Introduction
The noise that aircrafts produce continues to be a pertinent issue at numerous airports, particularly, at the point whereby there is a consideration of or an execution of expansions. In the United States, the enactment of various procedures for the reduction of airport noise exposure has taken place. These procedures and strategies include operational requirements, the use of quieter aircrafts, the soundproofing of airports and the purchase of surrounding residential properties, among others. As a result of these mitigation efforts, over the past twenty-five years, have resulted in a tangible decline in the number of individuals exposed to significant levels of noise, roughly estimated to be 65 decibels (dB) or higher. Conversely, as of the beginning of the year 2000, the entire commercial fleet of American aircrafts was converted to stage three aircraft levels. This conversion brought in itself further noise levels mitigations leading aircrafts to require contemporary technologies in dealing with the stipulations. Therefore, this paper focuses on the effects of aircraft noise on the surrounding residential properties, particularly, their price value. Moreover, since higher noise levels present environmental challenges, this paper analyzes its effects on residents living adjacent to airports with a focus on children and their developmental process.
Statement of the Problem
A simple definition of noise states that it is an unpleasant or unwanted sound (Nelson, 2004). The most conjoint effects related to noises produced by aircrafts are learning and speech interference, annoyance, and disturbances in sleep. Sequentially, these effects continue up to the point whereby they interrupt the daily activities of life such as the viewing of television, normal conversations, overall productivity, schoolwork, recreations while outdoors in the case of children, and apposite family activities. Therefore, in essence, annoyance is an adverse psychological response to noise exposure, including the apprehension or anxiety that may result from the exposure to noise. Noise transpires in divergent levels, and at degrees that are above 75 dB, the Environmental Protection Agency (EPA) warns that adverse health effects may occur in a significant amount of the population, which may include hearing loss. Moreover, persons who appear to spend more time indoors are at a greater threat, and this includes young children, aged individuals in warmer climates and persons who have certain outdoor occupations. This phenomenon makes aircraft noise a pertinent environmental issue that needs immediate awareness and applicable mitigation measures.
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In understanding the relationship between the problem of hedonic property value and noise annoyance, consider two residential properties. These two properties are identical in all respects regarding size, materials used in building, among other variables except for one fact: one is located close or under the flight path of an aircraft, while the other is not. In the former’s case, the analysis indicates that its market value will be lower than that of the latter. This takes place since potential buyers significantly reduce the petition for the first house compared to the second, indicative of a present actual value that is discounted owing to relatable variables such as annoyance, the development of possible side effects, the loss of tranquility, among others. Therefore, the measure of non-induced damages reflects the innate metamorphosis between the values of the two houses, which are in essence market determined. As such, this analysis can be extended to further analyze different noise exposure levels since annoyance, and other noise effects rise predictability with an increase in the levels of exposure. This results in the fact that when there is a missing market for tranquility, another corresponding market transpires wherein persons are willing to pay heftily to avoid various levels of exposures to aircraft noises. Such willingness to pay for quietude unbundles complex products in property values leading to hedonic price ranges (Espey, 2000).
Moreover, a huge problem arises from the incessant noises produced by aircrafts in relation to the health of residents living close to major commercial airports; predominantly, among children. Research by Black, Black, Issarayangyun & Samuels (2007), conducted through cross-sectional studies of residential neighborhoods adjacent to Sydney Airport, indicate that subjects chronically exposed to significant aircraft noise levels are more likely to develop hypertension and stress compared to those not exposed to these levels. Further, the research describes major policy implications and noise management regulations and policies within commercial airports in a bid to determine the stipulated noise level requirements and mitigation measures. As a result, while major airports continue to effect appropriate rules and regulations, the underlying problem of noise disturbances in nearby commercial areas persists and continues to bear a significant effect on individuals and surrounding property values. Among children, longitudinal and cross-sectional data continues to indicate the effect of aircraft noise on schoolchildren in their elementary stages, and this translates to the effects of community noise on their behavior (Cohen et al., 1981). In school children, overexposure to varying noise levels leads to divergent issues such as increased blood pressure, distractibility, helplessness, and poor school achievements among others. Through data from attrition samples, analysis corroborates the fact that prolonged exposure to intense noise levels such as aircraft engines results in debilitating effects on the health of those exposed.
Background of the Problem
As one of the largest contributors to community noise, transportation continues to affect various individuals in dissimilar ways. Moreover, as noise levels increase from detectable, it affects people in various ways and becomes increasingly annoying at the same time. Therefore, knowing the sources of noise plays a momentous role in the determination of community responses: a good example being the three dissimilar noises in transportation, which are road-traffic, aircraft and rail noises. These are often rated differently as per the normalcy in the A-weighted Sound Pressure Level (More, 2010). Further, from different empirical field studies, the same average A-weighted sound pressure levels in noises that emanate from aircrafts represent a higher level compared to those noises that originate from other sources such as rail and road traffic. This incident makes noises that emanate from aircrafts incessant and displeasing. This difference has the description of being an “aircraft malus.” According to the ISO 1996-1:2003, the provision of a 3 dB penalty for aircraft noise and a 6 dB bonus for trains while examining the effect of aircraft and train noise respectively, is indicative of non-acoustic issues in the operation of aircrafts such as the fear of crashing and the loss of privacy (More, 2010).
Noises produced by aircrafts during their flyover, landing and taking off operations causes increased community annoyance. Broadly defined, annoyance pertains to a psychological or physical discomfort resultant from noises or interferences from divergent activities. As such, aircraft noise has the consideration of being an annoyance, predominantly, when it interferes with daily activities such as day-to-day communications, cognitive capabilities, learning activities in classrooms, as mentioned earlier. At higher noise levels, such annoyance leads to not only hearing damages but also the exposition to risk factors that lead to a continual effect on various bodily faculties such as respiration, digestion, the mental state among others. Further studies indicate that continual exposure to persistent noise levels leads to the development of depression and nervousness. Due to the numerous incidences of psychological and physical discomforts in the levels of aircraft noises, airports continue to be the greatest environmental pollution problems seen in the contemporary world. Presently, the Federal Aviation Administration (FAA) uses the Day-Night Average A-weighted Sound Pressure Level (DNL), to quantify efficiently, the noises that come from aircrafts and their potential to induce annoyance among the communities that live around the airports. Similarly, other organizations employ the use of DNL annoyance levels, which indicate that airports are highly stressful environments. Such organizations include the Department of Housing and Urban Development (HUD), the Federal Railroad Administration (FRA), the Federal Transit Administration (FTA), the Surface Transportation Board (STB), the National Research Council (NRC), and the US Environmental Protection Agency (USEPA) (More, 2010).
Within aviation, the noise generated by the flight of aircrafts is quite complicated. The sources of sound are described in four major categories. These categories include the jet noises, the combustor noise, the turbomachinery noise, and the aerodynamic noise. The jet noises comprise a mixture of high-velocity exhaust gases with ambient air. The combustor noise comprises of the noises associated with the drastic oxidation of the jet fuel and the resultant energy propagation. The turbomachinery noise is often noticed through the approach of an aircraft, while the aerodynamic noise comes from rapid movements of air through the craft’s surface. While contemporary technologies have significantly reduced the production of noises about the jet noise and combustor noise, the turbomachinery noise is still a constant issue, and aerodynamic noise reduction is still in its infancy of research and in-depth studies. Therefore, as the jet and combustor noises are reduced significantly, the aerodynamic noise is still a pertinent issue and a source of discomfort for future aircraft developments. Moreover, while noise propagation varies according to various variables such as atmospheric absorption, wave divergence, ground attenuation, among others, the noises propagated by aircrafts continue to be a big issue. In essence, sound waves permeating from a source in an undisturbed manner an in a homogenous nature travels in waves that are spherical in nature. While the sound travels, a dissipation occurs; however, the resultant spread ensures that sound travels in a wider geographical location resulting in constant spread leading to massive noise pollution.
Although there is present uncertainty in the forecast for increased growth projections in air travel, empirical studies continue to show an increase in exposed populations. Since noise is the foremost environmental apprehension at high capacity airports, according to the Federal Aviation Administration (FAA) 47 percent of transfer airports and 75 percent of colossal airports continue to build and propose contemporary runways. Additionally, in such airports with these characteristics, the capacity to expand is often decelerated by major public concerns of noise exposure. As a result, the measurement of the economic value of quietude fundamentally focuses on the effects of substantial exposure to noise on the value of residential property. Thus, through the application of hedonic price analysis, quite a number of studies have analyzed this pertinent value empirically, focusing on airports located in Canada, Australia, Netherlands, the United States, the United Kingdom, and other countries as well. Over time, models of hedonic price continue their application to effect numerous dis-amenities and amenities in relation to the value of residential housing. Such models continue to show and use the various differentiations that exist in the markets of housing, in terms of characteristics and locational attributes relating to a sample of properties. Besides, the model becomes useful while there exists a localization of the attribute in question.
To comprehend hedonic pricing better, take for example the noise that emanates from major highways or airports adjacent to prime properties. Noise from these utilities affects such properties while at the same time leaving unaffected a wide-ranging urbanized area. In such a case, the hedonic price of the variable identifies a willingness-to-pay or benefit schedule that is relatable for the assessment of various public policies. As such, aircraft noise in relation to hedonic pricing models observes several analytical concerns. Majorly, the first consideration takes into account the specification of the model used to detach noise effects from numerous conceivable influences on the value of properties. The second analytical issue is the transferability of the benefits of noise abatement across countries, regions and urban markets. As such, the use of meta-analysis techniques indicates that aircraft noises bring about the permeation of not only the hedonic pricing within the housing industry but also negative side effects among the residents living adjacent to major airport hubs.
Solutions
The noises that aircrafts produce continue to pose a significant barrier to the continual expansion of airport operations. While growth permeates on the reduction of aircraft emissions within the last decade alone, there is the need for more augmentations on improvements due to the rapid growth of airport operations. As such, the only solution remains the resultant reduction in the impact of aircraft noises, which can be done through various ways. Among them includes the limitation of aircraft aerodynamic and power plant noises through the redesign of flight procedures and flight guidance technology (Clarke, 2000). Principally, typical flight procedures include aircraft departure, arrival, and approach. As such, in reference to the redesign of flight processes, noise abatement procedures can involve the use of preferential routings that avoid the flight over populated areas and the use of enhanced vertical flight path profiles that involves the adjustment of thrust settings, flight speeds and configurations in the flap and slat procedures. However, current procedures of noise abatement present, in relation to the noise impact procedure, far more optimal methodologies. In special cases, optimization of in-flight procedures becomes impossible due to limitations in navigation complexities and methods currently employed in certain terminal airspaces. On the other hand, the application of multi-objective optimization strategies has resulted in more ostentatious methodologies that have minimized noise annoyance levels as exhibited at the Girona Airport, Catalonia, Spain (Prats, Puig & Quevedo, 2011).
The multi-objective optimization methodology employed for the abatement of aircraft noises employs the use of objective functions in measuring the deviation in annoyance at each point of noise measurement from the ideal values that correlate to prime annoyance. Therefore, if the absolute annoyance levels were used as a criterion for optimization, the inherent solution would result in excessive locational sensitivity as per proximity to the airport; a site-specific criterion in the optimization of noise abatement trajectories (Visser, 2005). For example, if the ideal measured annoyance value, say at location A is 0.5 and at location B is 0, a subjective judgment transpires indicating the unfairness of equally minimizing A and B since the process of optimization gives more priority to the minimization of noise annoyance at location A rather than location B. Thus, this makes the optimization methodology to reflect a compound strategy that incorporates several multi-criteria techniques in overall optimization. Such techniques incorporated to the overall optimization methodology include goal optimization, the hierarchical optimization of operational costs, the lexicographic-egalitarian optimization, and the overall optimization methodology (Prats, Puig & Quevdo, 2011). This overall methodology places, in summary, proposed optimization strategies for any given hour within airports. The procedure follows a precise measurement basis that first analyzes residential and industrial zones, followed by hospitals and schools, and finally the individual calculation of objective optimizations in an effort to compute ideal values at residential and industrial areas.
Another strategy in the mitigation of aircraft noise is the implementation of the continuous descent arrivals and take offs. The continuous descent arrival (CDA) refers to the technique of operating a plane, whereby, an arrival aircraft descends from an optimal position using minimized thrusts and the avoidance of level flight to the extent that is safe as regulated by the safe operations stipulations and the aircraft compliance in relation to published procedures and instructions. Therefore, in actualizing such descents, the major objective of CDA is to ensure a reduction in fuel burn, aircraft noise, and emissions. This commensurately results in an interception of the approach path of glide at appropriate altitudes to effect reasonable distances to touchdown. In addition, the combination of CDA techniques with the prerogative to keep the aircraft as high as possible results in effectiveness at significantly reducing the impact from the noise on the ground. Besides, measures in CDA ensures the aircraft remains in a Low-Power/Low-Drag state, significantly minimizing the resultant noise disturbance of the plane. In comparison to non-CDA approach profiles, aircrafts that exhibit CDA profiles significantly reduce the production of harmful noise levels. In an orthodox non-CDA approach, the aircraft descends stepwise, with significant portions of level flights between the descents. As such, while non-CDA approaches appear more to the ground, CDA ones are much higher and use fewer engine thrusts, resulting in a significant reduction of noises.
Noise abatement in aircrafts is also achievable through the implementation of reduced thrust, particularly, during takeoff (Girvin, 2005). Through the reduction of thrust, the impediment of intense noise propagation transpires subsequently debilitating its effects on property value dynamics and individuals living around airports. Reduced thrust takeoffs are accomplished using less thrust than the capabilities of the engines under preexisting temperature conditions and pressure altitudes. According to the Aerodrome Operating Minima (AOM), which refers to the criteria used by pilots to judge landings and takeoffs from various runways, limitations specify various criteria according to the length, obstacles and altitudes factored against aircraft weight that regulates takeoff requirements. Such factors usually translate to a determination of thrust, of which in a significant amount of cases, the thrust is less than the production capacity of engines. While the primary advantage of employing the use of minimized thrust is the savings of cost through increased engine life and overall overhaul costs, secondary advantages in increased fuel savings and a mitigation of significant jet noises is a plus for strategies in reducing hedonic property value and harmful environmental noise pollution. In consideration of jet engine limitations, the application of reduced thrust solves pertinent aircraft issues as well as the resultant consequences emanating from noise pollution. Therefore, as an abatement strategy, it is highly applicable and recommendable.
Analogous to Continuous Descent Arrivals, the implementation of Continuous Climb Operations (CCO) also results in significant environmental benefits in terms of emissions and noise reductions (Erkelens, 2000). In a departing aircraft, the optimal vertical profile represents a continuous climbing path, which represents the optimal fuel conserving climb rate. Thus, the fuel used in ascending to the most fuel-efficient level is normally a germane part of the overall fuel consumed for the flight. This makes the CCO permit the aircraft in reaching initial cruise flights at levels that are optimum to the airspeed and settings that represent optimal engine thrusts. Through the application of these optimal engine thrust settings, the total fuel burn and emissions for the whole flight are significantly reduced. Moreover, before the plane taking off, the application of CCO methodologies results in a reduction of controller workload and flight crew; consequently, leading to a situation that requires less Air Traffic Control intervention. All these reductions subsequently mitigate the overall operating power required by the aircraft, ultimately, minimizing environmental hazards emanating from noise and emissions pollution. As such, through the mitigation of these environmental impacts, hedonic property pricing, especially around airport facilities, becomes minimized effectively translating to fewer complexities in property sales
Another method of noise abatement is the implementation of Noise Abatement Departure Procedures (NADP) during departure (Girvin, 2009). Such mitigation procedures are crucial in minimizing the noises generated during departure; subsequently, curtailing the resultant effects of aircraft noise on property value and the health of individuals. During departure, the primary aim of the flight crew is to accelerate the aircraft to a speed that renders it conducive for takeoff. At 800 feet or above in altitude, as defined by various flight bodies, the engine power may be reduced to preserve an adequate service life for the engine and to significantly reduce the environmental impact emanating from the noise levels and engine emissions while at full power. This intricate balance in the amount of energy needed in gaining speed and altitude, and at what altitude power reduction and acceleration require initiation is what has the consideration of being the noise abatement departure procedure(s) in aviation. Such procedures are subsequently incorporated into the standard operating procedures of the airline company in question resulting in the realization of reductions in noise levels. Moreover, NADP methodologies are highly regulated to ensure the non-proliferation of its intricate steps, which may lead to confusion and an impact on safety levels. As such within the regulations in the European Union, there is the placement of special guidelines that recommend not more than two procedures for all aircraft types. Such procedures are pertinent in ensuring proper compliance to noise abatement strategies leading airports and their vicinities to be safe from noise pollution.
To abate noise production also, upon arrival, aircrafts can implement certain applicable procedures. Such procedures include approaches such as the two-segment and slightly steeper approaches, the use of displaced landing thresholds, and the use of a reduced landing flap (Civil Aviation Authority, 2014). In the case of a reduced landing flap, most aircrafts have the certification of having two pertinent landing flap settings. The first setting represents a full landing setting that places the flaps in question at a maximum angle, subsequently, producing maximum drag. In a reduced landing flap setting, a significant reduction of the angle of the landing flap commensurately reduces the force of drag, thereby, demanding a reduced amount of engine power that results in a reduction of noise emissions. While reduced landing flaps have their pros in noise reduction, its cons are that it leads to an increased wear in the braking system and an increased occupancy of the runway. On the other hand, its fuel burn reduction and engine emissions are environmental-friendly making the use of reduced landing flaps highly common in various areas within the air travel industry. In the method of displaced landing thresholds, the achievement of noise reduction takes place through the supplanting of the thresholds in airport runways from the extremity of the end of runway surfaces to a location that is further down the runway. Such displacements allow aircrafts to fly higher above communities, thereby, increasing the distance of noise propagation, leading to the stabilization of its effects.
In the case of the implementation of a slightly steeper approach in noise abatement, its use is presently undergoing tests; moreover, the extrapolation of conclusive evidence has not yet taken place (Civil Aviation Authority, 2014). The international standard Instrument Landing System (ILS) stipulates a typical glide path of an angle of 3 degrees and not more; nonetheless, augmenting the glide path of an aircraft reduces the production of annoying noise in two pertinent ways. First, this increase in angling increases the aircraft height above ground, which increases the distance over which the traveling of sound takes place prior to reaching the population of communities below. Secondly, greater angling proliferates the rate of descent, subsequently reducing the engine power needed, thus abating the noise emitted. Presently, in the UK, various airports are employing the use of angles greater than 3 degrees for their glide paths to account for various obstacles and in the process reduce noise pollutions. While this strategy is implementable, it is only efficient in instances whereby there are no low visibilities and much preferably, during the daytime. On the other hand, the two-segment approach caters for the fail in low-visibility weather using slightly steeper approach angles and the subsequent revert to the standard 3-degree angle. While this provides potential noise reductions, it is in essence not as effective as the slightly steeper approach. Moreover, issues with this concept to do with technical feasibility, environmental impacts, benefits in airport capacity and its scalability are still in question.
Other noise reduction strategies apply mainly on the airport ground and are necessary for ensuring the abatement of this type of pollution. One of the most common ways is the use of noise insulation in residential properties and buildings that require keenness on noise sensitivity such as hospitals and schools. While the transmission of noises from the outside inside occurs through a complex process that is highly dependent on various factors such as the walls and the windows, together with their construction materials, the greatest transmission occurs through the windows which may rake in close to 19 dB of redundant noise levels (Civil Aviation Authority, 2014). Other on-the-ground mitigation strategies include the consideration of eligibility criteria and the implementation of proper funding for the eligibility and support of noise insulation.
Conclusion
For the environment to realize a noise pollution future and for the control of hedonic property values within real estate markets relative to airport proximity, the implementation of the aforementioned strategies in minimizing aircraft noises is highly imperative. Moreover, noise abatement measures provide numerous cost-benefit advantages such as harmonizing the social structure, which commensurately brings about economic stability (Nijland, Van Kempen, Van Wee & Jabben, 2003). Nonetheless, various numerous constraints within the system result in a prevention and hindrance of noise abatement procedures particularly in relation to continuous descent arrivals. Such hindrances include the lack of guidance that is in harmony; the high airspace capacity requirements; the airport/ground equipment, which requires space and proper funding; aircraft equipage; the lack of proper skills and training; economic limitations; the lack of or poor quality of information; among others. These factors inevitably result in a reduction of noise abatement operational procedures within the vicinity of airports, leading to resultant effects on individuals and property prices. While the environmental benefits of abatement procedures are straightforward and easy to envisage, alterations in hedonic property values are often complex
Hedonic property values indicate that present-day results remain consistent with earlier contributions, which concluded that the noise discount is at a maximum of 0.6% per dB in the United States (Nelson, 2004). Therefore, a particular property located at a noise level of 55 dB would sell for close to 10-12 percent less if it were at a decibel level of say 72, with respect to proper constancy in variables. Such extrapolations remain stout even in the face of analytical methods such as the use of Geographical Information Systems, contemporary hedonic research, as well as other spatial autocorrelation techniques in pricing houses. Overall, through the proper and consistent implementation of the aforementioned aircraft control solutions, underlying problems in both the health of individuals and the existence, persistence, and fluctuations in hedonic property price value will be solved.
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