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8 consistent with human hearing [by reducing the contri- In addition to establishing these noise measurement tools, bution of lower and very high frequencies to the total FAR Part 150 established a program for airports to develop level) [14 C.F.R. Pt 150, App A A150.3(a)]. (1) a "noise exposure map" or NEM that models existing and For purposes of evaluating noise exposure, the FAA future noise exposure and identifies the areas of incompatible selected the DayNight Average Sound Level (DNL), the land use, and (2) a "noise compatibility program" or NCP that 24-hour average sound level, in decibels, for the period identifies, examines, and recommends to the FAA alternative from midnight to midnight, obtained after the addition means to mitigate and abate noise [49 U.S.C 47503 (noise of ten decibels to sound levels for the periods between exposure maps) and 47504 (noise compatibility programs); midnight and 7 a.m., and between 10 p.m. and mid- 14 C.F.R. Pt. 150]. night, local time. The symbol for DNL is Ldn [14 C.F.R. Pt 150, App A A150.3(b)]. The NCP often is a principal component of an airport's With respect to land use compatibility, the FAA pub- overall noise program since the NCP (1) is intended to be com- lished a table in its regulations (14 C.F.R. Part 150, prehensive, both in its evaluation of noise issues and potential Appendix A), which prescribes whether a variety of dif- solutions, (2) presents an opportunity for community involve- ferent land use categories are compatible with aircraft ment and input, and (3) provides an indication of which noise operations for a particular range of noise levels (14 control measures are eligible for federal funding. C.F.R. Pt 150, App A Table 1). That table identifies DNL 65 dB as the threshold of compatibility for most Part 150 identifies certain measures that should be consid- residential land uses, and where measures to achieve ered in preparing the noise compatibility program; these are outdoor to indoor Noise Level Reduction of at least 25 summarized in Table 2. dB and 30 dB should be incorporated into building codes and be considered in individual approvals. POLICIES ADDRESSING NOISE OUTSIDE DNL 65 Each of these requirements has been the subject of confu- sion and contention. For example, there have been complaints Aircraft noise and land use compatibility has long been recog- that dB(A) fails to account for low frequency noise (experi- nized as an important consideration in planning of communi- enced as vibration or rumble) often associated with jet opera- ties and the airports that serve these communities (President's tions. The primary complaint with DNL is that it does not Airport Commission May 1952). The quantitative approach to reflect the sound of individual aircraft operations, which may determining land uses compatible with aircraft noise began be dramatically louder than the steady rate of sound captured with the Noise Control Act of 1972. It required the U.S. EPA by DNL. In addition, although some contend that the DNL Administrator to conduct a study of the " . . . implications of 65 dB level represents a scientifically and statistically accurate identifying and achieving levels of cumulative noise exposure predictor of community annoyance, others assert that it is a around airports . . . " (U.S. EPA 1973). This requirement poor predictor of how a particular community or an individual resulted in the identification of DNL as the measure of cumu- responds to aircraft noise. lative noise, and DNL 60 dB as the threshold of compatibility; TABLE 2 NOISE COMPATIBILITY PROGRAM MEASURES Operational Measures Land Use Measures Program Management Measures Implementing a preferential Acquiring noise-impacted property Posting signs on the airfield and at runway system to direct air traffic Acquiring "avigation easements" or other other locations at the airport to notify over less-populated areas interests in property that permit aircraft to pilots about recommended flight pro- Using flight procedures, including fly over the property in exchange for pay- cedures and other measures noise abatement approach and ments or other consideration Creating a noise office at the airport departure procedures Requiring disclosure about the presence of and/or assigning responsibility for Identifying flight tracks to reduce the airport and potential noise impacts in noise issues to a staff member noise and/or direct air traffic over real estate documents Creating a dedicated telephone line or less-populated areas Constructing berms or other noise barriers other means for neighbors to submit Adopting mandatory restrictions Sound insulation of structures used for comments/complaints about the air- based on aircraft noise characteristics, noise-sensitive land uses (e.g., residences, port and individual aircraft operations such as curfews schools, nursing homes) Making flight track information avail- Identifying a particular area of the Requiring the use of sound insulating able to the public airport that can be used for aircraft building materials in new construction Developing educational materials engine runups and constructing a Imposing zoning or other controls on noise- about the airport's noise program for "ground runup enclosure" to reduce sensitive land uses in impacted areas, pilots, other airport users, and commu- noise from runups including prohibiting such development or nity members requiring special permits and approvals

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9 below this level, there should be limited annoyance and min- 14 CFR Part 150. In this regulation, the FAA provided a table imal complaints about aircraft noise. This report (U.S. EPA giving various land uses compatible with DayNight Average 1973) provides extensive discussion of why DNL was chosen Sound Levels. This table shows that residential uses are con- and why DNL 60 dB was identified as the appropriate limit sidered compatible with levels below DNL 65 dB. Most Part of exposure. The discussion focuses on effects on people and 150 studies result in identification of noise abatement measures communities, including hearing, interference with speech, (e.g., changes in flight operations, and runway use) and/or noise sleep and learning/thinking, annoyance, and complaints, and mitigation measures (commonly sound insulation). Through provides some information on nonauditory health effects. fiscal year 2006, the FAA has provided more than $7.5B for implementation of these measures (FAA 2008). The FAA also The Noise Control Act of 1972 also required the EPA uses DNL and specific computation procedures for its calcula- Administrator to publish " . . . information on the levels of tion to comply with the National Environmental Policy Act environmental noise the attainment and maintenance of which (NEPA) (FAA Orders 1050, 1E and 5050.4B) and for guiding in defined areas under various conditions are requisite to pro- the funding of projects associated with the Airport Improve- tect the public health and welfare with an adequate margin of ment Program (AIP) (FAA Order 5100.38C). safety." This requirement resulted in what is now commonly referred to as "The Levels Document," (U.S. EPA 1974). This A few states and many local jurisdictions have recom- report recommended that to provide this protection, the value mended DNL values identical to those of FAA for land use of the DayNight Level not exceed 55 dB. compatibility with aircraft noise, though some also identify dimensions of a "noise sensitivity zone" (Minnesota, Ore- Next, the state of Maryland passed the Maryland Envi- gon). Several jurisdictions have used DNL 60 in defining ronmental Noise Act of 1974. This legislation included the planning objectives or goals (Coffman Associates 2000). requirement that the Maryland Department of Transportation Limits are provided as guidance (Wisconsin, Oregon), and (DOT), State Aviation Administration select the noise analy- may include zoning ordinances and planning templates (Ore- sis method and exposure limits. In its report Selection of Air- gon). Other states, notably California and Maryland, have set port Noise Analysis Method and Exposure Limits (1975), specific procedures that must be followed in examining air- Maryland set DNL 65 dB as its official noise limit for residen- port or aircraft noise. The Department of Defense also pro- tial land use effective 1 July 1975, and DNL 60 dB when the vides similar DNL-based levels for determining Air Installa- "U.S. Fleet Noise Level is reduced 5dB below 1 July 1975 tions Compatible Use Zones (1977), which incorporate noise level." In discussing the selection of the compatibility DNL and accident potential in setting the size and shape of the level, the report noted that neither Congress nor the EPA zones. Further, the department will provide funding and guid- intended to set limits for states and local jurisdictions. "This is ance to a community that wishes to develop a plan for setting a decision that the Noise Control Act clearly leaves to the in place land use compatibility measures around military air states and localities themselves." Maryland's policy is notable installations, but generally provides no funding to implement because it has often been described as one of the models for those measures (Joint Land Use Study . . . 2002). the later Part 150. The FAA has rarely funded land use programs outside Federal policy for civil aviation noise is described in the DNL 65 in order to focus on airports with significant (as FAA's 1976 Aviation Noise Policy, which included a goal of defined by DNL 65) or severe (as defined by DNL 75) noise "confining severe aircraft noise exposure levels around U.S. exposure. As the existing noise mitigation programs mature airports to the areas included within the airport boundary or at airports, and with increasing numbers of operations by over which the airport has a legal interest, and of reducing sub- quiet aircraft, the proportion of citizens outside the DNL 65 stantially the number and extent of areas receiving noise expo- complaining about aircraft noise has increased. Today, noise sure levels that interfere with human activity" (FAA 1976). offices at many airports have an increasing workload to The DOT policy recommended use of the Noise Exposure respond to these complaints. Furthermore, in some locations, Forecast (NEF) metric and stated that "severe" aircraft noise approval of airport capacity improvements has been contin- occurred at levels of 40 NEF or more, and "significant" aircraft gent on the ability to address noise/land use conflicts outside noise occurred at levels of 30 NEF or more. The policy further DNL 65. identified NEF 30 and 40 as equivalent to DNL 65 and 75, respectively. The policy also stated that "the objective of the A requirement of Vision 100 (Public Law 108-176) pre- airport noise plan should be to develop noise reduction tech- vented the FAA from issuing AIP funding under Part 150 for niques that to the extent possible would confine the area land use compatibility actions outside the DNL 65 noise con- exposed to this level of noise to the airport boundary or land tour from 2004 through 2007. Although the provision has actually being used or which can reasonably be expected to be sunset, there continues to be opposition to funding of such used in a way compatible with these noise levels." action ("ATA Says Block-Rounding at Bob Hope, Ft. Laud- erdale Int'l Has Gone Too Far" 2008). In some instances, this In 1984, the FAA adopted the final rule that set out the provision also resulted in FAA's refusal to adopt noise abate- process for noise compatibility planning around airports-- ment flight procedures if such procedures were directed at