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The psycho-social consequences of aircraft noise
Applied Ergonomics 1973, 4.1, 44-45
The psycho-social consequences of aircraft noise H.C.W. Stockbridge and Mary Lee Principal Psychologistand Scientific Officer of the Scientific Adviser's Division, Civil Aviation Authority. The paper describes and compares various methods of investigating the social disamentity caused by aircraft noise. These methods include social surveys, the analysis of complaints, and direct observation. Each has practical, political and statistical advantages and disadvantages. The effects of aircraft noise are also discussed and the conclusion is drawn that if social pressure continues to be applied, the technologists can and will quieten aircraft engines. As the title suggests, we are confronted with the problem of evaluating any social disamenity caused by aircraft noise. We have to obtain information from householders near an airport and equate this information with the known patterns of exposure to aircraft noise in that area. It may be almost impossible objectively to evaluate the adverse effects caused by aircraft noise since identifiable effects, such as deafness, seldom occur. Obtaining information on the effects of aircraft noise may be approached in two main ways: passively waiting for complaints against aircraft noise, or actively making a social survey of opinions of a sample of the population round the airport. Both these methods have been used for Heathrow airport. An alternative method is to take direct measurements, where we attempt to record the extent to which a bodily activity or function is interrupted by aircraft noise. This type of approach has not been widely used except in the area of sleep disturbance.
Social surveys First, we would like to consider the use of social surveys in defining the aircraft noise problem. In the UK, two main surveys were carried out around Heathrow airport in 1961 and 1967. In the first survey (Anon, 1968), a seven point scale of annoyance was derived, with zero signifying no annoyance. The physical variables measured included the mean peak noise level and the number of aircraft heard per day. The analysis was carried out using grouped data and the main aim was to equate exposure to annoyance. The main result of this survey came from graphical plots of the annoyance scores against the two physical variables, noise and number, which gave an index, the noise and number index (NNI). The equation for calculating the NNI is given below: N N I = L + 15 Log l o N - 8 0 Using this formula, a value of 50-60 NNI was considered to represent unreasonably high exposure. Above this level, people thought that aircraft noise was roughly the same by day and by night. A comparison of exposures by day and night led to the proposal that the NNI values corresponding to night should be 15-20 NNI lower than the day NNI. For example, the critical day limit of 50-60 NNI is by night 30-45 NNI.
44
Applied Ergonomics March 1973
Second survey The 1967 survey (Anon, 1971) covered a larger area than the first survey, but used the same scale of annoyance. The main aims were to find out whether the results of the 1961 survey were still valid and what changes, if any, had occurred over the six year period. The main form of analysis used was regression analysis using a computer. An updated form of the NN1 formula was derived as shown below: NNI=L+4Log
10 N - 8 0
This formula should not be directly compared with the 1961 formula because of slight differences in the methods of obtaining the physical data, particularly the number of aircraft heard per day. The 1967 survey results did not lead to any change from the original 1961 NNI formula, since the evidence for the new formula was not considered powerful enough to initiate a change - or rather it was not considered that the 1967 survey results negated the results of the previous survey, if a formula embodying only L and N (with N counted only in the 12 daytime hours) were retained. It was thought that background noise, nighttime factors and perhaps other effects ought to be considered fully before the Index was revised. The 1967 survey failed to provide any convincing results on the annoyance felt by night. One form of analysis does suggest that there is a range of differences of between 12 and 30 NNI between day and night - the difference increasing with increasing levels of exposure. These results agree fairly well with the 1961 results excepting that the range is larger. In both the surveys, correlations between annoyance and exposure to aircraft noise lie in the range 0.4 to 0.45. This suggests either that these variables do not truly represent the parameters which they are attempting to define, or that the low correlations are characteristic of the variability of human response to stimuli. In both surveys psycho-social variables such as 'fear' and 'general attitude to noise' are closely related to annoyance. The design of future surveys should therefore be based on using alternative and hopefully more valid measures of aircraft noise and of the reactions of the survey sample to this noise exposure. A more realistic measure of the noise level should take into account the background noise level
in the area under consideration. Precise measurements would be impossible due to the continual fluctuations of background noise levels. Instead of estimating the average number of flights passing over an area per day, some measure of the time intervals between flights could be made. This will differentiate between areas exposed to large amounts of traffic at only specific times of the day, and areas exposed to aircraft throughout the day. As an alternative to the annoyance scale used in the past, new scales measuring interruption of activities and annoyance, separately, might improve the measurement of human response to noise. A measure of interruption of activities should correlate fairly highly with exposure since it is a fairly objective measurement. However, the annoyance which the noise causes is a completely subjective reaction and therefore we would not expect high correlations between this variable and exposure. We must also consider whether a scale of annoyance, which is subject to so much scatter between individuals, is a proper or practical measure of'environmental disamenity. Interruption of activities by noise would best be measured by direct observation rather than by survey methods. This could be carried out in such places as schools and hospitals and it might be possible to derive a limit of exposure above which people could not be expected to work, sleep or participate in other activities.
The analysis of complaints A further method of defining the effects of aircraft noise is the analysis of complaints. Each year, complaints received from the Heathrow area total about 3000 over the Summer months (April - September). Analysis shows that the number of complaints is closely related to the number of movements made at the airport. Thus complaints are far more in the summer when the number of movements is highest. Here we seem to have reached similar conclusions as Burrows (1972) but by different routes, namely that irritation is closely related to number of aircraft movements made. Unpublished research suggests that complaints are 'triggered' by situations considered to be new or unusual, or by any form of publicity. Thus changes in routes, the introduction of a new aircraft type, or any event likely to draw the public's attention to aircraft noise, will cause a sudden increase in the number of complaints received. This suggests that maintaining the status quo and avoiding any form of publicity may lead to a reduction in the number of complaints, or at least keep them constant.
at one moment in time. Thus social surveys have fundamental statistical drawbacks.
The effects of aircraft noise Aircraft noise is often considered together with such problems as air, water and other forms of pollution. In comparison with these other forms of pollution it may be thought of as the least important, since it has as yet no identifiably permanent effect on the population, and the pollution is very localized. An aircraft passes overhead, the noise interrupts a school lesson, or a phone conversation, but within a few seconds all is quiet again. Thus the effect appears to be only transitory. If we consider further, however, the effect may not be so transitory in nature. If the frequency of interruptions reaches a certain level it may have a lasting effect on the ability of a child at school or the efficiency of an adult at work. It may also cause frustration, shortened temper and inability to concentrate. The primary effect of aircraft noise is the disturbance of activities such as conversation (this includes teaching and phone conversations), work and concentration, listening to the radio, and sleep. The level of acceptability of noise will depend on the individual concerned. Thus legislation cannot take care of all tastes. Survey results suggest that about 20% of the population are 'imperturbable' and are only slighly annoyed however high the exposure. At the other end of the scale, about 10% of people, in the quietest areas surveyed, are seriously annoyed. There is certainly good reason to be concerned about people living very near the airport, but the problem may be self-solving. Although no statistical evidence is available it it plausable that those who are highly disturbed will move away from the area, while those taking their places will be aware of the problem. Thus the area may gradually be filled by the 'imperturbables'.
Conclusion The only finally satisfactory and acceptable answer is the quietening of aircraft. This can be done, we are told, by the plane-makers, but at a cost in time and money. It is, however, clear that dramatic improvements are already being made, and if social pressure continues, the technological forecast indicates that aircraft noise can be largely overcome in about two decades.
Acknowledgment
The last observation reduces the value of complaints data in evaluating the effects of aircraft noise, but it also has implications for social surveys.
Based on a paper presented by the authors at the 20th International Congress of Aviation and Space Medicine (1972) and published with the agreement of the organisers of this conference.
A comparison of the survey and complaint methods
References
Both the survey method and the analysis of complaints have their strengths and their weaknesses. Social survey methods put ideas into people's heads which may or may not have been there before. Complaints tend to come from the articulate, affluent house-holders in the community and therefore do not represent a random sample of the population. Finally, complaints can be collected over long periods of time but market research gives a cross-section of opinion
Anon 1968 (reprint) "Noise - Final Report", Committee on the Problem of Noise, HMSO, Cmnd 2056. Anon 1971 Second Survey of Aircraft Noise Annoyance around London (Heathrow) Airport, HMSO, SS 394.
Burrows, A.A. 1972 Aircraft noise and the community: Some recent survey findings. AerospaceMedicine, 43, 27-38.
Applied Ergonomics March 1973
45
The psycho-social consequences of aircraft noise H.C.W. Stockbridge and Mary Lee Principal Psychologistand Scientific Officer of the Scientific Adviser's Division, Civil Aviation Authority. The paper describes and compares various methods of investigating the social disamentity caused by aircraft noise. These methods include social surveys, the analysis of complaints, and direct observation. Each has practical, political and statistical advantages and disadvantages. The effects of aircraft noise are also discussed and the conclusion is drawn that if social pressure continues to be applied, the technologists can and will quieten aircraft engines. As the title suggests, we are confronted with the problem of evaluating any social disamenity caused by aircraft noise. We have to obtain information from householders near an airport and equate this information with the known patterns of exposure to aircraft noise in that area. It may be almost impossible objectively to evaluate the adverse effects caused by aircraft noise since identifiable effects, such as deafness, seldom occur. Obtaining information on the effects of aircraft noise may be approached in two main ways: passively waiting for complaints against aircraft noise, or actively making a social survey of opinions of a sample of the population round the airport. Both these methods have been used for Heathrow airport. An alternative method is to take direct measurements, where we attempt to record the extent to which a bodily activity or function is interrupted by aircraft noise. This type of approach has not been widely used except in the area of sleep disturbance.
Social surveys First, we would like to consider the use of social surveys in defining the aircraft noise problem. In the UK, two main surveys were carried out around Heathrow airport in 1961 and 1967. In the first survey (Anon, 1968), a seven point scale of annoyance was derived, with zero signifying no annoyance. The physical variables measured included the mean peak noise level and the number of aircraft heard per day. The analysis was carried out using grouped data and the main aim was to equate exposure to annoyance. The main result of this survey came from graphical plots of the annoyance scores against the two physical variables, noise and number, which gave an index, the noise and number index (NNI). The equation for calculating the NNI is given below: N N I = L + 15 Log l o N - 8 0 Using this formula, a value of 50-60 NNI was considered to represent unreasonably high exposure. Above this level, people thought that aircraft noise was roughly the same by day and by night. A comparison of exposures by day and night led to the proposal that the NNI values corresponding to night should be 15-20 NNI lower than the day NNI. For example, the critical day limit of 50-60 NNI is by night 30-45 NNI.
44
Applied Ergonomics March 1973
Second survey The 1967 survey (Anon, 1971) covered a larger area than the first survey, but used the same scale of annoyance. The main aims were to find out whether the results of the 1961 survey were still valid and what changes, if any, had occurred over the six year period. The main form of analysis used was regression analysis using a computer. An updated form of the NN1 formula was derived as shown below: NNI=L+4Log
10 N - 8 0
This formula should not be directly compared with the 1961 formula because of slight differences in the methods of obtaining the physical data, particularly the number of aircraft heard per day. The 1967 survey results did not lead to any change from the original 1961 NNI formula, since the evidence for the new formula was not considered powerful enough to initiate a change - or rather it was not considered that the 1967 survey results negated the results of the previous survey, if a formula embodying only L and N (with N counted only in the 12 daytime hours) were retained. It was thought that background noise, nighttime factors and perhaps other effects ought to be considered fully before the Index was revised. The 1967 survey failed to provide any convincing results on the annoyance felt by night. One form of analysis does suggest that there is a range of differences of between 12 and 30 NNI between day and night - the difference increasing with increasing levels of exposure. These results agree fairly well with the 1961 results excepting that the range is larger. In both the surveys, correlations between annoyance and exposure to aircraft noise lie in the range 0.4 to 0.45. This suggests either that these variables do not truly represent the parameters which they are attempting to define, or that the low correlations are characteristic of the variability of human response to stimuli. In both surveys psycho-social variables such as 'fear' and 'general attitude to noise' are closely related to annoyance. The design of future surveys should therefore be based on using alternative and hopefully more valid measures of aircraft noise and of the reactions of the survey sample to this noise exposure. A more realistic measure of the noise level should take into account the background noise level
in the area under consideration. Precise measurements would be impossible due to the continual fluctuations of background noise levels. Instead of estimating the average number of flights passing over an area per day, some measure of the time intervals between flights could be made. This will differentiate between areas exposed to large amounts of traffic at only specific times of the day, and areas exposed to aircraft throughout the day. As an alternative to the annoyance scale used in the past, new scales measuring interruption of activities and annoyance, separately, might improve the measurement of human response to noise. A measure of interruption of activities should correlate fairly highly with exposure since it is a fairly objective measurement. However, the annoyance which the noise causes is a completely subjective reaction and therefore we would not expect high correlations between this variable and exposure. We must also consider whether a scale of annoyance, which is subject to so much scatter between individuals, is a proper or practical measure of'environmental disamenity. Interruption of activities by noise would best be measured by direct observation rather than by survey methods. This could be carried out in such places as schools and hospitals and it might be possible to derive a limit of exposure above which people could not be expected to work, sleep or participate in other activities.
The analysis of complaints A further method of defining the effects of aircraft noise is the analysis of complaints. Each year, complaints received from the Heathrow area total about 3000 over the Summer months (April - September). Analysis shows that the number of complaints is closely related to the number of movements made at the airport. Thus complaints are far more in the summer when the number of movements is highest. Here we seem to have reached similar conclusions as Burrows (1972) but by different routes, namely that irritation is closely related to number of aircraft movements made. Unpublished research suggests that complaints are 'triggered' by situations considered to be new or unusual, or by any form of publicity. Thus changes in routes, the introduction of a new aircraft type, or any event likely to draw the public's attention to aircraft noise, will cause a sudden increase in the number of complaints received. This suggests that maintaining the status quo and avoiding any form of publicity may lead to a reduction in the number of complaints, or at least keep them constant.
at one moment in time. Thus social surveys have fundamental statistical drawbacks.
The effects of aircraft noise Aircraft noise is often considered together with such problems as air, water and other forms of pollution. In comparison with these other forms of pollution it may be thought of as the least important, since it has as yet no identifiably permanent effect on the population, and the pollution is very localized. An aircraft passes overhead, the noise interrupts a school lesson, or a phone conversation, but within a few seconds all is quiet again. Thus the effect appears to be only transitory. If we consider further, however, the effect may not be so transitory in nature. If the frequency of interruptions reaches a certain level it may have a lasting effect on the ability of a child at school or the efficiency of an adult at work. It may also cause frustration, shortened temper and inability to concentrate. The primary effect of aircraft noise is the disturbance of activities such as conversation (this includes teaching and phone conversations), work and concentration, listening to the radio, and sleep. The level of acceptability of noise will depend on the individual concerned. Thus legislation cannot take care of all tastes. Survey results suggest that about 20% of the population are 'imperturbable' and are only slighly annoyed however high the exposure. At the other end of the scale, about 10% of people, in the quietest areas surveyed, are seriously annoyed. There is certainly good reason to be concerned about people living very near the airport, but the problem may be self-solving. Although no statistical evidence is available it it plausable that those who are highly disturbed will move away from the area, while those taking their places will be aware of the problem. Thus the area may gradually be filled by the 'imperturbables'.
Conclusion The only finally satisfactory and acceptable answer is the quietening of aircraft. This can be done, we are told, by the plane-makers, but at a cost in time and money. It is, however, clear that dramatic improvements are already being made, and if social pressure continues, the technological forecast indicates that aircraft noise can be largely overcome in about two decades.
Acknowledgment
The last observation reduces the value of complaints data in evaluating the effects of aircraft noise, but it also has implications for social surveys.
Based on a paper presented by the authors at the 20th International Congress of Aviation and Space Medicine (1972) and published with the agreement of the organisers of this conference.
A comparison of the survey and complaint methods
References
Both the survey method and the analysis of complaints have their strengths and their weaknesses. Social survey methods put ideas into people's heads which may or may not have been there before. Complaints tend to come from the articulate, affluent house-holders in the community and therefore do not represent a random sample of the population. Finally, complaints can be collected over long periods of time but market research gives a cross-section of opinion
Anon 1968 (reprint) "Noise - Final Report", Committee on the Problem of Noise, HMSO, Cmnd 2056. Anon 1971 Second Survey of Aircraft Noise Annoyance around London (Heathrow) Airport, HMSO, SS 394.
Burrows, A.A. 1972 Aircraft noise and the community: Some recent survey findings. AerospaceMedicine, 43, 27-38.
Applied Ergonomics March 1973
45