Executive summary
In this report, the 'Uniform environmental noise exposure metric' Committee of the Health Council of the Netherlands proposes a system of environmental noise exposure metrics for risk assessment of and policy decision-making on the adverse effects of environmental noise on the health and well-being of residential communities.
Request for advice and background
The Minister of Health, Welfare and Sport and the Minister of Housing, Spatial Planning and the Environment requested the Health Council to recommend a system of environmental noise exposure metrics. This system should be simple, transparent, in agreement with binding international regulations, and applicable to all environmental noise sources outside the home. The request is to be viewed against the background of the present use of a variety of source-dependent noise metrics associated in different ways with noise-induced health effects.
The present report, which answers the Ministers' request, is part of the national policy project MIG: Modernisering Instrumentarium Geluidbeheer (Modernization of Policy Tools for Noise Management). This project should result in a policy revision that aims at simplifying the environmental noise regulations by introducing more transparency, flexibility and delegation to provincial and municipal authorities.
Specification of adverse effects
The request for advice was limited to exposure to environmental noise. The former Health Council Committee on Noise and Health showed in its report that noiseinduced general annoyance and sleep disturbance are the most widespread effects of environmental noise on the population of the Netherlands. The system of noise metrics is developed in such a way as to be able to assess these effects within communities in residential areas independent of the type of noise source. This is done by adjusting physical noise exposure metrics, using exposure-response relationships based on empirical data, in such a way that source-dependent differences in the exposure-response
relationships disappear.
In surveys it is common practice to specify the degree of general annoyance in a population by the 'percentage of the population that is highly annoyed' (%HA). A subject is considered to be highly annoyed if he (or she) rates his (or her) degree of general annoyance on a scale from 0 to 100 with a score of 72 or over. ('Not at all annoyed' is at the lower end of the scale and 'extremely annoyed' at the upper end.) This measure of general annoyance is also used in this report.
Sleep disturbance is specified here by two measures of effect, one for sleep disturbance annoyance and another for awakening. Similarly to general annoyance, sleep-disturbance general annoyance is assessed by the percentage of people highly annoyed by noise-induced sleep disturbance (%HS). Awakening is specified, only for situations involving isolated noise events during sleeping time, by a count of the number of noise-induced awakenings in an adult person.
Basic concept of the system
The Committee proposes a system of two metrics to quantify long-term environmental noise exposure in communities:
a EEL : environmental exposure level, associated with general annoyance due to
long-term exposure to environmental noise during the 24-hour daily cycle
a ENEL: environmental night-time exposure level, associated with sleep disturbance
(annoyance and awakenings) due to long-term night-time exposure to environmental noise.
These metrics are specified in such a way that, irrespective of the type of noise source, situations in residential areas with the same EEL lead to approximately the same level of general annoyance in a community. Similarly, in situations with the same ENEL,
communities would experience approximately the same level of noise-induced sleep
disturbance.
The available data are insufficient to complete the full specification of EEL and ENEL. Therefore the Committee starts the uniforming process with the introduction of the noise metrics L,adjusted,den and Ldj.,,,d.23-07h' These metrics are explained below. The Committee indicates the actions that should be undertaken to specify the system completely.
Determination of EEL
The determination of the EEL for a specific environmental noise source starts by expressing exposure to noise from that source during a part of the day by means of the equivalent sound level during that period. Then differences in general annoyance which depend on special characteristics of the noise (e.g. tonal and impulsive components, the period of the 24-hour daily cycle in which the noise occurs and the type of noise source) are taken into account.
In the first step for determining the EEL, adjustments are applied to the equivalent
sound level to account for special noise characteristics. These adjustments are appropriate in the following situations:
non-impulsive continuous industrial noise: adjustments are tentatively proposed for application which vary from 0 to 10 dB(A)
situations with audible tones in the noise: adjustments are tentatively proposed for application which vary from 0 to 5 dB(A)
situations with (highly) impulsive components: adjustments are 5 or 12 dB(A).
Adjustments for tones and impulses are generally not deemed necessary for situations involving common modes of present-day transport. The Committee recommends that the need for adjustments for tonal or impulsive components be the subject of a study for new modes of transport.
In the next step, the three (adjusted) equivalent sound levels over the three periods of the 24-hour daily cycle (day-time: 07.00 - 19.00 hours ; evening-time: 19.00 - 23.00 hours; night-time: 23.00 - 07.00 hours) are determined and adjusted with respect to the time of occurrence of the noise,, by adding 5 dB(A) to the adjusted equivalent sound level during the evening and 10 dB(A) to the adjusted equivalent sound level during the night. In addition to this, an exponential average of the three adjusted equivalent sound levels is calculated to determine a value representative for the full 24-hour pe-
riod (Ldj.,,,dd,,).
The final step in the derivation of EEL, the uniform environmental noise exposure metric related to general annoyance, would be to adjust the adjusted equivalent sound level for the 24-hour daily cycle in such a way that the exposure-response relationships for aircraft and rail (train and tram) traffic noise coincide with those for road traffic noise and stationary noise sources, such as industries, shooting ranges and shunting yards. However, the Committee stops short of making this final step, the main reason being that agreement must be reached on the most appropriate measure of effect. Although %HA is widely used, other measures are prescribed in some regulations. As the decision on this matter is largely of a political nature, the Committee presents its derivation of the EEL as an example.
Determination of ENEL
To determine the ENEL, the noise exposure from 23.00 to 07.00 hours is considered. As specified for the determination cf the EEL, the equivalent sound level is adjusted to account for special noise characteristics to obtain Ldj.,,.d.23-07h'Then adjustments that take into account the type of noise source should be applied. The Committee is not able to make this final step, since the exposure-response relationships for the various noise sources require further evaluation before they can be taken as sufficiently stable for specifying ENEL. The report presents preliminary exposure-response relationships for sleep-disturbance annoyance for situations involving transport noise and noise from stationary sources, and a preliminary relationship for the maximal number of noiseinduced awakenings in adult persons which is limited to situations with isolated noise events during sleeping time. From these relationships an indication of the adjustments required is obtained.
Discussion of the proposed system
The Committee is of the opinion that, to a large extent at least, the system meets the requirements put forward in the request for advice.
Transparency The system has a high degree of transparency. Using the two proposed metrics EEL and ENEL, in many relevant situations of environmental noise exposure the expected general annoyance and sleep disturbance can be estimated from simple relationships, irrespective of the noise source. Also, the system with and Ladjusted.23-07h is much more transparent that the present Dutch system.
International agreements The proposed system is to a large extent in accordance with the authoritative ISO document 1996-2 on the description and measurement of environmental noise pertinent to land use. The system is also in line with the conclusionsof the international conference on future EU noise policy, held in May 1997 in the Netherlands (The Hague).
Simplicity of assessment and measurement The proposed noise metrics are based on the equivalent sound levels during specific parts of the 24-hour daily cycle. These equivalent sound levels can in principle be easily used in noise emission and immission calculation models and measured with simple, relatively inexpensive acoustical equipment. The Committee recognizes that measuring environmental noise in practical situations is complicated due to e.g. (noise from) intervening human activities, variations in noise situations from day to day and requirements for noise-source specific measurement results. In most instances, the determination of special characteristics of noise requires advanced acoustical instrumentation. However, a proper assessment of t@.ese special characteristics, which is relevant in only a minority of cases, is necessary and unavoidable to prevent underestimation of the levels of general annoyance and sleep disturbance.
The noise metrics have been specified as values representative for a year. It is common practice to determine noise exposure for national, regional or local purposes either by using calculation methods or by extrapolating the results of (representative) samples of measurement results. In both instances this requires specific expertise which is sometimes beyond the knowledge of the users of the system. However, any other system of metrics for the reliable estimation of noise-induced adverse effects would also require such expertise.
Applicability It is expected that the system will be applicable to the lar,,e majority of situations involving environmental noise exposures, such as situations with exposure to noise from road, rail and aircraft traffic and from industries, shunting yards and shooting ranges. It is important to note that the system of metrics is designed to assess health effects due to long tenn environmental noise exposure, and not to assess health effects shortly after the noise levels show a sudden change, e.g. due to noise reduction measures in the neigbourhood or the use of a new railway line.
Exposure to infrequently occurring noise from, for example, the occasional passage of a helicopter (for rescue purposes), ultra-light aircraft and small aircraft (for advertising purposes), or pop concerts and sporting events cannot be assessed using the proposed metrics. The Committee recommends further research on this subject.
The Committee recognizes that noise from neighbouring dwellings and from activities in the near vicinity is an important cause of general annoyance. However, nonacoustical factors play a role in people's appraisal of such noises to a larger extent than in the case of traffic noise. Therefore it is considered unlikely that the proposed system, even with amendments, will be able to predict general annoyance in these situations. Further psycho-acoustical surveys may be able to reveal important acoustical, psychological and social variables in this respect.
it has been found that people's reactions to low-frequency noise, once they perceive this type of noise in their living environment, are usually so severe as to suggest that appropriate adjustments may be in the order of 40 dB(A). The Committee recommends further investigation on this subject before applying the proposed system of metrics (with incorporation of the appropriate adjustments) in such situations.
The Committee is of the opinion that inclusion of a detailed recommendation for rating high-energy impulsive noises such as sonic booms, was beyond the scope of the present report.
The Committee discussed the possibility of using the proposed system of metrics for assessing the combined effect of two or more different noise sources, each producing similar general annoyance or sleep disturbance. As yet, there is no generally accepted method to assess this effect. Also taking into account the limited available time, the committee considered it not possible to formulate a proposal for this complicated subject at this moment.