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EFFECTS OF AIRCRAFT NOISE: RESEARCH UPDATE ON SELECTED TOPICS SUMMARY In the years since Aviation Noise Effects (FAA Report No. FAA-EE-85-2) was published in 1985, much has changed in the aviation world. Quieter jets, increased air travel, new breeds of aircraft types, increased awareness of proper land-use planning, and mitigation of previously incompatible land uses are just a few of the changes. Our knowledge of the effects of aviation noise has also changed. The greatest increases in knowledge are in the areas of health effects, annoyance, sleep disturbance, and potential effects on children's learning abilities in schools. This document is intended to update and complement the original document, primarily by focusing on the latest research efforts and conclusions. Considerable research, review of previous research with new thought, new independent research, and collaborative efforts have been compiled in this report. Although we have progressed in many areas, there is still much to be learned. This synthesis provides a condensed review of selected research, with detailed discussions appearing in Appendix A, which the reader is highly encouraged to review thoroughly. Chapter One--Introduction and Methodology After a complete review of FAA's 1985 Aviation Noise Effects report, a literature search was undertaken, with representative studies completed since 1985 being selected, annotated, and categorized for each of the 11 chapter topic areas outlined. For ease of use, each chapter has its own discussion and summary, and is immediately followed by an annotated bibliography. Chapter Two--Health Effects of Aviation Noise In the 20-plus years since publication of the FAA's Aviation Noise Effects, considerable research, review of previous research with new thought, and new independent research, as well as collaborative efforts to identify health effects related to aviation noise, have been com- pleted. Some studies have identified a potential correlation between aviation or road noise above certain noise thresholds, typically a daynight average noise level (DNL) value of 70 dBA, and increased hypertension; however, other studies contradict such findings. Occu- pational noise is also an intricate concern. Health effects on children, particularly those with decreased cognitive abilities, mental disturbances, or other psychological stressors, and studies of pregnancy and low infant birth weights, all indicate either little correlation or conflicting results of relationships between aviation noise and childhood psychiatric disorders, environ- mental factors, or low infant birth weights. Additionally, recent studies conclude that aviation noise does not pose a risk factor for child or teenage hearing loss. Because aviation and typical community noise levels near airports are not comparable to the occupational or recreational noise exposures associated with hearing loss, hearing impairment resulting from community aviation noise has not been identified. However, newer studies suggest there may be a potential relationship between aviation noise levels and hypertension or ischemic heart dis- ease at noise levels as low as 50 dBA Leq. Despite decades of research, including review of old data and multiple new research efforts, health effects of aviation noise continue to be complicated and the need for additional

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2 research is crucial to understanding. This synthesis report includes annotation of 21 recent reports on health and hearing. Chapter Three--Annoyance and Aviation Noise Annoyance remains the single most significant effect associated with aviation noise. Community annoyance is the aggregate community response to long-term, steady-state exposure conditions. However, to adequately support government noise policy-making efforts, it is necessary to synthesize the large amount of data contained in journal articles and technical reports to develop a useful exposure-response relationship. Significant research has occurred since the 1985 aviation effects report was published. There is no current research to suggest that there is a better metric than DNL to relate to annoyance. However, there remains significant controversy over the use of the dose-response annoyance curve first developed by Schultz and then updated by others. Although the curve is presented as a smooth definitive relationship between DNL and annoyance, there is an extraordinary amount of scatter in the data used to develop the curve. Investigations that report a distinct percentage of the population that will be highly annoyed at a given DNL may incorrectly be interpreted as having a more precise meaning than should be assumed from the data, given such a large amount of scatter. Furthermore, more recent research tends to support the idea that the dose-response curves are different for aircraft, road, and rail noise sources. An area of research that remains to be investigated is the relationship between single-event noise levels and annoyance. The expanding use of airport noise monitoring systems, flight tracking systems, and geographic information systems (GIS) may make the evaluation of annoyance and single-event noise a prime area for examination. This synthesis report includes annotation of 12 recent reports on annoyance and aviation noise. Chapter Four--Sleep Disturbance and Aviation Noise Sleep disturbance is a common effect described by most noise-exposed populations and their complaints are often very strong, especially in the vicinity of airports. Protection of a particular sleep period is necessary for overall quality of life. Sleep may be quite sensitive to environmental factors, especially noise, because external stimuli are still processed by the sleeper sensory functions, although there may be no conscious perception of their presence. The large amount of research published during the last 30 years has produced considerable variability of results, some of which is controversial. As in establishing the health effect of aviation noise, the absence of one internationally accepted "exposure-effect" or "dose- response" relationship is largely the result of the lack of one obvious "best choice" research methodology, as well as the complex interactions of the many factors that influence sleep disturbance. These include the differences of the noise source and the context of the liv- ing environment, to name one example. Current exposure-response relationships use either "awakenings" or "body movements" to describe sleep disturbance. Although the most common metrics for assessing the impacts of community noise, DNL, and Day-Evening-Night Average Sound Level (Lden or CNEL), already contain a 10-dB penalty for nighttime noises, there are circumstances where a separate analysis of the impacts of nighttime transportation noise is warranted. There are, however, different definitions of sleep disturbance and different ways to measure it, different exposure metrics that can be used, and consistent differences in the results of laboratory versus field studies. At the present time, very little is known about how, why, and how often people are awakened during the night, although it is generally acknowledged that the "meaning of the sound" to the individual, such as a child crying, is a strong predictor of awakening. Although the Integrated Noise Model can estimate the various metrics referenced in this discussion of sleep disturbance, there is sub- stantial controversy associated with how to apply and interpret these studies.

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3 Since 1985, research has focused on measuring in-home sleep disturbance using techniques not available before that time. A review of in-home sleep disturbance studies has clearly shown that it requires more noise to cause awakenings than was originally thought based on laboratory sleep disturbance studies. In the context of attempting to estimate the population awakened for a specific airport environment, or the difference in population awakened for a given change in an airport environment, the sleep disturbance research may not yet have sufficient specificity to warrant such an estimate. This synthesis report includes annotation of 14 recent reports on sleep disturbance and aviation noise. Chapter Five--Speech Interference and Aviation Noise Speech interference (SI) is an important component in annoyance response. SI has been well researched over the years and there have been few new research papers dealing specifically with aircraft noise published on this topic since 1985. However, most SI studies and guidelines deal with steady-state noises. Aircraft noise, however, is an intermittent noise, and therefore the SI literature is inadequate with respect to intermittent noise (the 1974 EPA levels document briefly addresses the issue of intermittent noise). There is a need for more research on the effect of intermittent noise, such as an aircraft flyover, on speech. This synthesis report includes annotation of four recent reports on SI and aviation noise. Chapter Six--Effects of Aviation Noise on Schools The research on the effects of aviation noise on schools has focused on identifying noise as an important issue in the classroom. However, there has been little work done on establishing a dose-response relationship between aviation noise and classroom effects. This lack of a reliable dose-response relationship between aircraft noise and classroom effects makes the evaluation of aircraft noise on schools and setting policy very difficult. Although it is clear that at high enough noise levels speech communication is virtually impossible, there is no clear threshold for when aircraft noise begins to effect schools. Much of the research has focused on the use of standardized test scores and stress hormone measurement in cross-sectional studies. There is a clear need for additional research on the effects of aviation noise on schools and these studies need to include in-classroom noise measurements and observation of student responses to aircraft activity. This synthesis report includes annotation of 13 recent reports on aviation noise and schools. Chapter Seven--Effects of Aviation Noise on Parks, Open Space, and Wilderness Areas National parks have been a focus of park and open space noise research in the United States. Preserving the natural quiet is a controversial topic, one that is subject to Congres- sional mandate. The FAA has developed specific analytical tools included as part of the most recent version of the Integrated Noise Model for use in analyzing aviation noise affects in national parks. Little research has been done on the effect of aviation, or any other kinds of noise, on the more common urban and suburban parks. The research on urban parks that has been done in Europe indicates that users consider noise a very important factor in park enjoyment, but that park users judge sounds differently based on whether the noise is an expected or unexpected part of the park environment. This synthesis report includes annota- tion of nine recent reports on aviation noise and parks, open space, and wilderness. Chapter Eight--Aviation Low-Frequency Noise and Vibration Low frequency noise is an issue for observers located near an airport runway where jet noise at the start of takeoff roll and/or the thrust reversers may cause low frequency noise impacts not common to other parts of the airport environs. Low frequency noise is unique in that it may not be adequately described by the A-weighted decibel, and may cause structural

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4 vibration that could lead to increased annoyance owing to the rattling of windows or bric- a-brac on shelves or hanging on walls. Low frequency noise studies have proven to be controversial and ongoing research is attempting to address the low frequency noise issues. Among the outstanding issues are what metrics to use to describe low frequency noise and what noise levels are compatible with residential land uses. This synthesis report includes annotation of eight recent reports on aviation low frequency noise and vibration. Chapter Nine--Aviation Noise Effects on Wildlife and Domestic Animals The effects of aviation noise on animals have been studied rather extensively over the past 20 years, with much of the work being conducted by U.S. Air Force-sponsored re- searchers. The studies have revealed that the effects are highly species-dependent and that the degree of the effect may vary widely. Responses of animals to aircraft noise vary from almost no reaction to virtually no tolerance of the sound. The question of how adaptable animals are remains largely unanswered. Both wild and domesticated animals have been studied, although more research has centered on domesticated or laboratory animals (such as rats and mice). Although noise is often defined as unwanted sound for humans, it has been suggested that it is also so for animals. "Noise" is best defined as any sound that (1) causes hearing loss; (2) masks signals needed for communication, navigation, prey detection, predator avoidance, and environmental monitoring; (3) effects non-auditory health; (4) effects biologically significant changes in behavior; and (5) alters population including declines in abundance, changes in distribution, or reproductive failures. Although it is not possible to generalize a dose-response relationship for all wildlife and farm animals, the reader is referred to specific tables in chapter nine for a summary of the findings of effects of aircraft noise and sonic booms. Of noteworthy reference is the National Park Service's comprehensive annotated bibliography, "Impacts and Noise and Overflights on Wildlife," published in 2005. The report also includes 76 documents divided into categories. Although it is impossible to generalize or summarize the results of such a broad range of studies in this synthesis, it is clear that some reports found dramatic effects, whereas others discovered that other factors overwhelm the noise effects. This synthesis report includes annotation of six recent reports on aviation noise and wildlife and domestic animals. Chapter Ten--Aviation Noise Effects on Property Values The studies of the effects of aviation noise on property values are highly complex owing to the differences in methodologies, airport and community environments, market condi- tions, and demand variables involved. Whereas most studies concluded that aviation noise effects on property value range from some negative impacts to significant negative impacts, some studies combined airport noise and proximity and concluded that the net effect on property value was positive. Prospective homebuyers were at times not well-informed about the noise levels of aircraft operations near the property of interest. Lacking information often led to high bid prices and possible disappointment after purchase. However, once noise levels stabilized, the next homeowner was compensated once the property value adjusted as the result of the effects of noise. Lastly, the technology available to analyze data has improved throughout the years. The spatial nature of aircraft operations, noise contours, and property location will continue to prompt studies founded in geographic information system analysis that will improve our understanding of the effects of aviation noise on property value. This synthesis report includes annotation of 12 recent reports on aviation noise and property values. Chapter Eleven--Effect of Meteorology on Aviation Noise

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5 Meteorology plays a very important role in the propagation of sound. Simply put, air absorbs sound. As sound travels through the atmosphere it is attenuated by this absorption. Complicating matters is that air absorption varies with temperature and humidity and the frequency of the sound. Sound travels downwind better than upwind. In the real atmosphere the temperature, humidity, and wind speed and direction are not homogeneous, but are chang- ing constantly. Temperature and/or wind gradients cause refraction (bending) of sound waves. One of the consequences of the complex way weather affects sound propagation is that noise models are limited to estimating noise levels for average conditions. Comparing noise model predictions with short-term noise measurements is meaningless, as atmospheric effects are not adequately accounted for in the model. However, long-term measurements will produce an average noise level in which atmospheric effects will tend to average out and comparison with noise model results will be much more meaningful. This caution should be noted for any short-term measurement program. Current research includes highly technically complex studies analyzing how sound levels increase as the refractive curvature goes from negative to positive values; ground effects on propagation and infrasound propagation. Research indicates that large-scale turbulence is a significant cause of acoustic signal fluctuations, particularly in the signal phase. Other, more site-specific research evaluates the influence of a pine forest on sound propagation, finding high frequency attenuation owing to the forest that increases with distance. This synthesis report includes annotation of seven recent reports on meteorology and aviation noise. Chapter Twelve--Effect of Topography and Ground Absorption on Aviation Noise Aircraft sound heard by an observer can be influenced by a number of factors. As previously stated, meteorology is one such factor. Another factor is the propagation of sound over the ground and as affected by terrain. When an aircraft is directly overhead, the sound experienced by an observer is only affected by meteorology. However, as the aircraft passes by or is at lower elevation angles, the sound heard by an observer is both the sound that travels in a straight line from the aircraft plus the sound reflected off the ground. Although the interaction of sound traveling over the ground is quite complex, recent research has provided new insight. Although FHWA's 1978 report on highway noise prediction model was prepared before 1985, it still presents one of the best descriptions of how to include noise barrier effects in transportation modeling. It includes detailed methodologies to computer noise barrier effects. This synthesis report includes annotation of seven recent reports on topography, ground absorption, and aviation noise.