Traffic noise is the most important source of environmental annoyance. According to the Environmental Expert Council of Germany, severe annoyance persistent over prolonged periods of time is to be regarded as causing distress. Previously, extraaural noise effects were mostly assessed using a paradigm in which the sound level played the major role. On the basis of this paradigm the relatively low sound level of environmental noise was not considered to be a potential danger to health. In contrast to this numerous empirical results have shown long­term noise-induced health risks. Therefore a radical change of attitude - a change of paradigm - is necessary. For an immediate triggering of protective reactions (fight/flight or defeat reactions) the information conveyed by noise is very often more relevant than the sound level. It was shown recently that the first and fastest signal detection is mediated by a subcortical area - the amygdala. For this reason even during sleep the noise from aeroplanes or heavy goods vehicles may be categorised as danger signals and induce the release of stress hormones. In accordance with the noise stress hypothesis chronic stress hormone dysregulations as well as increases of established endogenous risk factors of ischaemic heart diseases have been observed under long-term environmental noise exposure. Therefore, an increased risk of myocardial infarction is to be expected. The results of individual studies on this subject in most cases do not reach statistical significance. However, according to the Environmental Expert Council, these studies show a consistent trend towards an increased cardiovascular risk if the daytime immission level exceeds 65 dB(A). Most of the previous studies on the extraaural effects of occupational noise have been invalidated by exposure misclassifications. In future studies on health effects of noise a correct exposure assessment is one of the most important preconditions.

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Mainly dependent on level and dynamic increase sound produces over-shooting excitations which activate subcortical processing centers (e.g. the amygdala, functioning as fear conditioning center) besides cortical areas (e. g. arousing annoyance, awakenings) as well. In addition there exist very close central nervous connections between subcortical parts of the auditory system (e.g. amygdala) showing typical plasticity effects (sensitization) and the hypothalmic-pituitary-adrenal (HPA)-axis. Using that causal chain noise induce cortisol excretion even below the awakening threshold. Thus repeated noise events (e.g. overflights during night time) may lead to accumulation of the cortisol level in blood. This can happen because its time-constant of exponential decrease is about 50 to 10 times larger than that one for adrenaline and noradrenaline. This fact and the unusual large permeability of cortisol through the cell membranes opens a wide field of connections between stress-dependent cortisol production and the disturbance of a large number of other endocrine processes, especially as a result of long-term stress activation by environmental influences such as environmental noise. Based upon a physiological model calculating the cortisol accumulation starting at a nightly threshold of physiological over-proportional reactions around L _max =53 dB(A) the number of tolerable noise events (over-flights in a nightly time range) can be estimated for given indoor peak sound pressure levels, keeping the cortisol increase within the normal range. Examples of results for 8 hours in the night are for instance number and level combinations (NAL-values) of 13 events with 53 dB(A) indoor peak level or 6 events with 70 dB(A) indoor peak level repectively.

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In noise effect research often the awakening reaction is maintained to be the only important health related reaction. The main argument is that sleep represents a trophotropic phase ("energy storing"). In contrast to this awakening reactions or lying awake belong to the ergotropic phase ("energy consuming"). Frequent or long awakening reactions endanger therefore the necessary recovery in sleep and, in the long-run, health. Findings derived from arousal and stress hormone research make possible a new access to the noise induced nightly health risk. An arousal is a short change in sleeping condition, raising the organism from a lower level of excitation to a higher one. Arousals have the function to prevent life-threatening influences or events through activation of compensation mechanisms. Frequent occurrences of arousal triggered by nocturnal noise leads to a deformation of the circadian rhythm. Additionally, the deep sleep phases in the first part of the night are normally associated with a minimum of cortisol and a maximum of growth hormone concentrations. These circadian rhythms of sleep and neuroendocrine regulation are necessary for the physical as well as for the psychic recovery of the sleeper. Noise exposure during sleep which causes frequent arousal leads to decreased performance capacity, drowsiness and tiredness during the day. Long-term disturbances of the described circadian rhythms have a deteriorating effect on health, even when noise induced awakenings are avoided.

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World wide rules for sleep staging originate to 1967. Since then many investigations aimed to give numbers for the degree of sleep disturbances due to air traffic noise. But the variables used, such as the amount of relative sleep stages, total sleep time, or sleep efficiency, could not explain impairment in health and performance sufficiently. The beginning of the eighties has given new insight into the restorative functions of sleep, according to sleep fragmentation by micro-arousals. These are originating in autonomous dysfunctions during sleep, leading to non-restorative sleep. Environmentally related sleep disturbances are described, EEG and vegetative (micro)-arousals, and the actual knowledge in sleep medicine is given in terms of the international classification of sleep disorders (ICSD). The effects on health, and disturbed performance capacity during the day are shown by self ratings of 160 patients. Elevated metabolic rate caused by micro-arousal and/or insomnia, may play an additional role in health impairment.

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Due to the undisputable restorative function of sleep, noise-induced sleep disturbances are regarded as the most deleterious effects of noise. They comprise alterations during bedtimes such as awakenings, sleep stage changes, body movements and after-effects such as subjectively felt decrease of sleep quality, impairment of mood and performance. The extents of these reactions depend on the information content of noise, on its acoustical parameters and are modified by individual influences and by situational conditions. Intermittent noise, that is produced by air traffic, rail traffic and by road traffic during the night is particularly disturbing and needs to be reduced. Suitable limits are suggested.

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The WHO definition of "health" is critically discussed in its broad context. Decision making in noise policy has to be made in the evaluation range between social and physical well-being. The term "adverse" is a crucial one in the process of risk characterization. In toxicological terms it refers to the single event itself; in psychosocial terms it refers to the relative number of people affected. The evidence of the association between community noise and cardiovascular outcomes is evaluated. The results of epidemiological studies in this field can be used for decision making when assessing maximum acceptable noise levels in the community. Since dose response relationships were mostly studied with respect to road traffic noise, inferences have to be made with respect to aircraft noise. Issues of statistical inferring are discussed.

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Noise protection associated with the construction and extension of airports in the Federal Republic of Germany has been regulated by the law for protection against aircraft noise since 1971. This legislation is due for revision because of different aspects. One aspect is the growth of air traffic which has led many airports to the limits of their capacity and in search of new ways of adaptation to the increasing demand for flight services. Another aspect is the increasing concern of the population about noise effects which has to be addressed by better protection against the effects of aircraft noise. The framework conditions of policy in terms of society as a whole, its health and economic environment need to be put into effect by political action. Science can contribute to this goal by performing noise effects research and by providing recommendations to the political body. However, it remains controversial, what measures are necessary or adequate to assure effective protection of the population against aircraft noise. This is particularly true for the protection of rest and sleep at night. The problem of finding a common basis for adequate recommendations is associated with (1) the low number of primary studies, which also exhibited highly variable results and assessments, (2) the handling of acoustic or psycho-acoustic dimensions for quantifying psychological or physiological reactions, and (3) the conception of how far preventive measures have to go to prove effective. With this in mind, the DLR Institute for Aerospace Medicine is conducting a large-scale, multi-stage study for investigating the acute effects of nocturnal aircraft noise on human sleep. This enterprise is implemented in the framework of the HGF/DLR project "Quiet Air Traffic" for developing sustainable assessment criteria for human-specific effects of aircraft noise at night.

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When planning the development or reduction of large traffic facilities, acoustic calculation procedures are used to forecast the noise load in the affected residential areas. Then, existing dose/response relationships for steady state situations are used to predict noise effects in future years. Planners often assume that (1) noise annoyance reactions of residents do not change over the years, and (2) annoyance is not affected by the change itself. Both of these assumptions are questioned in this paper, and a procedure for estimating future annoyance in changed noise situations is proposed. This includes the analysis of possible statistical trends of the annoyance reactions over the years - even for steady-state noise loads, and with changing state situations, the effects of the change should also be accounted for

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Summary. Disturbing effects of aircraft noise depend on the time of day at which the sound sources emerge. The reason can be seen in different human activities which vary qualitatively throughout the day. Especially in the evening and during the night people are more sensitive against noise induced disturbances which is a result of several field studies. Additionally there exists empirical evidence that human performance behaviour profits by keeping the night period free of sound exposure. As a consequence of these findings it is discussed whether the existing air traffic should be rescheduled to the daytime. It is argued that not only noise rescheduling needs to be considered, but also the spatial redistribution of air traffic volume. In using a mix of rescheduling techniques and administrative possibilities, significant reductions of aircraft noise exposure can be achieved.

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The "Special Assessment of Environment and Health" (SAEH) by the Council of Experts for Environmental Questions of Federal Republic of Germany is presented regarding to it's statements concerning the consequences of aircraft noise during night. Considering the issue of sustainability it is emphasized that lower limit values of the validity of scientific results need to be accepted. As the discussion of the literature shows the statements of the Council are rather vague and warily. This is a question of used parameters of noise effects during the night as well as its interpretation. It seems necessary to utilize a hierarchical structure of limit values and with interpretation of the term "threshold" as normal physiological reactions. More investigations are necessary in this field.

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