Despite a vast global airspace, aircrafts have historically tended to follow a predetermined pattern that is somewhat akin to roads for automobiles [1
]. For a long time, flights were primarily guided by radar and radio [2
]. As with other areas of transportation, however, automated flight systems are gradually being rolled out. NextGen is one these automated systems that uses GPS, data from other flights, and atmospheric conditions to optimize flight patterns [1
]. NextGen has also the potential to reduce pollution, flight time, costs, and accidents due to human error [4
]. Its use, however, has resulted in changes in flight patterns that might go over densely populated residential areas, which pose public health threats by potentially exposing people on ground to a loud and continuous noise [1
]. One example of the impact of NextGen can be found in New York City, where it effectively led to the year-round use of the otherwise restricted “TNNIS Climb” at LaGuardia Airport (LGA) since its implementation.
The TNNIS Climb had been historically used only during the U.S. Open, a large tennis tournament held within a park in Queens, NY, USA, that is adjacent to LGA airport. Historically, flights departing from LGA flew over the tennis stadium in Flushing Meadows and over other sparsely populated areas, such as the East River. However, because the roar of jet engines was loud enough to disrupt the matches, flights were instead diverted over densely populated residential neighborhoods of Queens (mainly Community Boards 7 and 11), NY, USA, during tennis matches. This flight, which uses runway 13 at LGA, is coded TNNIS and is known as the TNNIS Climb [5
In the era of NextGen, use of runway 13 at LGA has become a common route of departure, and TNNIS Climb has become year-round [6
]. The trajectories of the TNNIS and the Whitestone Climbs which are the two major departure routes of the runway 13 at LGA are provided elsewhere [9
]. The year-round use of TNNIS has produced large increases in aircraft noise for residential areas of Community Boards 7 and 11 of Queens, NY, USA. These neighborhoods were previously quiet. High levels of exposure to aircraft noise has been linked to development of serious physical and mental health conditions such as cardiovascular disease (CVD) and anxiety [11
]. In this paper, we quantified the potential health and economic consequences of the year-round use of TNNIS at LGA in Queens, NY, USA, and asked whether its benefits would outweigh the noise-associated health risks experienced by people in what were once quiet communities.
Flight pattern optimization can, in theory, produce profound societal benefits. These include reduced atmospheric pollution, gains in productivity from reduced flight time, and increases in the timely delivery of products and services. NextGen is a recently implemented automated system at airports that optimizes flight patterns in the sky and improves flight efficiency. Airports are one of the primary points of commercial activities, and optimizing flight patterns can have positive spillover effects on the economy. However, it can also have negative impacts on health, resulting in unintentional harm and unforeseen costs. This, in turn, also produces negative spillover effects.
In this study, we examined the potential health and economic impacts of a change in one flight route, TNNIS Climb, in NY. This route was originally used only during U.S. Open tennis tournament, but has become year-round since NextGen was implemented in 2012. We found that the ICER of the limited use of TNNIS (old status quo) would be $
10,006/QALY gained compared to its year-round use (current status quo). This suggests that, based on a subset of health and economic endpoints that was modelled in this study, it is likely that limiting the use of TNNIS would be cost-effective relative to its year-round use. Doing so would prevent much more disease at a much lower cost than commonly used clinical health prevention modalities, such as colon cancer screening or mammography [54
]. Because we found that limiting the use of TNNIS would result in an ICER below the recommended WTP threshold values for cost-effectiveness [56
], we did not attempt to add further cost savings from productivity or other spillover effects for people on ground, such as future lost tax revenue, social service consumption, and crime costs associated with lower educational attainment [57
]. Future studies that focus on less densely populated sound corridors with smaller airports may show fewer health costs, and may therefore need to account for some of these other important health and economic endpoints.
This provides a segue into the limitations of our study. First, our study focuses on the increased use of one flight route that might have been influenced by the implementation of NextGen in one location. It does not speak about the broader trade-offs produced by NextGen in other locations as we deem critically important to explore impacts locally on a case-by-case basis. Therefore, our model is available on demand to the research community so that it can be modified for nearly any local context. Second, it is challenging to estimate the exact noise exposure associated with overflights on ground. We used sound corridor data from the Port Authority and real-time sound data. While the real-time observations of sound monitors show sounds in excess of 90 dB when an aircraft overflies the residential areas of Community Boards 7 and 11 of Queens, NY, we did not have continuous sound monitor data. We assumed that the noise exposure would have dropped to levels around or below the baseline 50 dB for people living within the 60 dB DNL noise contour had not TNNIS been used year-round. Also, the real-time system we used shows the size of the aircraft, but generally does not show all aircrafts in the area. Third, we only modeled CVD and anxiety as health consequences of noise even though there are a wider array of potential health and economic endpoints of aircraft noise. Our model is similar to a previously published cost-effectiveness model exploring the health impacts of aircraft noise [58
], and we were not able to incorporate other studies of noise and health [26
]. This is because the use of other studies would require that we make broader assumptions surrounding the dose-response relationship between noise and other types of health endpoints. As such, our results solely rely on the applicability and generalizability of the previous findings by Hansell et al. [14
], in association of noise and CVD, and Hardoy et al. [15
], in association of noise and anxiety, to the setting of our study. Fourth, Hardoy et al. provided an overall estimation for risk of anxiety due to aircraft noise with no specification for noise levels [15
]. In this study, we assumed that the relative risk of developing anxiety as reported by Hardoy et al. would be applicable to our dichotomized noise exposure levels (>60 vs. <50 dB DNL), and that we assumed noise below 50 dB DNL would not be harmful for health. This has some support from literature, as studies have shown 55 dB DNL is the threshold at which health problems would arise [11
]. To account for such uncertainty, in our sensitivity analyses, we used a wide range of error in our measure of association of anxiety and the noise categories of our model. Finally, efficiencies are associated with fewer emissions and air pollution. However, there is little information on how varying flight patterns over urban areas impacts particulate concentration on ground, and this potentially important benefit of the year-round use of TNNIS was not included.
Our study explores the cost-effectiveness of one air route in one city that insists over an unusually densely populated area. Though our estimates of health impacts were informed from published studies, it is very difficult to fully account for the broader economic impacts of the year-round use of TNNIS. Our study should by no means be taken as a blanket assessment of changes to flight patterns that might reduce airline fuel consumption, increase productivity, and reduce global warming. However, they point to the strong need for careful study of public health impacts of such changes before they are implemented. NextGen holds great potential for improving our lives. However, it also appears to produce an increase in disability and death, at least in New York City. Most people have some experience with unpleasant noise in their environment (be it sirens, honking, or aircraft), yet remarkably little is known about it or is done about it. We hope that models such as ours can be used to better understand the trade-offs that new technologies bring.