The ability to hear sounds is a sensory function vital for human survival and communication. However, not all sounds are wanted. 'Unwanted sounds', for which the term 'noise' is normally used, often have their origin in human activities (mainly transport, industry and households).
This article addresses environmental noise also referred to in the scientific literature as community, or residential, noise. Environmental noise is the noise experienced by people generated outside households. Noise experienced by people in the workplace or occupational environment is not considered in this study.
The current article first concentrates on the concepts involved with the measurement of noise and vibration. This is followed by an assessment of the effects of noise on human health and nature, and then by a review of noise sources in Europe.
The availability and comparability of data on noise pollution in Europe are generally poor (Box A). Available data published by the OECD show that exposure to noise, which was fairly stable at the beginning of the 1980s, had increased by the end of the decade in some Western European countries (eg, France, Germany, The Netherlands, Switzerland) (OECD, 1991a). For sound levels Leq greater than 65 dB(A) (see Box B for a definition of Leq), exposure appears to have stabilised in some cases and increased in others. However, within the range 55 to 65 dB(A), exposure has significantly increased, apparently as a result of the fast-growing volume of road traffic . In the highly industrialised European countries such as Belgium, France, Germany, Italy, The Netherlands and the UK, but also Austria, the Slovak Republic, Spain and Switzerland, more than 50 per cent of the population is exposed to noise levels from road transport which are above Leq 55 dB(A), which is the level at which people become seriously annoyed during the daytime (WHO, 1993a).
Box A. The state of information on noise
An inventory published in 1993 from 14 European countries of the people exposed to noise levels due to road, rail and air traffic, ranging from 55 dB(A) to above 75 dB(A) (in terms of Leq from 06.00 to 22.00) has been compiled by OECD (OECD, 1993). Although not all European countries are included, this is the most comprehensive survey of this kind, and the results are used in this report, combined with some additions from other sources (Umweltbundesamt, 1989, 1992a; UK DoE, 1992; WHO, in press). For exposure data due to noise from industry, use has been made of WHO data (WHO, in press) and of German data (Umweltbundesamt, 1989). The OECD has also published time-series data for ten European countries of the population exposed to various noise levels around airports expressed in daytime Leq dB(A) (OECD, 1993).
Also featured in this report is a survey of 18 European cities with data on the percentage of population exposed to outdoor noise greater than Leq 65 dB(A) and 70 dB(A).
The conspicuous paucity of data from most of the Central and Eastern European countries appears to be a serious shortcoming. Quantitative statements from these countries are very scarce and rudimentary; however, the various reports on the state of the environment, prepared, for example, for UNCED in Rio in 1992, mention noise as an environmental problem of growing concern in the light of the incipient, rapid growth of road traffic and the expected development of industry.
It should be noted that data on noise from the different countries are often not obtained by the same method or using the same descriptors. In general, models have been used which are based on noise measurements and acoustical calculations on a limited number of typical locations. The results are then extrapolated to the whole country. The accuracy and representability of such models vary from country to country and some of them appear rather simplified. The designation of specific source categories for noise also varies (eg, transport, industry, tourism, etc). For these reasons statistics from different countries should be compared with caution.
Box B. Measurement of noise
There are two main ways of assessing the influence of noise: by physically measuring sound pressure levels, and by recording the discomfort or annoyance caused by noise. Physically noise is treated as an acoustic phenomenon called sound. A sound event as a physical phenomenon can be fully described by four parameters:
the strength or sound pressure, mostly expressed in terms of the amplitude of the sound pressure waves, and is usually measured as sound pressure levels in decibels (dB);
the frequency or pitch, measured in Hertz (most noises consist of a mixture of sounds with various pitches and frequencies, and hence do not have a recognisable pitch in any musical sense);
the fluctuation of sound with time (also known as the time history), measured as sound pressure level as a fluctuation of time;
sound character, which describes the particular features of a sound (eg, tonal and harmonic qualities).
Decibels are measured on a logarithmic scale, so that an increase of the sound pressure level (SPL) by a factor of 10 would result in a 10 dB increase in sound level, an increase of SPL by a factor of 100 would result in a 20 dB sound level increase, a factor of 1000 would result in a 30 dB increase, and so on. The decibel scale ranges from 0 (the threshold of normal human audibility) to 130 (the threshold of pain). For most purposes the frequency scale is weighted by the frequency sensitivities of the human ear, known as A-weighting, transforming the (unweighted) sound pressure (dB) into A weighting sound pressure level ('dB(A)'). The dB(A) scale strongly attenuates the low frequencies and moderately attenuates the very high frequencies. The way in which the dB(A) scale corresponds to everyday noises is shown in Figure 1, where it can seen that the range of everyday noises varies from roughly 45 dB(A) to 115 dB(A).
The main descriptors used in the assessment of environmental noise are shown in Table 1. For describing the impact of noise on humans, the so-called Equivalent Sound Pressure Level (Leq) needs to be calculated, that is, the mean value of sound intensity over time expressed in decibels. The significance of the Leq is to be seen in the hypothesis that a noise that varies through time is equivalent in its disturbance on humans to a steady constant source of noise, over the same interval of time, if the noise level (sound pressure level) of the constant source of noise is equal to the Leq value of the noise that varies through time. However, Leq is not enough for the characterisation of environmental noise. It is equally important to measure and display the maximum values of the noise fluctuations (Lmax), preferably combined with a measure of the number of noise events (Ln) (WHO, 1993a). For most people, noise pulses are more annoying than a steady pulse of noise.
Apart from the descriptors listed in Table 1, there are a number of other descriptors used in European countries, notably with regard to aircraft noise (eg, in the UK, The Netherlands and Norway). The use of such a variety of descriptors makes international comparisons of noise exposure difficult, if not impossible. However, as far as can be judged from the serious efforts being made by the scientific community, through various international bodies, such as the International Organization for Standardisation (ISO) and the European Committee for Standardisation (CEN), it appears there is a preference towards those descriptors based around the concept of Leq.
The actual annoyance to people caused by noise is normally measured by sociological investigations, in the laboratory, or by analysing complaints by type of noise source to local authorities. Such figures should, however, be treated with caution, as people tend to be disturbed by, and react differently to, different types of noise. It is possible to relate annoyance to noise measured in terms of Leq to obtain 'dose-effect curves'. These have assumed a prominent role in quantifying the impact of environmental noise on people. The general conclusion from dose-effect curves is that people are becoming 'considerably annoyed' if environmental noise levels are in excess of about 40 dB(A) at night and 50 dB(A) during the day.
The effects of noise
The nuisance effects of noise are difficult to quantify, as people's tolerance to noise levels and different types of noise vary considerably. Distinct variations in noise intensity and noise levels can occur from place to place (even within the same general area), and from one moment to the next. Similarly there can be large variations during each day, week or year. The main effects on people from noise occur along roads in both cities and rural areas, around airports and in residential areas.
The impact of noise on sensitive groups deserves particular attention (eg, school children, the elderly, the sick). The reaction of these groups may be considered as warning signals as to what may happen to other groups on exposure at higher noise levels. This group could constitute as much as 30 per cent of the population (K Andersson, Swedish Environmental Protection Agency, personal communication, 1994).
This is perhaps the most common adverse effect of noise on people and many complaints are made every year about many different types of noise. The feeling of annoyance results not only from interference with communication and sleep disturbance, but also from less well-defined feelings of being disturbed and affected during all kinds of activities as well as during periods of rest. There is, for example, evidence of a clear relationship between degrees of individual annoyance and noise levels; for example, it has been demonstrated that less use is made of private gardens and public parks when there is too much noise (OECD, 1991b).
If the percentage of the population which feels 'considerably annoyed' by the noise is determined through sociological surveys, then a picture like that in Figure 2 emerges. It shows how the various classes of noise sources, namely road traffic, air traffic, rail traffic and industry, contribute significantly to annoyance.
Whether and to what extent such exposure is ultimately harmful to human health and well-being has not yet been fully and conclusively explored, except at very high sound levels, when it causes hearing loss and tinnitus (ringing in the ears). The present state of knowledge, however, clearly indicates that long-term health effects due to environmental noise exposure cannot be excluded. In addition, a number of well-defined harmful effects on the quality of sleep, communication and psycho-physiological behaviour can be identified. There is a lack of evidence to indicate that such reactions to noise diminish with time, although within certain limits tolerances may be built up. However, it seems that complete physiological habituation to sleep-disturbing noise does not occur, not even after several years of exposure (Suter, 1992, in WHO, in press).
Sleep disturbance is probably the most apparent effect of environmental noise. It can also be interpreted as a reduced quality of sleep, and may even occur when the people affected are not aware of it (H Ising, BGA, Berlin, personal communication). To ensure undisturbed sleep, single noise events (such as a passing aeroplane) should not exceed a maximum sound pressure level of approximately 55 dB(A) (H M Müller, DG XI, CEC, personal communication).
Interference with communication
The degree of interference of noise with speech or music depends on the noise level in relation to the level that conveys the desired information. An increasing noise level requires speakers to raise their voice and/or to get closer to the listener in order to be understood. Noise levels from about 35 dB(A) and above are seen to interfere with speech communication until, at noise levels of about 70 dB(A), normal speech communication becomes virtually impossible (Verein Deutscher Ingenieure, 1988, in von Meier, 1993). In classrooms where teaching has to take place over long distances, noise levels should not exceed 25 dB(A) (K Andersson, Solna, personal communication).
A great number of psycho-physiological effects of noise have been reported in the literature (WHO, 1993a). The most common responses are physiological stress, and at higher noise levels, cardiovascular reactions. Mental health effects and influences on performance and productivity have also been observed and documented (von Meier, 1993).
Intensive research on these subjects is ongoing (eg, Miedema, 1993), but it can be generally concluded from the present state of knowledge that exposure to environmental noise acts as a stressor to health, as it leads to measurable changes in, for example, blood pressure and heart rate. But there is not sufficient evidence yet to relate the exposure to environmental noise levels directly to specific health effects, although such relationships can by no means be excluded. It is presumably the total load of stressors, of which environmental noise is only one, that has a harmful and lasting effect on physical and mental health, seen as a statistical entity that allows great individual variations (see WHO, in press, for more details).
Low frequency noise and vibrations
While noise is pressure variations in air, vibration is wave motion in solid bodies, normally of low frequency. Low frequency noise and vibration are hence closely related. Vibrations will intensify the noise annoyance. Both have been linked with causing disturbance in residential areas. Vibration has not been well analysed.
The effects of noise on wildlife
The effects of noise on the natural environment have not yet been fully explored. Research results available point to extra-auditory effects, mainly unspecific stress reactions, on animals with an acute sense of hearing, under extremely high noise exposures from low-flying aircraft (Umweltbundesamt, 1987). However, noise effects of major proportions or of lasting harmful consequences on nature have not been reported. The evidence available so far is too sketchy and inconclusive fully to exclude such effects.
Environmental noise also has implications for costs and benefits in the economy more generally. For example, cost effects are known to exist as a result of the general degradation of residential areas by exposure to environmental noise (eg, lowering of rents and property prices). Noise-induced illnesses, losses of productivity, and a higher rate of accidents caused by sleep disturbance have obvious cost effects, but these are extremely difficult to quantify. There are recent indications that certain producers of low-noise equipment may gain some economic advantage over their competitors as public awareness of environmental noise disturbances increases.