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Community response to noise from short-term military aircraft exercise
Journal of Sound and Vibration (1995) 182(2), 221–228
COMMUNITY RESPONSE TO NOISE FROM SHORT-TERM MILITARY AIRCRAFT EXERCISE T. G, K. H. L I. L. N. G SINTEF DELAB, N-7034 Trondheim, Norway (Received 4 November 1993, and in final form 14 February 1994) A study of community reactions to noise in the vicinity of a Norwegian airport has been conducted in connection with two large military exercises. An extensive questionnaire was presented to a random sample of residents before, during and after each exercise. More than 3400 interviews were completed. The group of respondents also contained a panel of about 200 people who were given identical questions in each survey series. This paper presents the results with an emphasis on the data from this panel. The results indicate that the general reaction to aircraft noise is not altered by short periods with increased noise exposure.
1. BACKGROUND
A number of Norwegian airports serve both civil and military traffic, and occasionally these airports are used for military aircraft exercise purposes. The exercises include operations by fighters, helicopters and transport aircraft, and during these periods the total number of daily operations increases considerably with a corresponding shift in the noise exposure. The environmental impact on the community in the vicinity of these airports thus changes dramatically, and there is a potential chance that the community reaction to aircraft noise changes in a negative direction. An extensive study of community reactions to aircraft noise has been conducted in the vicinity of a Norwegian airport that serves both civil and military traffic. Two large military exercises took place in the study period. During these exercises the number of aircraft operations increased significantly, and the total noise exposure increased by about 6 dB for a period of 2–3 weeks. Social surveys were conducted before, during and after these exercises and more than 3400 interviews were completed. The respondents were mainly naı¨ ve residents, but a panel of about 200 persons was also established. These 200 persons were interviewed throughout the study period. Their responses were recorded on an individual basis, so that the data can be analyzed with respect to changes in the response for each single panel member.
2. STUDY DESIGN
The exercises took place in March and September 1992. Telephone interviews were conducted before, during and after the first exercise, and before and after the second exercise. Noise measurements and radar tracking of the air traffic were carried out in order to obtain a precise description of the total noise exposure. About 500 naı¨ ve respondents participated in each series of interviews, together with a panel of about 200. 221 0022–460X/95/170221 + 08 $08.00/0
7 1995 Academic Press Limited
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A list of all private telephone subscribers in the area was supplied by the local telephone company. The subscribers were sorted into different groups according to their normal noise exposure, each group covering a range of 5 dB(A) corresponding to established ‘‘noise zones’’. Within each group a random selection of telephone numbers to call during each series was made. The number of subscribers in each group was sufficiently large to obtain the desired sample size after adjusting for refusals and other types of non-response. In each subscriber household the interviewer asked to interview whichever resident would be the next to have a birthday. Respondents were required to be more than 15 years of age. Repeated calls (four or five times) were made if the selected individual was not initially available. At the end of the initial interview, the respondent was asked if he or she would be willing to participate in future study series; in other words, to be part of a survey panel. Those who volunteered were identified by name, so that the right individual could be located for the next series. A panel of 200 respondents was randomly selected from this group. The questionnaire was presented as a general survey of neighborhood condition, and also contained a number of demographic and other non-aircraft related issues. The results from the different survey periods were analyzed with respect to any shift in reaction due to changes in the aircraft operations. The main questions were as follows: Can the dose–response relationship established for the normal situation also be applied to an exercise period? Is there an ‘‘over-reaction’’ caused by large changes in the noise exposure? 3. NOISE SITUATION
The regular air traffic at this particular airport consists of about 140 civil and 70 military movements per day (take-offs or landings). During the exercise periods the number of military movements increased to about 130 per day and at the same time the civil traffic was reduced to 110. The regular civil traffic consists of 16% jet, 60% turboprop, 22% single and twin engine GA propeller traffic, and 2% helicopters. The military traffic consists of 69% fighter aircraft, 18% transporter aircraft and 13% helicopters. The noise levels in the area have been recorded and compared with results from the INM Aircraft Noise Calculation Program, using the actual air traffic as input. The INM Program, initially developed by the US Federal Aviation Administration, is used to calculate noise zones for land-use purposes around Norwegian airports. The difference between the actual measurements and the calculated noise levels were small, typically 1–2 dB(A). Calculated noise levels have therefore been used for the remainder of this paper. Norway has adopted a special aircraft noise index called EFN, the Equivalent Aircraft Noise Level. This is an energy equivalent time weighted noise index. Noise events during the night period are penalized by a factor of ten (equal to 10 dB), while noise events during the morning and evening transition periods are penalized with graduated weight. Noise events on Sundays are penalized by a factor of three (5 dB). EFN resembles the Community Noise Equivalent Level, CNEL. The only difference is that EFN has a continuous weighting function, whereas CNEL has a weighting function that varies in steps. Most of the traffic at this airport, especially during the exercise periods, occurs during the daytime hours, and the relative proportion of traffic during the morning and evening transition periods is low. For most practical purposes the EFN levels in this paper can therefore be considered the same as DNL. The EFN reference levels for a given airport are based on the actual traffic during the busiest four-week summer period. These EFN reference levels are used for noise zoning for land-use purposes.
223
The aircraft noise level outside each respondent’s home has been established by interpolating between noise contours calculated by the INM program. The noise levels have been recorded in 1 dB steps, but for averaging purposes the respondents have been grouped in 5 dB intervals. In the tables and diagrams, 53 EFN thus represents residents exposed to noise levels ranging from 51 EFN to 55 EFN and so on. A surprising result from this survey was that the best dose–response relationships were obtained by using the EFN reference levels as the noise parameters, not taking into account the extra noise load caused by increased traffic during the exercise periods. The traffic at this airport is fairly constant outside the exercise periods. The EFN reference levels therefore coincides with the average weekly noise levels. The noise levels reported in this paper always refer to the reference noise situation without any increased exercise activities. 4. RESULTS
At an early stage in the interview the respondents were asked to list things that they liked or disliked about their neighborhood. At that time there had been no reference by the interviewer to aircraft noise. One may assume that people who voluntarily mention dissatisfaction about aircraft noise are genuinely annoyed by this phenomenon. The combined results for all 3400 respondents are shown in Figure 1. In general, the dissatisfaction is low, and the respondents do not seem to be influenced by the large increase in aircraft activity during the exercises. February and August data represent the response just before the exercises which took place in March and September. Similarly, April and October data reflect the response just after the same exercises. March data are the response during the peak of the spring exercise but, unfortunately, no similar interview series were carried out during the fall exercise. The respondents were also asked directly: ‘‘Have you heard noise from aircraft while being at home the last month?’’ If the answer was positive, the following question was asked: ‘‘Would you consider this noise very annoying, quite annoying, a little annoying or not annoying?’’ The percentage who consider themselves ‘‘very annoyed’’ is shown in Figure 2. The response during each phase of the study turned out to be quite similar, and no significant changes in reaction could be detected.
Figure 1. The percentage of respondents who voluntarily mention that they dislike aircraft noise as a function 0 0 , April; <, August; < of the EFN reference level. q, February; ;, March; q ;, October. 0
224
. .
Figure 2. The percentage of respondents who consider themselves ‘‘very annoyed’’ by aircraft noise as a function of the EFN reference level. Key as Figure 1.
The effect of the March exercise was studied in detail by observing the shift in the response by the panel. These individuals were given identical questions throughout the study, and one can analyze directly how the response varies. The shift in response from February to March are shown in Figure 3. The figure illustrates the percentage of the panel members that considers the noise during the exercise less, equal to, or more annoying than the noise situation before the exercise. The upper solid line shows the sum of respondents considering the new noise situation less or equally annoying. Only about 20% regard the noise situation during the exercise more annoying than before, even though the increase in the daily noise exposure is as much as about 6 dB(A). At this particular airport military exercises normally occur twice per year. However, due to construction and refurbishing of the airfield, the March exercise was the first over a period of two years. The same lack of change in the response can be observed before and after the exercise in September, as illustrated in Figure 4. There is no indication that the high noise levels during the September maneuver have caused a noticeable shift in the assessment of noise annoyance. Also, in this case about 20% of the respondents regard the ‘‘after situation’’ most annoying, even though the two noise situations were almost identical. A similar
Figure 3. The average shift in the individual annoyance assessment. The graph shows the response during the March exercise compared with the response in February before to the exercise. ;, Less annoying; <, more annoying; q, equally annoying; —q—, sum less or equally annoying.
225
Figure 4. The average shift in the individual annoyance assessment. The graph shows the response after the September exercise compared with the response in August before the exercise. Key as in Figure 3.
number of respondents, however, regard the ‘‘after situation’’ as being less annoying. The percentage of respondents who change their subjective assessment of the noise situation, as shown in Figures 3 and 4, can therefore be regarded as a measure of uncertainty or indecision rather than as an expression of a real change in attitude toward the noise. An even clearer picture is derived by analyzing the total panel response to the question about aircraft noise annoyance the past month. The total response includes all the answers, not only the percentage ‘‘very annoyed’’. Scale values have been assigned to the response as follows: ‘‘very annoyed’’ = 1·00; ‘‘quite annoyed’’ = 0·67; ‘‘a little annoyed’’ = 0·33; ‘‘not annoyed’’ = 0·00. In Table 1 are shown the average total responses to the questions ‘‘Have you heard noise from aircraft while being at home the last month?’’ and, if the answer was ‘‘yes’’, ‘‘Would you consider this noise ‘‘very annoying, quite annoying, etc.?’’ The shift in response from one situation to another has been studied on an individual basis, using the same scale values for the verbal responses. In Table 2 are shown the mean difference for three selected combinations: Mar.–Feb., the response during the March exercise minus the response just before the exercise; Apr.–Feb., the response one month after the March exercise minus the response just before the exercise; Oct.–Aug., the response one month after the September exercise minus the response just before the exercise. The numbers in the tables are mean difference and standard deviation. Negative values indicate that the annoyance ‘‘before’’ is the larger quantity. The EFN reference level has been used as noise parameter.
T 1 Average annoyance scores; (mean and standard deviation for the annoyance scores for each series of interviews as a function of EFN reference aircraft noise level)
EFN 46–50 51–55 56–60 61–65 66–70
February ZXCXV A s 0·08 0·19 0·16 0·40 0·44
0·17 0·26 0·27 0·38 0·40
March ZXCXV A s 0·12 0·05 0·22 0·35 0·39
0·24 0·13 0·34 0·37 0·37
April ZXCXV A s 0·14 0·10 0·18 0·33 0·42
0·25 0·16 0·28 0·34 0·37
August ZXCXV A s 0·07 0·24 0·21 0·41 0·35
0·20 0·25 0·30 0·38 0·38
October ZXCXV A s 0·09 0·14 0·19 0·39 0·35
0·27 0·18 0·31 0·36 0·40
. .
226
T 2 Average differences in annoyance scores; (shift in annoyance score, mean and standard deviation, as a function of EFN reference aircraft noise level)
EFN
Mar.–Feb. ZXXCXXV A s
Apr.–Feb. ZXXCXXV A s
Oct.–Aug. ZXXCXXV A s
46–50 51–55 56–60 61–65 66–70
0·04 −0·14 0·07 −0·05 −0·05
0·18 0·18 0·33 0·31 0·38
0·06 −0·09 0·02 −0·07 −0·02
0·26 0·25 0·25 0·38 0·32
0·02 −0·09 −0·01 −0·05 0·00
0·28 0·25 0·27 0·34 0·46
Total
0·01
0·29
0·01
0·28
−0·01
0·32
5. DISCUSSION
The values in Table 1 indicate that even at the highest noise levels, 66 EFN to 70 EFN, the average resident is just slightly more than ‘‘a little annoyed’’ (=0·33) by aircraft noise. The average difference between the scores at the highest and lowest noise levels is 0·29. This corresponds to about 0·012 per dB for the range 46 EFN to 70 EFN. The average shift in the response from February to March as shown in Table 2, in other words, from a normal noise situation to a busy exercise period, is only 0·01 on the annoyance scale, corresponding to a change in noise levels of less than 1 dB. The actual change, however, was 6 dB. One can observe a similar slight shift when comparing the situation before and after the two exercise periods. If one assumes that the responses for each series of interviews have a normal distribution, a standard hypothesis test on means can be applied to the results. Such a test reveals that the probability that the response in March is different from the response in February is less than 50%; in other words, the two responses can be regarded as being equal. The same result applies to the two other conditions that have been presented in Table 2. One may argue that the stable response before, during and after an aircraft exercise period is governed by the high noise exposure during frequent exercises, and that the more quiet periods between these exercises do not contribute to the general annoyance assessment. The dose–response relationship for the reaction to noise around this airport has been calculated using the normal daily traffic as noise parameter, and omitting the extra traffic during the exercise periods. This dose–response relationship is very close to that derived by Schultz [1] in his synthesis of social surveys on community reactions to noise. One may therefore conclude that the reactions to the normal noise situation reported by residents around this airport are ‘‘normal’’; in other words, they do not differ from similar results reported from other studies. But why do the reactions in connection with the exercise periods not follow the same ‘‘normal’’ dose–response relationship? A respondent’s personal interest in the process that causes noise is believed to influence his assessment of the noise annoyance. A number of people in the community that has been studied have jobs either directly at the airport (military personnel and airline company employees) or have jobs that depend on the presence of the airport and the military base. The total data material was analyzed with respect to the respondent’s job situation. The response given by military personnel and people with jobs directly related to the airport
227
was compared with the response from people with non-airport related jobs. Contrary to what could be expected, the respondents in the first group (airport related) were slightly more annoyed than the others. However, the difference was not significant. The same tendency could be found for all five study periods. The missing influence by the increased noise exposure during the exercise can therefore not be explained by ‘‘personal interests’’. Another possible explanation for the abnormal response during the exercise could be that noise related parameters other than energy equivalent levels (or derivatives) are more important. Rylander et al. [2] have launched a theory that the annoyance is related to the maximum level if the number of aircraft noise events per day is about 50 or more. Due to changes in the fighter aircraft operations, the maximum levels experienced during the exercise are higher at any given EFN value; hence, according to Rylander, the annoyance should also be higher. The results presented in this report contradict this theory. There are large seasonal climatic differences in the northern part of Norway where this study was made. If the annoyance is mainly based on outdoor experience, one could hypothesize that the annoyance reported during the summer months would be larger. In the summer more time is spent outdoors, and windows are left open. A detailed analysis of the results presented in Table 1 show that no survey period is significantly different from the others. Seasonal differences can therefore not explain the abnormal response during the exercise. Some noise indices have taken the degree of level fluctuations into account: e.g., Noise Pollution Level, NPL [3]. NPL consists of two terms, one representing the equivalent continuous noise level on an energy basis, and the other representing the augmentation of annoyance due to level fluctuations. During the exercises the fluctuations in the noise level are larger than during normal traffic, as the flight patterns are different. An assessment of the noise annoyance based on the NPL index should yield an even higher degree of annoyance during the exercise. Our findings contradict this theory. Most models of community annoyance are essentially static models. Some of the most extensive data on the dynamic aspects of community annoyance come from a study by Fidell et al. [4]. They surveyed community reactions at four different time periods during changes in flight path operations at a local airport. One of their conclusions was as follows: ‘‘The prevalence of noise-induced annoyance in a community, does not react instantaneously to changes in exposure, nor does it fail to respond to changes in exposure that persist for periods of days, weeks or longer.’’ The second series of interviews in our study were made more than two weeks after the exercise in March had started. According to Fidell et al. [4], significant change in the reaction should be observed at that time. Our findings do not support this conclusion. 6. CONCLUSIONS
The community response to aircraft noise around this Norwegian airport seems very stable. When asked to assess the subjective annoyance caused by aircraft noise over the last month, the respondents did not seem to be affected by an increase in noise levels of the order of 6 dB caused by expanded aircraft operations during that particular period. On an annoyance scale ranging from zero to one, corresponding to ‘‘not annoyed’’ to ‘‘very annoyed’’, the average shift in response from a normal noise situation to a situation with 6 dB higher noise levels is only 0·01. This difference is not significant. When comparing the individual responses to these two situations, only about 20% of the respondents regard the ‘‘high noise’’ situation more annoying than the ‘‘low noise’’ situation, and a similar percentage has the opposite opinion. The response immediately before and after an exercise period with at least a 6 dB increase in the daily noise level is also constant. In this case
228
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also, about 20% of the respondents regard one situation more annoying than the other, and a similar percentage has the opposite opinion, even though these two situations were almost identical. This reaction was observed among more than 3000 naı¨ ve respondents and also among a panel of about 200 individuals that were monitored throughout the study period. ACKNOWLEDGMENTS
This study has been financed in full by the Norwegian Defense Construction Services, and the authors appreciate the enthusiastic support of their project contact, Jens-Jo rgen Bugge. James M. Fields: thank you, Jim, for sharing your knowledge and insight in studies of community reactions to noise [5]. The interviews have been conducted by the Norwegian Gallup Institute under the supervision of Svein Roar Hult. REFERENCES 1. T. J. S 1978 Journal of the Acoustical Society of America 64(2), 377–405. Synthesis of social surveys on noise annoyance. 2. R. R, M. B and S. S 1993 Proceedings of the 6th Congress of the International Committee on Biological Effects of Noise, Nice, France, July 1993. Dose–response relationships for environmental noises. 3. D. W. R 1971 Journal of Sound and Vibration 14, 279–298. Towards a unified system of noise assessment. 4. S. F, R. H, J. M, E. B, S. T and K. P 1985 Journal of the Acoustical Society of America 77(3), 1054–1068. Aircraft noise annoyance at three joint air carrier and general aviation airports. 5. T. G, K. H. L , I. L. N. G and J. M. F 1990 SINTEF DELAB Report STF40 A90189. Response to noise around Oslo Airport Fornebu.
COMMUNITY RESPONSE TO NOISE FROM SHORT-TERM MILITARY AIRCRAFT EXERCISE T. G, K. H. L I. L. N. G SINTEF DELAB, N-7034 Trondheim, Norway (Received 4 November 1993, and in final form 14 February 1994) A study of community reactions to noise in the vicinity of a Norwegian airport has been conducted in connection with two large military exercises. An extensive questionnaire was presented to a random sample of residents before, during and after each exercise. More than 3400 interviews were completed. The group of respondents also contained a panel of about 200 people who were given identical questions in each survey series. This paper presents the results with an emphasis on the data from this panel. The results indicate that the general reaction to aircraft noise is not altered by short periods with increased noise exposure.
1. BACKGROUND
A number of Norwegian airports serve both civil and military traffic, and occasionally these airports are used for military aircraft exercise purposes. The exercises include operations by fighters, helicopters and transport aircraft, and during these periods the total number of daily operations increases considerably with a corresponding shift in the noise exposure. The environmental impact on the community in the vicinity of these airports thus changes dramatically, and there is a potential chance that the community reaction to aircraft noise changes in a negative direction. An extensive study of community reactions to aircraft noise has been conducted in the vicinity of a Norwegian airport that serves both civil and military traffic. Two large military exercises took place in the study period. During these exercises the number of aircraft operations increased significantly, and the total noise exposure increased by about 6 dB for a period of 2–3 weeks. Social surveys were conducted before, during and after these exercises and more than 3400 interviews were completed. The respondents were mainly naı¨ ve residents, but a panel of about 200 persons was also established. These 200 persons were interviewed throughout the study period. Their responses were recorded on an individual basis, so that the data can be analyzed with respect to changes in the response for each single panel member.
2. STUDY DESIGN
The exercises took place in March and September 1992. Telephone interviews were conducted before, during and after the first exercise, and before and after the second exercise. Noise measurements and radar tracking of the air traffic were carried out in order to obtain a precise description of the total noise exposure. About 500 naı¨ ve respondents participated in each series of interviews, together with a panel of about 200. 221 0022–460X/95/170221 + 08 $08.00/0
7 1995 Academic Press Limited
222
. .
A list of all private telephone subscribers in the area was supplied by the local telephone company. The subscribers were sorted into different groups according to their normal noise exposure, each group covering a range of 5 dB(A) corresponding to established ‘‘noise zones’’. Within each group a random selection of telephone numbers to call during each series was made. The number of subscribers in each group was sufficiently large to obtain the desired sample size after adjusting for refusals and other types of non-response. In each subscriber household the interviewer asked to interview whichever resident would be the next to have a birthday. Respondents were required to be more than 15 years of age. Repeated calls (four or five times) were made if the selected individual was not initially available. At the end of the initial interview, the respondent was asked if he or she would be willing to participate in future study series; in other words, to be part of a survey panel. Those who volunteered were identified by name, so that the right individual could be located for the next series. A panel of 200 respondents was randomly selected from this group. The questionnaire was presented as a general survey of neighborhood condition, and also contained a number of demographic and other non-aircraft related issues. The results from the different survey periods were analyzed with respect to any shift in reaction due to changes in the aircraft operations. The main questions were as follows: Can the dose–response relationship established for the normal situation also be applied to an exercise period? Is there an ‘‘over-reaction’’ caused by large changes in the noise exposure? 3. NOISE SITUATION
The regular air traffic at this particular airport consists of about 140 civil and 70 military movements per day (take-offs or landings). During the exercise periods the number of military movements increased to about 130 per day and at the same time the civil traffic was reduced to 110. The regular civil traffic consists of 16% jet, 60% turboprop, 22% single and twin engine GA propeller traffic, and 2% helicopters. The military traffic consists of 69% fighter aircraft, 18% transporter aircraft and 13% helicopters. The noise levels in the area have been recorded and compared with results from the INM Aircraft Noise Calculation Program, using the actual air traffic as input. The INM Program, initially developed by the US Federal Aviation Administration, is used to calculate noise zones for land-use purposes around Norwegian airports. The difference between the actual measurements and the calculated noise levels were small, typically 1–2 dB(A). Calculated noise levels have therefore been used for the remainder of this paper. Norway has adopted a special aircraft noise index called EFN, the Equivalent Aircraft Noise Level. This is an energy equivalent time weighted noise index. Noise events during the night period are penalized by a factor of ten (equal to 10 dB), while noise events during the morning and evening transition periods are penalized with graduated weight. Noise events on Sundays are penalized by a factor of three (5 dB). EFN resembles the Community Noise Equivalent Level, CNEL. The only difference is that EFN has a continuous weighting function, whereas CNEL has a weighting function that varies in steps. Most of the traffic at this airport, especially during the exercise periods, occurs during the daytime hours, and the relative proportion of traffic during the morning and evening transition periods is low. For most practical purposes the EFN levels in this paper can therefore be considered the same as DNL. The EFN reference levels for a given airport are based on the actual traffic during the busiest four-week summer period. These EFN reference levels are used for noise zoning for land-use purposes.
223
The aircraft noise level outside each respondent’s home has been established by interpolating between noise contours calculated by the INM program. The noise levels have been recorded in 1 dB steps, but for averaging purposes the respondents have been grouped in 5 dB intervals. In the tables and diagrams, 53 EFN thus represents residents exposed to noise levels ranging from 51 EFN to 55 EFN and so on. A surprising result from this survey was that the best dose–response relationships were obtained by using the EFN reference levels as the noise parameters, not taking into account the extra noise load caused by increased traffic during the exercise periods. The traffic at this airport is fairly constant outside the exercise periods. The EFN reference levels therefore coincides with the average weekly noise levels. The noise levels reported in this paper always refer to the reference noise situation without any increased exercise activities. 4. RESULTS
At an early stage in the interview the respondents were asked to list things that they liked or disliked about their neighborhood. At that time there had been no reference by the interviewer to aircraft noise. One may assume that people who voluntarily mention dissatisfaction about aircraft noise are genuinely annoyed by this phenomenon. The combined results for all 3400 respondents are shown in Figure 1. In general, the dissatisfaction is low, and the respondents do not seem to be influenced by the large increase in aircraft activity during the exercises. February and August data represent the response just before the exercises which took place in March and September. Similarly, April and October data reflect the response just after the same exercises. March data are the response during the peak of the spring exercise but, unfortunately, no similar interview series were carried out during the fall exercise. The respondents were also asked directly: ‘‘Have you heard noise from aircraft while being at home the last month?’’ If the answer was positive, the following question was asked: ‘‘Would you consider this noise very annoying, quite annoying, a little annoying or not annoying?’’ The percentage who consider themselves ‘‘very annoyed’’ is shown in Figure 2. The response during each phase of the study turned out to be quite similar, and no significant changes in reaction could be detected.
Figure 1. The percentage of respondents who voluntarily mention that they dislike aircraft noise as a function 0 0 , April; <, August; < of the EFN reference level. q, February; ;, March; q ;, October. 0
224
. .
Figure 2. The percentage of respondents who consider themselves ‘‘very annoyed’’ by aircraft noise as a function of the EFN reference level. Key as Figure 1.
The effect of the March exercise was studied in detail by observing the shift in the response by the panel. These individuals were given identical questions throughout the study, and one can analyze directly how the response varies. The shift in response from February to March are shown in Figure 3. The figure illustrates the percentage of the panel members that considers the noise during the exercise less, equal to, or more annoying than the noise situation before the exercise. The upper solid line shows the sum of respondents considering the new noise situation less or equally annoying. Only about 20% regard the noise situation during the exercise more annoying than before, even though the increase in the daily noise exposure is as much as about 6 dB(A). At this particular airport military exercises normally occur twice per year. However, due to construction and refurbishing of the airfield, the March exercise was the first over a period of two years. The same lack of change in the response can be observed before and after the exercise in September, as illustrated in Figure 4. There is no indication that the high noise levels during the September maneuver have caused a noticeable shift in the assessment of noise annoyance. Also, in this case about 20% of the respondents regard the ‘‘after situation’’ most annoying, even though the two noise situations were almost identical. A similar
Figure 3. The average shift in the individual annoyance assessment. The graph shows the response during the March exercise compared with the response in February before to the exercise. ;, Less annoying; <, more annoying; q, equally annoying; —q—, sum less or equally annoying.
225
Figure 4. The average shift in the individual annoyance assessment. The graph shows the response after the September exercise compared with the response in August before the exercise. Key as in Figure 3.
number of respondents, however, regard the ‘‘after situation’’ as being less annoying. The percentage of respondents who change their subjective assessment of the noise situation, as shown in Figures 3 and 4, can therefore be regarded as a measure of uncertainty or indecision rather than as an expression of a real change in attitude toward the noise. An even clearer picture is derived by analyzing the total panel response to the question about aircraft noise annoyance the past month. The total response includes all the answers, not only the percentage ‘‘very annoyed’’. Scale values have been assigned to the response as follows: ‘‘very annoyed’’ = 1·00; ‘‘quite annoyed’’ = 0·67; ‘‘a little annoyed’’ = 0·33; ‘‘not annoyed’’ = 0·00. In Table 1 are shown the average total responses to the questions ‘‘Have you heard noise from aircraft while being at home the last month?’’ and, if the answer was ‘‘yes’’, ‘‘Would you consider this noise ‘‘very annoying, quite annoying, etc.?’’ The shift in response from one situation to another has been studied on an individual basis, using the same scale values for the verbal responses. In Table 2 are shown the mean difference for three selected combinations: Mar.–Feb., the response during the March exercise minus the response just before the exercise; Apr.–Feb., the response one month after the March exercise minus the response just before the exercise; Oct.–Aug., the response one month after the September exercise minus the response just before the exercise. The numbers in the tables are mean difference and standard deviation. Negative values indicate that the annoyance ‘‘before’’ is the larger quantity. The EFN reference level has been used as noise parameter.
T 1 Average annoyance scores; (mean and standard deviation for the annoyance scores for each series of interviews as a function of EFN reference aircraft noise level)
EFN 46–50 51–55 56–60 61–65 66–70
February ZXCXV A s 0·08 0·19 0·16 0·40 0·44
0·17 0·26 0·27 0·38 0·40
March ZXCXV A s 0·12 0·05 0·22 0·35 0·39
0·24 0·13 0·34 0·37 0·37
April ZXCXV A s 0·14 0·10 0·18 0·33 0·42
0·25 0·16 0·28 0·34 0·37
August ZXCXV A s 0·07 0·24 0·21 0·41 0·35
0·20 0·25 0·30 0·38 0·38
October ZXCXV A s 0·09 0·14 0·19 0·39 0·35
0·27 0·18 0·31 0·36 0·40
. .
226
T 2 Average differences in annoyance scores; (shift in annoyance score, mean and standard deviation, as a function of EFN reference aircraft noise level)
EFN
Mar.–Feb. ZXXCXXV A s
Apr.–Feb. ZXXCXXV A s
Oct.–Aug. ZXXCXXV A s
46–50 51–55 56–60 61–65 66–70
0·04 −0·14 0·07 −0·05 −0·05
0·18 0·18 0·33 0·31 0·38
0·06 −0·09 0·02 −0·07 −0·02
0·26 0·25 0·25 0·38 0·32
0·02 −0·09 −0·01 −0·05 0·00
0·28 0·25 0·27 0·34 0·46
Total
0·01
0·29
0·01
0·28
−0·01
0·32
5. DISCUSSION
The values in Table 1 indicate that even at the highest noise levels, 66 EFN to 70 EFN, the average resident is just slightly more than ‘‘a little annoyed’’ (=0·33) by aircraft noise. The average difference between the scores at the highest and lowest noise levels is 0·29. This corresponds to about 0·012 per dB for the range 46 EFN to 70 EFN. The average shift in the response from February to March as shown in Table 2, in other words, from a normal noise situation to a busy exercise period, is only 0·01 on the annoyance scale, corresponding to a change in noise levels of less than 1 dB. The actual change, however, was 6 dB. One can observe a similar slight shift when comparing the situation before and after the two exercise periods. If one assumes that the responses for each series of interviews have a normal distribution, a standard hypothesis test on means can be applied to the results. Such a test reveals that the probability that the response in March is different from the response in February is less than 50%; in other words, the two responses can be regarded as being equal. The same result applies to the two other conditions that have been presented in Table 2. One may argue that the stable response before, during and after an aircraft exercise period is governed by the high noise exposure during frequent exercises, and that the more quiet periods between these exercises do not contribute to the general annoyance assessment. The dose–response relationship for the reaction to noise around this airport has been calculated using the normal daily traffic as noise parameter, and omitting the extra traffic during the exercise periods. This dose–response relationship is very close to that derived by Schultz [1] in his synthesis of social surveys on community reactions to noise. One may therefore conclude that the reactions to the normal noise situation reported by residents around this airport are ‘‘normal’’; in other words, they do not differ from similar results reported from other studies. But why do the reactions in connection with the exercise periods not follow the same ‘‘normal’’ dose–response relationship? A respondent’s personal interest in the process that causes noise is believed to influence his assessment of the noise annoyance. A number of people in the community that has been studied have jobs either directly at the airport (military personnel and airline company employees) or have jobs that depend on the presence of the airport and the military base. The total data material was analyzed with respect to the respondent’s job situation. The response given by military personnel and people with jobs directly related to the airport
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was compared with the response from people with non-airport related jobs. Contrary to what could be expected, the respondents in the first group (airport related) were slightly more annoyed than the others. However, the difference was not significant. The same tendency could be found for all five study periods. The missing influence by the increased noise exposure during the exercise can therefore not be explained by ‘‘personal interests’’. Another possible explanation for the abnormal response during the exercise could be that noise related parameters other than energy equivalent levels (or derivatives) are more important. Rylander et al. [2] have launched a theory that the annoyance is related to the maximum level if the number of aircraft noise events per day is about 50 or more. Due to changes in the fighter aircraft operations, the maximum levels experienced during the exercise are higher at any given EFN value; hence, according to Rylander, the annoyance should also be higher. The results presented in this report contradict this theory. There are large seasonal climatic differences in the northern part of Norway where this study was made. If the annoyance is mainly based on outdoor experience, one could hypothesize that the annoyance reported during the summer months would be larger. In the summer more time is spent outdoors, and windows are left open. A detailed analysis of the results presented in Table 1 show that no survey period is significantly different from the others. Seasonal differences can therefore not explain the abnormal response during the exercise. Some noise indices have taken the degree of level fluctuations into account: e.g., Noise Pollution Level, NPL [3]. NPL consists of two terms, one representing the equivalent continuous noise level on an energy basis, and the other representing the augmentation of annoyance due to level fluctuations. During the exercises the fluctuations in the noise level are larger than during normal traffic, as the flight patterns are different. An assessment of the noise annoyance based on the NPL index should yield an even higher degree of annoyance during the exercise. Our findings contradict this theory. Most models of community annoyance are essentially static models. Some of the most extensive data on the dynamic aspects of community annoyance come from a study by Fidell et al. [4]. They surveyed community reactions at four different time periods during changes in flight path operations at a local airport. One of their conclusions was as follows: ‘‘The prevalence of noise-induced annoyance in a community, does not react instantaneously to changes in exposure, nor does it fail to respond to changes in exposure that persist for periods of days, weeks or longer.’’ The second series of interviews in our study were made more than two weeks after the exercise in March had started. According to Fidell et al. [4], significant change in the reaction should be observed at that time. Our findings do not support this conclusion. 6. CONCLUSIONS
The community response to aircraft noise around this Norwegian airport seems very stable. When asked to assess the subjective annoyance caused by aircraft noise over the last month, the respondents did not seem to be affected by an increase in noise levels of the order of 6 dB caused by expanded aircraft operations during that particular period. On an annoyance scale ranging from zero to one, corresponding to ‘‘not annoyed’’ to ‘‘very annoyed’’, the average shift in response from a normal noise situation to a situation with 6 dB higher noise levels is only 0·01. This difference is not significant. When comparing the individual responses to these two situations, only about 20% of the respondents regard the ‘‘high noise’’ situation more annoying than the ‘‘low noise’’ situation, and a similar percentage has the opposite opinion. The response immediately before and after an exercise period with at least a 6 dB increase in the daily noise level is also constant. In this case
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also, about 20% of the respondents regard one situation more annoying than the other, and a similar percentage has the opposite opinion, even though these two situations were almost identical. This reaction was observed among more than 3000 naı¨ ve respondents and also among a panel of about 200 individuals that were monitored throughout the study period. ACKNOWLEDGMENTS
This study has been financed in full by the Norwegian Defense Construction Services, and the authors appreciate the enthusiastic support of their project contact, Jens-Jo rgen Bugge. James M. Fields: thank you, Jim, for sharing your knowledge and insight in studies of community reactions to noise [5]. The interviews have been conducted by the Norwegian Gallup Institute under the supervision of Svein Roar Hult. REFERENCES 1. T. J. S 1978 Journal of the Acoustical Society of America 64(2), 377–405. Synthesis of social surveys on noise annoyance. 2. R. R, M. B and S. S 1993 Proceedings of the 6th Congress of the International Committee on Biological Effects of Noise, Nice, France, July 1993. Dose–response relationships for environmental noises. 3. D. W. R 1971 Journal of Sound and Vibration 14, 279–298. Towards a unified system of noise assessment. 4. S. F, R. H, J. M, E. B, S. T and K. P 1985 Journal of the Acoustical Society of America 77(3), 1054–1068. Aircraft noise annoyance at three joint air carrier and general aviation airports. 5. T. G, K. H. L , I. L. N. G and J. M. F 1990 SINTEF DELAB Report STF40 A90189. Response to noise around Oslo Airport Fornebu.