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|Year : 2000 | Volume
| Issue : 9 | Page : 59--71
Physiological, subjective, and behavioural responses during sleep to noise from rail and road traffic
Barbara Griefahn, Anke Schuemer-Kohrs, Rudolf Schuemer, Ulrich Moehler, Peter Mehnert
Institute for Occupational Physiology at the University of Dortmund, Dortmund, Fed. Rep., Germany
Institute for Occupational Physiology at the University of Dortmund, Ardeystr. 67, D-44139 Dortmund, Fed. Rep.
An interdisciplinary study was performed to examine the difference between road and rail traffic noise with regard to physiological, subjective, and behavioral responses. In 8 areas where either rail or road noise prevailed, a total of 1 600 persons (18 to 70 years of age) were interviewed; a subgroup of 377 persons was examined during 2 times 5 nights each. In this sleep observation period noise impact and body movements were recorded continuously during each night. Every morning the subjects stated the position of the windows during the night, they evaluated the qualitative and quantitative parameters of sleep and performed a 4-choice reaction time test. Only the behavior to sleep with open or closed windows was significantly associated with the rating level and the windows were significantly more often closed by the residents primarily exposed to road noise. Whether this indicates a reaction to noise or to concomitant pollutants such as odour is, however, debatable. The fact that none of the other data recorded here revealed any difference between the two types of noise is discussed in view of future studies.
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Griefahn B, Schuemer-Kohrs A, Schuemer R, Moehler U, Mehnert P. Physiological, subjective, and behavioural responses during sleep to noise from rail and road traffic.Noise Health 2000;3:59-71
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Griefahn B, Schuemer-Kohrs A, Schuemer R, Moehler U, Mehnert P. Physiological, subjective, and behavioural responses during sleep to noise from rail and road traffic. Noise Health [serial online] 2000 [cited 2021 Jul 24 ];3:59-71
Available from: https://www.noiseandhealth.org/text.asp?2000/3/9/59/31769
Regarding environmental factors, which interfere with human activities, people complain most frequently about noises that are emitted by air traffic, by road and by rail traffic [Berglund & Lindvall 1995, Hume & Thomas 1993]. Residents living near airports, in streets with high traffic density, and along railway tracks complain most often about interference with speech communication, whereas noise-induced sleep disturbances are less frequent but regarded as most deleterious. In a most global sense sleep disturbances are defined as any measurable or subjectively experienced alteration of usual (and even desired) sleep behaviour. They vary accordingly in a large range and comprise vegetative responses, body movements, transient alterations of the electroencephalogram (such as K-complexes), decreases of sleep depth, intermittent and premature awakenings as well as prevention of sleep either in the evening or after intermittent awakenings [Griefahn 1985]. The longer the involuntary periods awake and the more difficult it is to fall asleep or to return to sleep the more likely these states are recalled in the morning, they then determine subjective sleep quality, mood, actual well-being and performance. In the long run, this stress is assumed to contribute to the genesis of chronic health disorders, particularly of cardiovascular diseases [Ising et al. 1997]. As traffic density will grow in Europe by about 80 % until the year 2 010, more during the night than during the day sleep disturbances are expected to increase as well [Griinbuch der EU 1996].
Research on noise-induced sleep disturbances either in the laboratory or in the field was mainly focused to noises from air traffic and from road traffic; noises emitted from railways were studied rather seldom [Griefahn 1978, Hofmann et al. 1993, Vernet 1983].
A few social surveys were directed to the comparison of noises from road and rail traffic. These investigations concerned primarily annoyance during daytime where only a very few questions concerned sleep. The respective studies revealed that the same noise levels are less annoying in areas with prevailing rail traffic than in areas with dominating road traffic [Fields & Walker 1982, Miedema 1998, Moehler 1988]. So, in several countries the admissible limits are higher for railway noises than for noises from road traffic. In the Federal Republic of Germany, for instance, a 'bonus' for rail noise was set to 5 dBA for daytime and for nighttime as well. The validity of this advantage for rail noise with regard to sleep behaviour is, however, debated as it is not based on direct observations of sleep.
A field study is concerned as appropriate to evaluate the difference between road and rail traffic noise with regard to physiological, subjective, and behavioral responses. This presupposes the observation of sufficiently large samples and sufficiently long observation periods as sleep behaviour in the real situation is usually determined by numerous greatly varying sound pressure levels and sleep behaviour is influenced by numerous exogenic and endogenic factors. Therefore, an interdisciplinary team of acousticians, psychologists, and physiologists scrutinized the assumed differences of the effects as caused by rail and by road noise while observing numerous people usually exposed to either prevailing rail or road traffic noise.
The temporal structures of road and rail noises differ considerably. Road traffic causes rather continuous noises which are additionally characterised by a decrease between 12 pm and 4 am, where rail noise is clearly intermittent but equally distributed over the 24 hours of the day. Based on previous studies the following 2, rather contradictory hypotheses must be considered: - Rail noise disturbs more due to its intermittent character [e.g. Griefahn 1992, Ohrstrom & Rylander 1982, Vallet et al. 1983]. - Road noise disturbs more because it annoys more during the day and because the human brain is able to recognise properly and to respond adequately to acoustic stimuli even while asleep [e.g. Strauch et al 1976].
Materials and Methods
The study was executed in 3 phases, where the main part consisted of the sleep observation period, where overall 377 persons were studied during a period of 2 times 5 nights each. These observations and the preceding social survey were executed during spring and autumn in order to avoid alterations of sleep behaviour due to extreme cold or hot climates that might occur in the summer or in the winter [Natani & Shurley 1973, Otto 1973].
Phase 1: Selection of suitable areas. Based on traffic density maps for roads and for rail tracks the acousticians estimated the noise levels and determined areas which were similar with respect to buildings and residents (some selection criteria are listed in [Table 1]. After the acoustical estimations were completed, preselected areas were then inspected by acousticians, psychologists, and physiologists and accepted or refuted for the study [Moehler et al. 1998]. Eventually, 2 times 4 areas were selected with either prevailing road or rail traffic but similar with respect to noise levels, buildings, social, and demographic characteristics of the residents.
Phase 2: Social survey. The acoustical calculations and the social survey were executed by a team that was already involved in a comparative study executed in the early eighties [IF-Study II 1983, Moehler et al. 1986, Schuemer & Schuemer-Kohrs 1991]. Based on the experience of this study and on actual knowledge an extended questionnaire was developed. The questionnaire comprised personal data, actual health state, occupation, housing conditions, and residential area. The most extended part concerned environmental noise (sensitivity, annoyance, attitudes, noise abatement etc.) and sleeping habits (bedtimes, position of windows etc.). A 5-point scale was applied for most answers. The interviews were executed with 1 600 randomly selected persons shortly before the sleep observation period and lasted about 45 minutes. To achieve a large range of sound pressure levels for the determination of dose-response relations and for the assessment of the assumed differences between road and rail noise the homes of the participants were spread over a large area and had varying distances from the dominant noise source. Some selection criteria are listed in [Table 1].
Phase 3: Sleep Observation Period. At the end of the interviews, the subjects were asked to participate in the sleep observation period. They filled in a special questionnaire which concerned their health state. Habitual consumers of sleeping pills and those with chronic diseases that might interfere with sleep were excluded. The recordings comprised the registration of body movements, the daily assessment of the actual situation and of sleep as well as a performance test. The instruments were distributed every evening and collected the next morning. The data of the acetimeters and of the performance tests were daily checked and saved. Participants: 377 persons, 18 - 66 years of age, equally distributed with respect to the quality and quantity of noise exposure and to gender were observed in their usual environment during 2 times 5 nights each, from Sunday evening to Friday morning (some characteristics are listed in [Table 2]. The weekends were disregarded as the quality and quantity of noise as well as sleep behaviour then differ considerably (trucks then are not allowed and people go to bed later).
Acoustical data. The acoustical data were continuously recorded during each night at the dominant noise source (rail track, road), during one night also in the bedrooms and outdoors in front of the bedroom windows. For each night the source-specific noise level (road or rail) was calculated for each individual i.e. the levels as if measured outdoors in front of the window of the bedroom and the levels as if measured indoors in the bedroom (for more details see Liepert et al. 1997).
Movements, actigrams. Actimeters (Gahwiler) which were tied to the wrist of the participants were applied to indicate body movements as a substitute for awakenings. The latter are usually accompanied by body movements. The thresholds for noise-induced body movements are lower than for awakenings, but their densities and durations are greater during awake than during sleep. (To quantify this, the electrophysiological parameters of sleep (EEG, EOG, EMG) were recorded from 238 subjects during one night simultaneously with the actigram.) The sample rates of the actimeters which were previously applied in a field study on the effects of aircraft noise on sleep in the UK [Ollerhead et al. 1992] were set to 2-s-epochs thus allowing an exact determination of the densities and the durations of movements.
Questionnaire. The participants completed short questionnaires every evening and every morning to assess the actual situation and the qualitative and quantitative parameters of sleep. The morning questionnaire comprised tension, tiredness, bedtime, subjective sleep quality, intermittent awakenings, and position of the windows, the evening questionnaire comprised actual tension and tiredness, physical, mental and emotional stress, tension and tiredness during the day, consumption of alcohol or drugs. Performance test. A 4-choice test was executed during one week, again every evening and every morning. The test which allows to determine the quality and quantity of performance (errors, speed) was basically a conventional 4-choice reaction time test, where one out of 4 LEDs arranged in a square lights up randomly. After one out of four keys below the LEDs was pressed, the next signal occurred after a defined delay. The maximum time span for a reaction was constant during the first 3 minutes and varied according to the percentage of errors during the last 2 minutes. To achieve a constant error rate of 30 %, the speed was lowered in case of higher rates and accordingly increased in case of lower rates (time spans were prolonged respectively reduced).
Behaviour: Every morning the participants had to state in their questionnaire, whether they had slept with windows wide open, half open or closed.
Statistics: Several statistical procedures were applied. Apart from t-tests for dependent and for independent samples, Chi-square tests, Wilcoxon tests etc. factor analyses were completed to condense the data recorded with the morning questionnaire. For the assessment of noise related effects the Generalised Linear Model was applied.
Noise stress. The equivalent sound pressure levels [Figure 1] emitted from road traffic revealed a decrease during the early night and an increase towards the end of the night, where noise from railway traffic remained constant. Calculated nocturnal outdoor noise levels (Lm, 10 pm to 8 am) 1 m in front of the bedrooms, varied between 36 and 78 dBA, between 36 and 76 dBA for rail and between 40 and 68 dBA for road noise [see Moehler et al. 1998].
Social surveys: The main goal of the present study was to scrutinize the assumed difference between rail and road noise particularly for the night. The social survey was designed to prove this for the daytime as well, but the data presented here are restricted to the items of the questionnaire that concerned noise-related disturbances during the night. The results are summarized in [Table 3]. Using the General linear regression model the differences between both types of noises were calculated for each of the respective items for 50 and for 70 dBA as well. The data suggest that the effects of road and rail noise are comparable in case that the latter, namely rail noise is 8 to almost 20 dBA higher than road noise. The difference is lowest for falling asleep and highest for premature awakenings.
Sleep observation period: Regarding body movements, subjective assessment of qualitative and quantitative parameters of sleep as well as the quantity and quality of test performance, none of these variables revealed any statistically significant relation to any of the acoustical data, neither for the whole night nor for the single events (type of noise, number of noise events, sound pressure levels, i.e. Lm, L1, L5 , L1-95 etc.).
Behaviour: The participants stated every morning whether they had slept with windows wide open, half open or closed. As the window position 'wide open' was stated only for a very few nights this variable was dichotomized to 'open' and 'closed' (coded as 1 and 0). [Figure 2] presents the relation between the position of the windows with the source-specific outdoor sound pressure level (as if measured 1 m before the bedroom window). Residents primarily exposed to road noise slept significantly less often with open windows than residents living along railway tracks as described in former studies [Moehler 1987]. To prove the goodness of fit of the model the data were additionally aggregated and plotted in steps of 10 dBA. These data support clearly the different behaviour of residents living in areas where either road or rail traffic prevailed.
In terms of statistical associations the position of the windows was the only variable (apart from the annoyance / disturbance variables from the social survey) that was strongly related to the noise level. Residents primarily exposed to road noise closed their bedroom windows significantly more often with increasing noise levels and significantly more often than the residents living along railway tracks. It is, however, debatable, whether this can be related to noise or whether another concomitant pollutant such as odour is the underlying cause for that behaviour.
Apart from the window position, no other variable, neither physiological, nor subjective or behavioral was significantly related to the noise level and this was true even after numerous moderator variables were regarded in the respective statistical models (gender, age, sensitivity, liability etc.). This is in accordance with other recently executed field studies on aircraft noises [Fidell et al. 1995, 1998, Horne et al. 1994, Pearsons et al. 1995]. The results, however, reveal a great discrepancy to laboratory studies, where even extremely low levels evoked sleep disorders and where the extents of the effects increased with the sound pressure levels [e.g. Thiessen 1978]. On the other hand, it is not unlikely that the effects which were observed in the laboratory were enhanced by the strictly controlled and unfamiliar situation whereas man adapts undoubtedly more or less quickly to his usual environment. However, even then full habituation in the sense that no response occurs anymore, is not likely. Instead, it is reasonable to assume that the effects then are masked by various individual and situational factors. This should be discussed particularly in view of the design of future studies.
Methodological aspects: The first considerations, however, concern the methods applied.
Actimeters: The registration of body movements is a method which was applied in this particular field of research since many years [e.g. Ohrstrom & Rylander 1982] and which is nowadays mostly used for field research on the effects of aircraft noise and road traffic noise [e.g. Fidell et al. 1998, Passchier-Vermeer et al., 1999, Ohrstrom 1999]. The actimeters used here were previously applied in a field study on the effects of aircraft noise on sleep in the UK and validated and calibrated for this particular purpose [Horne et al. 1994]. They are less sensitive than the electrophysiological measures (EEG: electroencephalogram, EOG: electrooculogram, EMG: electromyogram) but the comparison with the latter revealed that at least 85 % of the awakenings were detected by means of this method.
The actimeters register accelerations of at least 0.1 g continuously throughout the night. To assess their sensitivity and reliability these instruments were repeatedly exposed to defined vibrations (sine waves of different frequencies and accelerations presented in the vertical and/or in the horizontal direction). Though sensitivity varied in a larger range than stated by the producer, extensive measures revealed that this was rather irrelevant for the present study as body movements during awake are (fortunately) usually executed with accelerations well above 0.1 g. So, body movements were registered with sufficient reliability irrespective of the sensitivity of the actimeters. A sufficient reliability was furthermore indicated by significant correlations of the data registered in comparable nights (nights from Tuesday to Wednesday of the 1st and the 2nd week of the sleep observation period) and between the times of sleep onset and offset as determined by the actimeters and estimated by the participants (onset = 0.89, offset = 0.97, p Self-estimated quantity and quality of sleep:
Noise did not influence the subjective evaluation of sleep. This is well in accordance with other field studies [Fidell et al. 1998, Horne et al. 1994, Pearsons et al. 1995] but different to those studies where the subjects slept under the influence of varied sound pressure levels [Griefahn & Gros 1986, Griefahn 1991]. The reason might be that the subjects once adapted to a scarcely varying environment, developed and applied their individual standard and estimated their actual sleep in relation to their usual sleep behaviour. If so, there is on the one hand a need for questionnaires which refer to external, generally acceptable standards and on the other hand this suggests an experimental intervention, particularly the experimental variation of the sound pressure levels for one or several nights. Apart from this, frequently reported relations were again verified (age, eveningness, liability etc.) thus indicating the validity of the questionnaire.
On the contrary, the interviews executed during the preceding social survey revealed a clear difference between road and rail noise of at least 8 dBA. The decisive difference between these interviews and the daily sleep logs completed in the sleep observation period was probably that the questions asked in the interviews stressed to noise-induced nocturnal disturbances where this was avoided in the daily sleep logs. As the actual acoustical situation during the interview might have influenced these evaluations, this discrepancy can - with respect to the fact that the majority of interviews were executed during leisure time - hint to a particular vulnerability during recreation time.
Performance: Neither the speed nor the percentage of errors determined with the 4choice test were influenced by noise. This contradicts several other studies where test performance was impaired though never dramatically [Ohrstrom & Rylander 1982, Griefahn 1986]. A reasonable explanation might be that each individual in the respective studies slept under the influence of different sound pressure levels where the noise load in the present study varied for one and the same individual by not more than 2.5 dBA. The 4choice test applied here was on the other hand a valid method as previously reported relations were again verified such as variations of performance due to age, tiredness, and self estimated sleep depth. Here again, an intervention, i.e. an experimental variation of the sound pressure level could have been advantageous.
Individual and situational influences
In summary, it seems unlikely that the methods applied are not appropriate. On the other hand, it is premature to assume complete habituation. Instead, it is essential to consider the great variety of (competitive) influences that are individual factors which may increase a person's resistance or vulnerability against external stimuli and situational, simultaneously acting factors with antagonistic or synergistic effects.
Habituation: Though some residents probably develop full adaptation, this is not likely for the whole sample. Several authors observed a decrease but no extinction of noise-induced reactions for people living in noisy areas. Even residents exposed to vivid road traffic for many years revealed fewer sleep disturbances if sound pressure levels are reduced [Vallet et al. 1983]. In the present study a rather paradoxical effect pretending habituation might have occurred due to the high number of noise events. Previous quantitative analyses of the literature and suitable experimental studies in the laboratory revealed that the risk to be awakened by a single noise event decreases with the number of stimuli [Griefahn 1985, Muzet 1980]. Though noise-induced awakenings might disappear completely, overall sleep depth may become flatter and the sympathetic tone may increase accordingly. If so, the collection of urine to measure cortisole and catecholamines as e.g. done by Maschke et al. (1997) and by Ising et al. (1990) seems to be reasonable. However, as these alterations are unspecific and evoked by many other personal and environmental influences the respective results can be interpreted unequivocally only if caused in strictly controlled situations.
Sleep duration: Another possible reason for the lack of responses might be that sleep durations were much shorter than reported in the literature (6:45 hours). So, it is not unlikely that the participants slept already at their lower limit (obligatory sleep) where the thresholds for external stimuli rise accordingly.
Competitive effects: Two competitive hypotheses were formulated for this investigation. If both are true, namely that the effects of road noise are determined by higher annoyance level and the effects of rail noise by its intermittent occurrence the extent of the effects might be rather the same for both noises. Noise: Noise was measured at the dominant noise source, either at roads or at rail tracks. Individual noise immission was then calculated while disregarding any other acoustical influence. This is justified with respect to the primary goal of the study, to estimate the difference between road and rail traffic noise with regard to physiological, subjective, and behavioral responses, but does not meet the real situation. As shown in [Figure 3] measured indoor noise levels (on the ordinate) differ considerably from calculated source-specific noises (on the abscissa), probably due to various other outdoor noises and additional indoor noises as produced by air conditioning and other electrical devices, by family members, neighbors, and animals which are more significant and thereby more disturbing than external noises.
Sleep timing: The distribution of the times for going to bed, getting up, falling asleep and final awakening [Figure 4] reveals that half of the participants get up after the end of the legally defined night (10 pm to 6 am). On the one hand, sleep becomes flatter the more it is shifted forward, on the other hand road traffic noise and indoor noise increase after 6 am. Though noises emitted from railway traffic are almost evenly distributed over the 24 hours of the day, the increase of road noise in the early morning concerns residents at railway tracks as well as rail noise is almost ever combined with road noise and as the influence of both these noises cannot be clearly separated during the day.
These situations are expected to become more frequent in the forthcoming years as on the one hand traffic densities increase and as on the other hand the variability of sleep times will increase concomitantly due to increasing flexibility of working hours, i.e. an increasing number of persons are expected to go to bed and/or to get up outside the legally defined night (10 pm - 6 am). So, new concepts are needed for the protection of sleep.
Most of the data recorded during the sleep observation period did not reveal any dependency to the noise level. This was true for the data recorded during sleep, i.e. body movements, the subjective evaluation of the qualitative and the quantitative parameters of sleep and for qualitative and quantitative test performance. As the Null-hypothesis was not rejected in this study, the results neither support nor refute the advantage for rail noise that is currently applied in Germany. The fact that the persons exposed to rail noise slept significantly more often with open windows than the residents exposed to road traffic again rather supports the existence of a difference in favour of rail noise but this effect cannot be unequivocally related to noise. However, on the basis of these data it is impossible to quantify that difference in terms of equivalent sound pressure levels. Regarding future research it might be advantageous to select more homogenous participants exposed to clearly different sound pressure levels and to introduce an 'experimental phase' i.e. where the sound pressure levels during several interspersed nights are reduced or enhanced.
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