Norwegian authorities have developed and adopted a method for assessing the magnitude of noise impact on a community in quantitative terms. The method takes into account all levels of noise annoyance experienced by all the residents in an area and transforms these data into a single quantity that can also be expressed in monetary terms. This method is contrary to other commonly used assessment methods where only a certain fraction of the impacted people, e.g. those "highly annoyed," is considered.
Keywords: Noise, annoyance, economic impact
|How to cite this article:|
Gjestland T. The socio-economic impact of noise: A method for assessing noise annoyance. Noise Health 2007;9:42-4
| Quantitative Assessment of Annoyance|| |
People exposed to various levels of environmental noise experience various degrees of negative impact. The magnitude of this impact can be assessed through a social survey, where the respondents are asked to express their experience on a predetermined scale. This scale may be either a verbal scale with specific modifiers such as not annoyed , a little annoyed , very annoyed , etc . or a numerical scale with fixed end points that are defined by verbal modifiers, for instance: not annoyed and extremely annoyed .
The results from such surveys are commonly presented as dose-response functions showing the percentage of respondents that are annoyed to a certain degree, e.g., highly annoyed , as a function of noise dose expressed by the equivalent noise level or a similar quantity.
| Annoyance Score|| |
Instead of presenting the fraction of population that is annoyed to a certain degree, the annoyance score can be used as an alternative way of expressing annoyance versus noise exposure.
Subjective annoyance caused by exposure to a specific noise situation can be scored on a linear scale, 0 to 1, where "0" indicates not annoyed at all and "1" indicates extremely annoyed . This quantity, the annoyance score, thus denotes to what degree a person is annoyed by that particular noise situation. The annoyance score is often expressed in percent.
People's reactions to noise vary due to various reasons. If a group of people is asked about their annoyance response to a specific noise situation, the annoyance score for each individual can be averaged to give the group response or the mean annoyance score .
The results from social surveys on noise annoyance demonstrate that if the mean annoyance score is plotted against noise level expressed by an energy equivalent index such as L eq or L den , the resulting dose-response function can be approximated by a straight line for an extensive range of noise exposures.
Different noise sources cause different reactions. For a given value of L den , noise from rail traffic is less annoying than noise from road traffic, which in turn is less annoying than aircraft noise. In connection with environmental noise, this fact is often referred to as rail bonus and aircraft malus with respect to road traffic noise.
The dose-response functions presented in [Figure - 1] have been developed by HME Miedema and his colleagues at TNO  as part of the background information for the EU Directive on noise.  As can be seen in the figure, the dose-response functions for transportation noises are a set of nearly parallel lines spaced approximately 6 dB apart.
By using simple linear approximation, the annoyance score functions can be expressed by the following equation:
A = 1.58 (L den + k) - 62.25 [%]
where L den is the time-weighted equivalent level (in dB) and k is a source-dependent correction factor; e.g. k (aircraft) = +6 dB, k (road) = 0 dB, k (rail) = -6 dB. These correction factors correspond to the bonus and malus for transportation noise mentioned earlier. The equation is valid for the exposure range approximately 40-80 dB.
The simple linear equation for dose-response relationship shows that a certain change in noise exposure is related to a corresponding change in annoyance score regardless of the absolute level and type of transportation noise source. A 6 dB change in noise level gives approximately a 10% point change in annoyance score.
| Noise Impact in a Community|| |
The magnitude of noise impact in a certain area can be defined as the sum of annoyance scores experienced by all the residents within that area. This quantity is referred to as the noise annoyance index (in Norwegian: SPI = stψyplageindeks). The unit "1 SPI" thus equals "one extremely annoyed person." Due to the linearity of annoyance score function, 1 SPI would also represent two persons moderately annoyed (where annoyance score: A = 0.5), and so on.
It can be argued that this quantity is a better predictor of noise impact than, for instance, the percentage highly annoyed , which is commonly used, as the annoyance index also takes into account the annoyance experienced by all the persons that are annoyed to a lesser degree than "highly." A large number of people may be annoyed, but not necessarily highly annoyed . The SPI quantity includes these groups.
As an example, the total impact of annoyance caused by road traffic noise in Norway can be calculated as follows [Table - 1]:
- The noise exposure along every road has been estimated by using actual traffic data and standard prediction methods for road traffic noise.
- The number of people living within each 5 dB noise interval has been found from census data and registry of residences.
- The mean annoyance score for each exposure interval has been calculated for the mid-points (52.5 dB, 57.5 dB, etc.).
- The annoyance index per exposure interval is the product of number of people times mean annoyance score.
- The total annoyance index is the sum of annoyance index for all intervals.
Out of the total population of 4.5 million, more than 1.6 million are impacted by noise levels above L den = 50 dB, and the total impact from road traffic noise is equivalent to about "half a million extremely annoyed people."
| Noise from Different Sources|| |
There are no standard methods to compare annoyance caused by different noise situations when the noise is produced by different types of sources or by a combination of different sources. However, the international standard ISO 1996, Part 1, has a technical addendum that suggests a possible solution to this problem. In this method, each source is substituted by an equally annoying reference source (road traffic) by means of the annoyance score functions.
| Example|| |
A community of 500 residents is exposed to two different noise sources: aircraft noise at 55 dBA and road traffic at 60 dBA. The aircraft noise source at 55 dBA can be substituted by an equally annoying road traffic noise source at 61 dBA, based on the fact that there is a 6 dB aircraft malus when comparing with road traffic noise. These two road traffic noise sources, at 60 and 61 dBA, are added (energy) to give a total level of 63.5 dBA. The annoyance score associated with this level is 0.38, and the total noise annoyance index for this area is (500 x 0.38) = 190 SPI.
It should be stressed that the proposed method for assessing the environmental noise impact in a community has been developed for annoyance . In a noise survey, the recommended annoyance-reaction question is: How much does noise from (source) noise bother, disturb or annoy you? This is a subjective parameter that expresses a negative experience, and it is thus per definition health related. The method, however, cannot be used to assess other health effects that are related to noise levels in a non-linear way.
Cost of Noise Annoyance
Numerous attempts have been made to calculate a "cost" or to set a "price" on community noise annoyance. Factors that influence this "price" include the following:
- psycho-physiological effects, stress, etc.
- sleep disturbances (and resulting productivity loss)
- communication problems
- (possible) hearing damage
The price is likely to be reflected in a depreciation of property values. Studies have revealed that there is a linear relationship between noise level and change in property value (in Norway, roughly 0.5% per dBA). In other words, the change in value per decibel is independent of the absolute level. 
A similar relationship has been found for the annoyance score. A given change in noise exposure is related to a certain change in annoyance score regardless of absolute noise level or degree of annoyance. By using noise exposure data as a common parameter, it is possible to relate annoyance directly to a sum of money, and any given change in annoyance can be expressed in monetary terms.
In Norway, the "cost" of one extremely annoyed person (1 SPI) has been estimated to be approximately 1600 € per year. Due to the linearity explained earlier, the "cost" of a moderately annoyed person (0.5 SPI) thus equals 800 € per year. 
The annoyance index for Norway caused by road traffic noise, 503,388 SPI, corresponds to a cost of more than 800 million €. This relationship can be used for cost-benefit calculations. The national target for a reduction of community noise in Norway is a 25% cut in annoyance index. More than 200 million € can be spent each year in order to reach this goal, and still the effort would turn out to be "profitable."
| References|| |
|1.||Miedema HM, Oudshoorn CG. Annoyance from transportation noise: Relationships with exposure metrics Ldn and Lden and their confidence intervals. Environ Health Perspect 2001;109:4. |
|2.||Directive 2002/49/EC of the European Parliament and of the Council of 25 June 2002 relating to assessment and management of environmental noise . |
|3.||European Conference of Ministers of Transport. Efficient transport for Europe - Policies for internalization of external costs. Paris; 1998. |
|4.||SFT, (Norwegian Pollution Control Authority), Report 1714/2000, in Norwegian; 2000. |
SINTEF ICT, Trondheim
Source of Support: None, Conflict of Interest: None
[Figure - 1]
[Table - 1]