Methods for identifying quiet areas

·       Noise maps provide an easily interpreted visual presentation of the distribution of calculated sound-pressure levels from given noise sources, such as traffic or industry, in a given region, and for a defined period.

·       Calculation of sound-pressure levels are more cost-efficient than actual measurements, particularly if a large area is to be mapped, because it is necessary to have many measurement or receiver points.

·       Noise maps present calculated sound-pressure levels from environmental noise, separated from other sources. Please observe that the definitions of ‘quiet area’ in the END presuppose that this distinction is possible in practice.

·       Noise maps are particularly useful when planning a new area. At the planning stage actual measurements are not possible, because the noise sources, like roads and vehicles, do not yet exist in the area.

 Limitations

·       Noise maps are based on mathematical models of how environmental noise propagates outdoors under given and restricted conditions. Deviations from the given criteria results in calculated sound-pressure levels that do not correspond to reality. Examples of factors that may influence the results are topography, architecture, weather, as well as façade and surface material. Noise maps must be validated by actual measurements.

·       Noise maps are typically based on one noise source at a time (road traffic, railway traffic, aircraft, or industry). It is important to calculate the net effect of sound-pressure levels from multiple and simultaneous noise sources, else the sound-pressure levels may be underestimated.

·       Noise maps do not include positive sounds, like wind in trees, purling water or birdsong.

·       Noise maps identify quiet areas based on calculated sound-pressure levels. One must keep in mind that an area which is undisturbed by environmental nose, for example a marsh land, may not necessarily be valuable to human health, when considering other aspects than environmental noise.

·       Noise maps typically present calculated A-weighted sound-pressure levels. These values do not provide an accurate representation of how people perceive the acoustic environment, not even with regards to loudness (e.g., Nilsson, 2007a, 2007b). Sound provides a lot more information to human beings than magnitude.

The COST members have in the last several years developed techniques and concepts to produce alternative maps (see web of the soundscape COST Action: http://www.soundscape-cost.org/, as well as relevant publications by the COST members), including

·         sound maps, which include both noise (e.g. traffic noise) and positive sounds

·         psychoacoustical maps, where psychoacoustical parameters like sharpness etc can be mapped

·         soundscape maps based on the previously surveyed soundscape evaluation, using artificial neural network techniques (Yu and Kang, 2009).

 
8.2 Measurement of sound-pressure levels

Besides calculating the sound-pressure levels, many authorities measure the actual levels in situ. These measurements are typically used to complement or to validate the noise maps.

 
Benefits

·       Measurements provide the actual sound-pressure levels at a given place at a given time, and may better reflect reality than models and calculations. Under conditions for which calculation models do not apply, this is the only method to obtain accurate sound-pressure-level data. For a long time the calculation models could not accurately predict the sound-pressure levels in court yards enclosed by buildings. As noise mapping evolves, new similar limitations will likely be discovered.

 Limitations

·       To measure sound-pressure levels is time consuming, labour intensive and costly, particularly if a large area is to be mapped, using many measurement points.

·       Presently, measurements cannot distinguish sound-pressure levels from different sources, and measure environmental noise separately. This is particularly important to quiet areas. The actual measurement is a mixture of sound-pressure levels from various sources, including the sounds of the place – such as sounds of people, wind in vegetation and flowing water – and environmental noise. This means that there is a risk of a mismatch between calculated and actual sound-pressure levels, and that measurements cannot be used to validate the calculated levels of environmental noise in a quiet area. Please observe that the definitions of ‘quiet area’ in the END presuppose that it is possible to distinguish environmental noise from other sources.

·       Measurements are typically based on A-weighted sound-pressure levels. These values do not provide an accurate representation of how people perceive the acoustic environment, not even with regards to loudness (e.g., Nilsson, 2007a, 2007b). Sound provides a lot more information to human beings than magnitude.

 Techniques and basic concepts have also been developed by COST members on the automatic identification of sound types, using data of real-time measurement in situ, or recording. This could be linked to sensor city project, with a gird of microphones across an area. By identifying the type of sounds, with measured sound levels, the evaluation of quiet areas can be better made. (see web of the soundscape COST Action: http://www.soundscape-cost.org/, as well as relevant publications by the COST members, also Yang and Kang, to be published in the soundscape special issue of JASA).

 8.3 Evaluation of user/visitor experiences

The purpose of preserving quiet areas is to protect human health. This includes protecting people from noise annoyance and sleep disturbance, which are psychological factors that cannot be measured with physical measuring instruments. Thus, it is essential to know how people perceive quiet areas. This insight in combination with the limitations of calculated and measured sound-pressure levels, particularly with regards to quiet areas, have fuelled the interest in soundscape studies. The launch of the European Soundscape Award, sponsored by the European Environment Agency, underlines the progress and importance of the soundscape approach in Europe.

 Benefits

·       Only evaluation of user/visitor experiences can provide insight into how people perceive a quiet area. Such studies may include, but are not limited to, perception of how dominant different sound sources are, perceived acoustic quality or appreciation, tranquillity, annoyance, what sounds are appropriate to the place, recreational value and actual use of the area.

·       In contrast to present sound-level meters, human beings can distinguish the intensity of sounds from different sources, like technology, humans and nature. Such measurements have repeatedly been proven to be a stronger predictor of perceived acoustic quality in an area than A-weighted sound-pressure levels (e.g., Nilsson, 2007a, 2007b).

·       Perceived acoustic quality is not limited to the acoustic environment per se, but also influenced by the visual quality of an area. A lush and green environment may increase perceived acoustic quality and reduce annoyance, even though greenery has a limited influence on sound-pressure levels. Physical measuring instruments cannot capture such psychological effects.

 Limitations

·       Evaluation of user/visitor experiences is typically conducted by questionnaire surveys in situ. This method is weather dependent in that it is hard to conduct surveys when the weather is bad (rain, wind, cold). On the other hand, people are reluctant to visit quiet areas during bad weather conditions, and there is no point in conduction user/visitor surveys when there are no visitors.

·       Like measurements of sound-pressure levels, evaluation of user/visitor experiences is time consuming, labour intensive and costly. They require time for preparation and to develop appropriate questionnaires. Typically they require a relatively large staff, and time to collect the questionnaires. They also depend on the visitors’ willingness to participate in the survey. After data collection, the date must be processed, which requires both time and skill.

·       Evaluation of user/visitor experiences requires expertise in behavioural science in order to develop appropriate questionnaires. The quality of the data depends on the developer’s skills and experience in the field, particularly soundscape and environmental psychology.

·       As of yet, there are no standardised methods for evaluation of user/visitor experiences of quiet areas. Such standards, like a standardised questionnaire, would make this method more available to non-experts.

 ISO Working Group 54 is currently working on minimum criteria for soundscape research and reporting. And the Working Group 2 of the COST Action has compared various survey methods and also identified some issues to be evaluated.

 8.4 Expert assessments

As stated above, identification of quiet areas by sound-pressure levels is limited in that an area which is undisturbed by environmental noise may not necessarily be valuable to human health, when considering other aspects than environmental noise. For this reason it is important to include other criteria, besides sound-pressure levels. Such criteria may include land-use plans, cultural heritage, ecological values, social and recreational values, and accessibility. Assessment of such criteria typically requires expertise.

 Benefits

·       Expert assessments of a potential quiet area contribute with valuable insights on other aspects of the area than sound-pressure levels. Experts may include urban planners, landscape architects, sociologists, biologists, psychologists, and antiquarians, as well as acousticians.

·       Involving experts, who contribute with different points of views early in the process, helps to achieve an appropriate outcome faster, than if only a limited set of criteria, like sound-pressure-level data from noise mapping, is considered.

 Limitations

·       Skilled experts are in short supply.

·       Like sound-pressure-level data, expert assessments do not provide information on how users/visitors experience a quiet area.