, tonal, and repetitive sounds). • Set equipment noise emission limits (see Table 4.1 for typical noise emission levels). • Establish operational (working-hour) constraints. • Provide noise abatement incentives for contractors (it may be effective to pay bonuses for staying below noise standards over certain contract periods). • Include provisions for temporary variances. • Detail required submittals of mitigation measures. • Require contractors to prepare detailed noise mitigation plans. As a minimum, the contractor’s noise mitigation plan should include the following: • Name of responsible party with phone number. • Distance to receptors for each major noise-generating activity. • Dates and hours of work by principal type or phase of work. • Major noise-generating equipment or activity. • Estimate of construction noise levels at receptors. • List of noise mitigation measures and the expected noise reduction. Resource The New York City Department of Environmental Protection (NYCDEP) Construction Noise Mitigation Plan sample form can be found at http://nyc.gov/html/dep/pdf/noise_mitigation. pdf. The sample explains to the user the required plan elements that a responsible party must include when the listed devices will be used on a construction site (NYCDEP 2007).

Nuisances 37 When an agency writes requirements based on Table 4.4 and the associated Tip into a project specification, the contractor must comply with both relative lot-line noise limits and abso- lute equipment sound emissions. Such source control actions serve as measurable contract performance limits against which noise complaints can be evaluated. If conditions causing a noise complaint are found to exceed specified limits, project staff can order the contractor to implement additional mitigation, or even stop work, without fear of incurring a claim from the contractor for unjustified cost or delay. Tip Equipment Specification Absolute Noise Criteria The contract can set “absolute” sound criteria for generic classes of equipment. The data in Table 4.1 are the equipment-specific Lmax noise limits in A-weighted decibels, evaluated at a ref- erence distance of 50 ft, which were specified by the CA/T project in Boston. These limits were set conservatively low to require the use of modern, well-maintained equipment. Every piece of equipment must be pre-certified by the contractor’s acoustical engineer before the machine is allowed to work on the project site. Other Specification Items. Specifications must be definitive with actual times or other requirements stated clearly; otherwise, there will be contractor versus agency confrontation concerning implementation of the specifications. Other noise source control items that agencies have written into specifications include the following: • The use of impact pile drivers and hoe rams shall be prohibited during evening and nighttime hours. • All jackhammers and pavement breakers used on the construction site shall be fitted with manufacturer’s approved exhaust mufflers. • The use of pneumatic impact equipment (i.e., pavement breakers, jackhammers) shall be prohibited within 200 ft of a noise-sensitive location during nighttime hours. • The local power grid shall be used wherever feasible to limit generator noise. No generators larger than 25 kilovolt amperes (KVA) shall be used and, where a generator is necessary, it shall have a maximum noise muffling capacity. • The contractor shall minimize noise from the use of backup alarms using measures that meet OSHA (Occupational Safety and Health Administration) regulations. This allows for use of self-adjusting backup alarms, use of manual alarms on low setting, use of observers, and scheduling of activities so that alarm noise is minimized (straight drive-through haul patterns) or Table 4.4. Construction noise limits by receiver lot-line land use and time of day (CA/T Project, Boston). Land Use Daytime (7 a.m. – 6 p.m.) L10 Lmax Evening (6 p.m. – 10 p.m.) L10 L10 Night (10 p.m. – 7 a.m.) Noise- sensitive (Residential) 75 or Baseline +5 85 90 Impact Baseline +5 85 Baseline+5 if <70 Baseline+3 if ≥ 70 80 Commercial 80 or Baseline +5 none none none none none Industrial 85 or Baseline +5 none none none none none Lmax Lmax

38 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity • All equipment with backup alarms operated by the contractor, vendors, suppliers, and sub- contractors on the construction site shall be equipped with either audible self-adjusting backup alarms or manual adjustable alarms. The self-adjusting backup alarms shall auto- matically adjust to five decibels over the surrounding background noise levels. The manually adjustable alarms shall be set at the lowest setting required to be audible above the sur- rounding noise. Installation and use of the alarms shall be consistent with the performance requirements of the current revisions of the Society of Automotive Engineering (SAE) J994, J446, and OSHA requirements. • All variable message/sign boards shall be solar powered or connected to the local power grid. • Material storage areas will be restricted from areas near residences. • Contractors shall use approved haul routes to minimize noise at residential and other sensitive noise receptor sites. • A construction noise monitoring program is essential to reassure the public, evaluate any noise complaints, and hold the contractor accountable to noise limits. Sometimes an agency will even specify the sequence of operations/activities (order of pile driving, work zones close to abutters only during the daytime, other zones at any time). Noise Monitoring Program Depending on the type and comprehensiveness of the noise control specification, noise measurements may need to be performed at neighborhood receptor locations prior to con- struction to determine ambient noise conditions. These ambient measurements are usu- ally performed over several days and nights, including weekday and weekend time periods. The results can then be used to establish acceptable noise criteria limits when construction begins. Noise measurements need to be performed during construction to ensure that the contrac- tor operations are within established noise limits. Noise monitoring during construction can include measuring cumulative noise at various locations to evaluate compliance with receptor noise limits or noise levels in close proximity to equipment working on a site to ensure acceptable equipment noise emission levels (see Table 4.1). Tip The instrumentation used to measure ambient and/or construction noise levels should com- ply with ANSI Standard S1.4 for Type 1 or Type 2 accuracy. Common noise metrics that are found in various project noise control specifications include the Lmax, the Leq, and statistical levels (L10, L90) exceeded a given percentage of the time. Unless otherwise specified, noise lev- els should be measured in A-weighted decibels using a root-mean-square (RMS) “slow” time response. Path Control Having exhausted all possible mitigation methods of controlling noise at the source, the sec- ond line of attack is to control noise propagation along its pathway. Noise barriers can provide a substantial reduction in noise levels and are cost effective, but their use must be implemented in a practical manner without limiting work-area access. Barriers do increase a project’s visual impact. This visual change can have either a positive or a negative impact, because equipment that is out of sight is often perceived as being less annoy- ing. Therefore, aesthetic effects must be considered when designing barrier systems (Farnham and Beimborn 1991).

Nuisances 39 Key Take-Away Physical Placement and Height of the Barrier Wall Control Effectiveness When placed properly, a noise barrier can provide 5 to 20 decibels of noise reduction from a listener’s perspective. The barrier must intervene and completely break the line of sight between the noise source and the receptor. Therefore, the barrier should be placed as close to the noise source or as close to the receptor as possible. The limiting aspect for a barrier’s noise reduction performance is the noise diffracting over the top of the barrier. To ensure that noise does not transit directly through the barrier, its surface density should be 3 lbs per sq ft or greater. Many common barrier materials satisfy this surface density requirement including wooden timbers, lightweight concrete, dense plastics, or engineered metal panels. Because of practical height limitations for building temporary barriers, mitigating noise that affects the upper stories of tall buildings with barriers can be difficult. Therefore, while the pri- mary intent is for mitigation of ground floors and outdoor use areas, further analysis may be performed in an attempt to mitigate noise for higher floors as site-specific terrain conditions allow. However, extreme care must be practiced when erecting taller noise barriers to ensure they do not tip over due to wind load and, in certain locations, a seismic evaluation is also advisable. Path Mitigation Techniques Only reflection, diffraction, insulation, or dissipation can modify an established airborne sound field. Therefore, the three techniques for path mitigation are as follows: • Distance. • Reflection. • Absorption. By doubling the distance between the source and the receiver, a 3 to 6 dB reduction can be achieved, and a 6 dB reduction represents a noticeable change in noise level. Barriers are intended primarily to reflect sound away from sensitive receptors effectively. However, the reflected sound energy can travel back toward the source and possibly have an impact on receptors in the other direction. In these cases, barriers with acoustically absorptive faces may be necessary. Absorption, while occasionally useful to avoid unwanted reflections or for use inside enclosures, should not be viewed as a practical construction noise pathway control measure by itself. Absorption does nothing to reduce the direct sound field and only works to absorb a portion of the sound that actually interacts with the absorptive materials. Enclose Stationary Equipment Enclosures can provide a 10 to 20 dB sound reduction; however, caution must be practiced to ensure that enclosed equipment has a sufficient air supply to operate and does not overheat. To be most effective, noise enclosures should cover a noise source completely without any gaps or holes that allow noise to escape. Whenever possible, it is advisable to line the inside of the enclosure with some type of acoustical absorptive material, taking care to avoid interfering with the operation of the equipment. Figure 4.3 shows an example of an enclosure specification. Noise Barriers and Curtains A 5 to 20 dB sound reduction can be achieved using barriers. A sound wave striking a barrier is affected in three ways: some of the sound energy is transmitted through the barrier, some is

40 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity absorbed within the material of the barrier, and the majority of the sound energy is reflected back toward the source. The ability of a barrier to resist the flow of sound energy is largely determined by its mass. Heavy, dense materials are good barriers, whereas soft, porous materials are poor barriers. A characteristic of a barrier that must always be considered is stiffness. A barrier constructed from a rigid material can transmit vibration and reradiate noise on the backside of the barrier. An approach to the reflected noise problem is to provide noise-absorptive surfaces on the side of the barrier wall facing the noise source. Barrier design and construction must incorporate consideration of aesthetics and public safety. A tall barrier placed close to a building façade can create a tunnel effect. The creation of such dark spaces can be dangerous to the public that must use the adjoining sidewalk. Barriers constructed of transparent materials (such as Plexiglas or Lexan) can be appropriate in such locations. A structural and wind load analysis must be conducted before erecting barriers. Thickly- grown non-deciduous bushes and trees can be effective in decreasing sound reflection from walls, but they do not provide noise shielding. Trees and shrubs should not be presented to the public as an effective noise barrier option. In general, noise barriers or curtains are most cost effective when they provide perceptible noise reduction benefits to a relatively large number of receptors. To provide this, the barrier must physically fit in the space available and completely break the line of sight between the noise source and the receptors. Tip A minimum performance requirement to justify barriers is a five-decibel noise reduction at receptor locations; however, it is not uncommon to see performance design goals in the 7 to 10 decibel range. Barrier Specifications. Solid barriers should be constructed of a material having a surface density of at least 3 lbs per sq ft to ensure adequate sound transmission loss. The most commonly used reference to quantify a material’s ability to decrease transmitted noise is its sound transmis- sion class (STC) rating. A material’s STC is determined in accordance with American Society for Testing and Materials (ASTM) Test Method E90 by measuring the noise energy reduction through the material as a function of frequency and then evaluating the results against a standard frequency-shaped curve with the resulting rating taken at 500 Hz. Key Take-Away Noise barriers should have STC ratings of at least 25, with 30 being a more desirable value. Gaps through or under noise barriers seriously degrade the sound-mitigating effect of a bar- rier. Gaps should be sealed with material that completely closes the openings and attenuates sound. However, access gaps are often required in barriers. At such locations, two barrier seg- ments should be overlapped to provide access. The overlap causes the sound to “bend” several times before heading toward the neighbors. A 15 to 20 foot overlap is generally sufficient. Figure 4.3. Sample enclosure specification. All jackhammers and pavement breakers used at the site shall be enclosed with shields or acoustical barrier enclosures.

Nuisances 41 Figure 4.4 shows an example of a noise barrier specification. Acoustical Curtains. Acoustical curtains are commercially-available mass-loaded heavy vinyl quilts that can reduce sound levels by about 5 to 10 decibels. Curtains are typically installed in vertical segments. All seams and joints should have a minimum overlap of 2 in. and be tightly sealed (e.g., with Velcro strips or wire ties). Figure 4.5 shows an example of an acoustical curtain specification. Receptor Control When all other approaches to noise control have been insufficient, control efforts at the receiver should be undertaken. It should be remembered that the critical receiver might not be human. Certain precision equipment or interior building space can require very low levels of ambient noise and vibration. Receptor Mitigation Techniques Receptor problems usually involve individuals located very close to the noise-generating activ- ity, in which case it may be more effective to improve the individual’s acoustic environment rather than controlling all emitted noise. Window Treatments. In general, window openings are the weak link in a structure’s external façade, allowing noise infiltration into the building. A good acoustical window treatment, such as interior or exterior storm sashes, can provide an incremental noise reduction improvement (beyond that provided by the original window) of 10 decibels within a building. Therefore, an acoustically-treated window, or a new triple-glazed acoustical window, for example, can provide a total outside-to-inside noise reduction of 35 decibels or more. Tip Window treatments are most cost effective when a relatively few or a widely-scattered number of receptors require noise mitigation. Figure 4.4. Sample barrier specification. Noise barriers shall break the line of sight between the noise source and the receptor, be made of material with a surface density of at least 3 lbs per sq ft, have a minimum STC rating of STC-30 according to ASTM Test Method E90, and be free of gaps or holes. When barrier units are joined together, the mating surfaces of the barrier sides shall be flush with each other. Gaps between barrier units, and between the bottom edge of the barrier panels and the ground, shall be closed with material that completely closes the gaps and is dense enough to attenuate noise. Figure 4.5. Sample acoustical curtain specification (FTMS  Federal Test Method Standard). The acoustical material shall be weather- and abuse-resistant and exhibit superior hanging and tear strength during construction. The material shall have a minimum breaking strength of 120 lbs per in. per FTMS 191 A-M5102 and minimum tear strength of 30 lbs per in. per ASTM D117. Based on the same test procedures, the absorptive material facing shall have a minimum breaking strength of 100 lbs per in. and minimum tear strength of 7 lbs per in. The acoustical material shall have an STC of STC-25 or greater, based on certified sound transmission loss data taken according to ASTM Test Method E90. It shall also have a Noise Reduction Coefficient rating of NRC 0.70 or greater, based on certified sound absorption coefficient data taken according to ASTM Test Method C423.

42 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity Figure 4.6 shows a sample window treatment program eligibility policy. If a treatment was approved, the CA/T project in Boston issued a task order to a window con- tractor. After the work was performed, a post-noise assessment was conducted. The contractor was paid by CA/T after the resident signed off on the completed work. Temporary Relocation. In very special cases, temporary relocation may be necessary. Relocation has been used in California during 24-hour work to repair earthquake-damaged highways, on one occasion in Utah on the I-15 project because of an individual’s medical problem, on the TRansportation EXpansion (T-REX) project in Denver, Colorado, during weekend demolition of nine bridges, and in Massachusetts for four apartments very close to the CA/T project. Temporary relocation usually involves assisting affected residents, including those who might be frail or elderly, to move into a hotel for a few days or weeks while excessively loud work is being completed. Vibration Similar to sound, vibration is fluctuating energy in motion, through solid media rather than air. Humans and animals can be sensitive to vibration, particularly in the low-frequency range of about 1 Hz to 100 Hz. Many types of construction activities cause vibrations that spread through the ground (ground-borne), most notably pile driving, hoe ram demolition, blasting, and vibratory com- pacting. Though the vibrations diminish in strength with distance from the source, they can produce annoying or objectionable audible and “feelable” levels in buildings very close to con- struction sites. Rarely do vibrations reach levels that cause structural damage to buildings. However, minor cosmetic damages can occur at lower vibration levels and, in the case of old, fragile, or historical buildings, a danger of significant structural damage always exists. Laboratory devices, such as electron microscopes and lasers, can be very sensitive to vibra- tions. Vibration displacement amplitudes of as little as 1 × 10-6 in. (1 micro-in.) can disrupt such sensitive equipment. Therefore, the area surrounding a construction site must be screened for research facilities, clinics, laboratories, and hospitals that might be using sensitive devices. Figure 4.6. Sample window treatment program eligibility policy (CA/T Project, Boston). The construction noise residential window treatment policy for the Central Artery/Tunnel (CA/T) project stated the following criteria to determine eligibility: • The resident must be subjected to nighttime (10 p.m. to 7 a.m.) construction noise • Other control methods (source and path) will not adequately mitigate the noise • The resident must be in close proximity to the construction work • The applicant must be a legal resident • Construction noise levels at the residence must be exceeding the project’s noise limits • Elevated noise levels are forecasted to exist consistently for a period in excess of two consecutive months • Situations must involve health condition, hardship, or severe impact (i.e., not financial means) • Mitigation is limited to bedroom windows, unless a relevant health condition is documented • There must be a written right-of-entry to authorize the work • The CA/T Environmental Panel must approve the treatment and associated cost

Nuisances 43 To control or limit project-caused vibrations, it may be necessary to place restraints on con- struction methods, allowable times, and equipment. However, the determination of acceptable vibration levels is very difficult because of its subjective nature with regard to being a nuisance. It is the unpredictability and unusual nature of vibration, more than the level itself, that is likely to result in complaints. The effect of intrusion tends to be psychological rather than physi- ological and is more of a problem at night when occupants of buildings expect no unusual dis- turbance from external sources. Vibration Sources and Strength Vibrations from construction work are normally the result of blasting, impact pile driving, hoe ram demolition, drilling, or the use of vibratory rollers. Construction vibrations are gener- ally assessed in terms of peak particle velocity (PPV) in units of in. per sec; however, they can also be expressed in vibration velocity decibel levels (VdB or Lv). PPV vibration data based on measurement of construction equipment and operations have been published, as shown in Table 4.5. The table shows average source levels under a wide vari- ety of construction activities. Resulting PPV levels measured or calculated at receptor locations, when compared against recommended criteria limits, can provide an indicator of the damage potential from the vibrations. Nevertheless, vibration levels below recommended criteria limits are not a guarantee that damage cannot occur or that complaints or claims will not result. When vibration levels from an “unusual source” exceed the human threshold of perception (PPV, 0.008–0.012 inches per second (in./sec)), complaints may occur. In an urban situation, serious complaints are probable when PPV exceeds 0.12 in./sec (New 1990). These levels are much less than what would result from slamming a door in a modern masonry building. People’s tolerance will be improved provided that the origin of the vibrations is known in advance and no damage results. A matrix of human response in relation to both blasting and earthquake motion is shown in Table 4.6. Note that humans are more sensitive to a blasting motion than an earthquake. The Federal Transit Administration (FTA) also provides guidance on acceptable levels of con- struction vibration (Hanson et al. 2006). Structural categories are defined in FTA guidelines on Table 4.5. Vibration levels for construction equipment and operations (Hanson et al. 2006). Equipment PPV at 25 ft (in./sec) Approximate Lv1 at 25 ft Pile driver (impact) upper range 1.518 112 typical 0.644 104 Pile driver (sonic) upper range 0.734 105 typical 0.170 93 Clam shovel drop (slurry wall) 0.202 94 Hydromill (slurry wall) in soil 0.008 66 in rock 0.017 75 Vibratory roller 0.210 94 Hoe ram 0.089 87 Large bulldozer 0.089 87 Caisson drilling 0.089 87 Loaded trucks 0.076 86 Jackhammer 0.035 79 Small dozer 0.003 58 1 RMS velocity in decibels (VdB) 1 micro-in./sec with an assumed crest factor (Peak/RMS) of x 4 (12 dB).

44 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity the basis of the sensitivity (or vulnerability) of buildings to major structural or minor cosmetic damages from vibration, as shown in Table 4.7. Major structural damages are seldom a concern from construction activities and only occur when a building is exposed to intense shock from events such as blasting or pile driving within a few feet. Minor cosmetic damages are typically more of a concern from construction activities and can manifest in cracking of wall or ceiling plaster, exacerbating spalling cracks in brickwork, and rattling/breaking of windows and other fragile objects. The criteria limits recommended by the FTA for avoidance of major or minor damages are expressed in units of PPV in in./sec. For major damages, a limit of 2.00 PPV is recommended. Different criteria limits, as shown in Table 4.7, are provided for minor cosmetic damages depend- ing on the receptor’s structural category and whether or not the source is transient (such as impact) or continuous in nature. Sensitive Equipment Vibration Criteria (VC) Curves Figure 4.7 shows a family of VC curves intended to protect sensitive devices from excessive vibration. These criteria originated with the Institute of Environmental Sciences and Technology (IEST) and were published in its Standards RP-CC012.2 and RP-CC024. The FTA subsequently adopted and recommended these criteria as well in their Transit Noise and Vibration Impact Assessment Manual (Hanson et al. 2006). The FTA manual only shows VC curves down to VC-E (125 micro-in./sec or 42 VdB); however, the curves can be extended to lower VC-F and VC-G ranges. In general, each lower VC curve represents half the vibration velocity level of the one above it. The VC curves elbow upward at and below the 8 Hz third-octave band; however, they should be extended linearly (flat) for particularly-sensitive devices whose mounting systems are not fully understood. Table 4.8 provides the vibration velocity levels for each VC curve expressed in engineering units and decibels, and a description for the intended use of each criterion curve. Table 4.6. Human response to motion (Oriard 1989). Human Response Earthquake (PPV in./sec) Blasting (PPV in./sec) Barely perceptible 0.26–0.80 0.01–0.10 Distinctly perceptible 0.46–1.40 0.05–0.50 Strongly perceptible 1.50–5.70 0.50–5.00 Table 4.7. Federal Transit Administration construction vibration guidance (Hanson et al. 2006). Building Category PPV (in./sec) Approximate Lv1 I. Reinforced-concrete, steel, or timber (no plaster) 0.50 102 II. Engineered concrete and masonry (no plaster) 0.30 98 III. Non-engineered timber and masonry buildings 0.20 94 IV. Buildings extremely susceptible to vibration damage 0.12 90 1 RMS velocity in decibels (VdB) 1 micro-in./sec with an assumed crest factor (Peak/RMS) of x4 (12 dB).

Nuisances 45 Figure 4.7. Impact assessment VC curves (Hanson et al. 2006). Table 4.8. VC limits and intended use (Hanson et al. 2006). VC Curve Name Vibration Limit Intended Use Micro- in./sec VdB VC-A 2,000 66 Adequate for medium- to high-power optical microscopes (400X), microbalances, optical balances, and similar specialized equipment VC-B 1,000 60 Adequate for high-power optical microscopes (1000X), inspection, and lithography equipment to three-micron line widths VC-C 500 54 Appropriate for most lithography and inspection equipment to one-micron detail size VC-D 250 48 Suitable in most instances for the most demanding equipment, including electron microscopes operating to the limits of their capability VC-E 125 42 The most demanding criterion for extremely sensitive equipment

46 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity Vibration Mitigation The mitigation techniques for decreasing vibration impacts are similar to those used to lessen noise nuisances. The following are the questions to address concerning vibrations: • Will construction operations cause vibrations? • Are sensitive populaces, buildings, structures, or laboratory equipment in the vicinity? • Can site-specific trials be conducted to assess possible damage/intrusion? Answering these questions requires a clear understanding of construction equipment location and construction processes in relation to critical receptors. Tip If the goal is to mitigate complaints, even from simply noticeable vibrations, the zone of concern can be as great as 1,300 ft. Key Take-Away If Damage/Intrusion is Possible, Modify Design and/or Construction Method The basic approach with regard to contract specification control of vibration is the imposition of a limiting value for vibration. This is usually in terms of a resultant PPV at a specified distance or at a critical structure. Such a specified VC results in a sharing of risk with the contractor, so pre-construction photographic surveys should be conducted to document the buildings’ exist- ing conditions. Specifications and Design Establishing limitations on blasting and pile driving vibrations can be done by project speci- fication. For example, impact pile driving can be replaced with hydraulic push piles, drilled cais- sons, or slurry walls; or blasting can be replaced with rock drilling and splitting. Typically, these alternate methods take more time and may cost more to accomplish, but they are available if/ when vibration damages must be avoided. In addition, specifications can be used to control vibration nuisance risks as outlined in Table 4.9. Resource The principal means of mitigating vibration problems, as reported by STAs, pile driving con- tractors, and engineering consultants, can be found in NCHRP Synthesis of Highway Practice 253: Table 4.9. Effective vibration control specifications. Category Control Directives by Specification Project layout and access Route heavily loaded trucks away from residential streets. Establish designated haul routes so that the fewest possible residences are affected. Create project work zones that control the placement of operating equipment on the construction site so that equipment is kept as far as possible from vibration-sensitive receptors. Sequence of operations Phase demolition, earthmoving, and ground-impacting operations so they do not occur concurrently. Community outreach Whenever possible, perform high-vibration tasks at the least objectionable times of day as determined through dialog with the affected public. Work hour restrictions Limit vibration-causing activities to daytime hours, or daytime and evening hours only. People are more aware of vibration in their dwellings during late night and early morning hours. Alternative construction methods Drilled piles or the use of a hydraulic pushed or vibratory pile driver causes lower vibration levels where the geological conditions permit their use. Avoid impact pile driving whenever possible in vibration-sensitive areas.

Nuisances 47 Dynamic Effects of Pile Installations on Adjacent Structures. TRB, National Research Council, Washington, D.C. (Woods 1997). Key Take-Away Vibrations typically do not occur at the same moment; therefore, the single highest vibration- producing source will create the critical PPV level. Dust During the night, many households leave their windows open to take advantage of the cool night air. With urban nighttime construction projects being very close to people’s living space, dust can be a problem. Nighttime construction dust problems are accentuated by the lighting, which makes the par- ticulate matter very visible. Fugitive dust may be generated by construction operations, and the contract specifications should require that the contractor prepare a dust control plan. In many cases, dust control is not a problem that is limited to nighttime activities; therefore, air quality/dust control plans should be for all hours of the day or night. Specific areas that dust control plans should address are outlined in Table 4.10. Summary Good construction noise, vibration, and dust control specifications are effective tools in miti- gating the adverse and objectionable impacts of construction on abutting communities. The primary goal with potential nighttime construction nuisances is to minimize the impact of construction noise at night when people are most sensitive. The mechanisms to achieve that goal vary from contract to contract because of area-specific conditions, the type of construction, the inherent noise reduction qualities or sensitivity of affected receptor structures, the desires of the affected abutters, and the cost and schedule implications of mitigation. In addition, it may be necessary to have specific noise mitigation measures specified for certain work. Table 4.10. Dust control mitigation strategies by category (Schexnayder and Ernzen 1999). Category Countermeasures Earthwork Watering, pre-wet sites Disturbed surface areas Watering, chemical stabilizers, wind fences, wind screens, berms, stabilization with vegetation or gravel Open storage stockpiles Watering, chemical stabilizers, wind fences, wind screens, berms, coverings, enclosures Unpaved roads Watering, chemical stabilizers, stabilization with gravel, restrict vehicle speed Paved road track out Limit or restrict access; stabilized, gravel, or paved construction entrance pad; wheel-wash station; vacuum/wet-broom public roadway Hauling Maintain minimum freeboard, tarp Demolition Watering, pre-wetting Work limits during high winds Cease work temporarily on hot dry nights or for certain wind directions