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The population's exposure to noise
The potential exposure of the population was evaluated on the basis of the noise registers drawn up for road traffic (2006), rail traffic (2006) and air traffic (2014). Road traffic is the noise source affecting the largest number of Brussels inhabitants, with noise from rail traffic affecting them the least. Almost one in ten inhabitants would have been exposed to loud or even very loud levels of noise, due to road traffic alone. With regards to air traffic, the number of inhabitants exposed was generally higher in 2014 compared to 2010, however without these being excessive noise levels.
Transport noise related to road traffic, rail traffic and air traffic
The environmental challenges in the Brussels-Capital Region are sizeable: the development of the city and of the accompanying human activities needs to be reconciled with a satisfactory quality of life for the inhabitants (around a million people), in particular by minimising the environmental nuisances.
To assess the noise nuisance in the living environment of the inhabitants of Brussels, an ‘acoustic’ site description of the territory was made for the reference year 2006 for road and rail noise and 2014 for aircraft noise. The purpose of this site description is to quantify the ‘structural’ noise from the main sources of noise, i.e. the different modes of transport (road, air and rail) and to model the population's exposure.
Compared to the previous detailed report on the State of the Environment, only the situational analysis of the noise related to air traffic has been updated. The situations regarding road traffic and rail traffic will be updated in 2017 based on the 2016 situation.
Assessment of the population's exposure to noise
The population's exposure was modelled in particular for two noise indicators:
- the Lden indicator (the day-evening-night level), which represents the weighted noise level over 24 hours. For the weighting, a penalty factor of 5 dB(A) is applied during the evening (7 p.m. to 11 p.m.) and of 10 dB(A) during the night (11 p.m. to 7 a.m.), as noise at those times is experienced as a greater annoyance;
- the indicator Ln (the night level), which represents the noise level at night between 11 p.m. and 7 a.m.
The resulting maps of these modelling are called the ‘noise register’.
The population's exposure to noise was then estimated according to the place of residence and the exposure of buildings with a façade potentially subject to a given level of noise (considering the most exposed façade in the case of road and rail noise).
It should be made clear that this is an estimate of the people potentially exposed (i.e. the residents) to an exterior noise level and not of actual exposure data measured inside buildings. In order to put these exposure results into perspective, an additional indication is provided with the proportion of the population living in dwellings with a ‘quiet façade’ where noise levels are 20 dB(A) less than on the most exposed façade (this concept is not relevant to air traffic noise as aircraft fly over the entire building).
Scale of exposure of the population to transport-related noise
Proportion of the population living in dwellings exposed to transport noise (road, air and rail) in the Brussels-Capital Region
Sources: Brussels Environment, 2010, "Bruit des transports, cartographie stratégique en Région de Bruxelles-Capitale", for road and rail noise, based on traffic data from 2006 and population data from 2003 (992,300 inhabitants) & Brussels Environment, 2015, "Cartographie du bruit du trafic aérien en Région de Bruxelles-Capitale", for air traffic noise, based on traffic data from 2014 and population data from 2012 (1,138,854 inhabitants)
The results show that road traffic is the noise source that affects the greatest number of people in Brussels, followed by air traffic and then rail traffic.
It should be specified that some people in Brussels are simultaneously exposed to more than one noise source ("multiple exposure"), in which case the noise energy from the different sources is combined. The concept of the "quiet façade" must therefore be interpreted with caution: a façade can be quiet relative to one noise source, but "noisy" relative to others. The results presented below derive from the analysis of each noise source taken individually and not from an analysis of multiple exposure.
Potentially, nearly 43% of the inhabitants are likely to experience a significant auditory annoyance (corresponding to Lden levels exceeding 55 dB(A), which is the threshold at which the noise environment is classified as "relatively noisy") due to road traffic noise; just 16% of this group live in a dwelling with a quiet façade. Conversely, less than one in ten are likely to experience noise annoyance associated with air traffic (7%) or rail traffic (4%, of which 22% have a quiet façade).
In addition, nearly 11% of the inhabitants are potentially exposed to road noise levels above 65 dB(A), which is the threshold at which the noise environment is classified as "noisy" (for the sake of comparison, the intervention threshold for this noise source is fixed at 68 dB(A)). Most of these people (58%) do not have a fallback position in the form of a quiet façade. This proportion is ten times less in the case of railway noise (1%, half of whom have a dwelling with a quiet façade), and close to zero in the case of air traffic noise.
However, it should be noted that 0.2% of the Brussels population is potentially exposed to a noise level of more than 75 dB(A). Road traffic is the only responsible for reaching such levels (Lden), which are observed in the immediate vicinity of motorways and the inner and outer ringroads. Fortunately, nearly three-quarters of the inhabitants concerned have quieter rooms.
Transport-related noise annoyance affects more people at night. This does however not apply to the extreme noise levels.
Thus, comparing the different modes of transport, it is interesting to note that the threshold at which sleep disturbance is considered moderate to severe by the WHO (Ln greater than 45 B(A)) is exceeded for 47% of the Brussels residents due to road noise alone, 17% due to air traffic noise alone and 4% due to rail traffic noise alone. Moreover, a mere 14% of the people exposed to these levels of road noise have the benefit of quieter surroundings (i.e. a quiet façade).
It can also be noted that the percentage of the exposed population above this limit for air traffic noise alone was 8 points higher in 2014 compared with 2010 (17% vs 9%). However in 2014, a new dispersal plan was implemented for flights taking off from Brussels Airport. Following the implementation of this plan, numerous neighbourhoods, including some densely populated areas, were flown over by aircraft whereas this was not the case previously. The choice of air routes is therefore likely to have direct repercussions in terms of the exposed population.
In addition, nearly 4% of the Brussels residents are potentially exposed at night to a noise level (Ln) associated with road traffic that exceeds the value of 60 dB(A), which is the intervention threshold defined at regional level. Slightly more than half of these (54%) have a quiet façade with respect to road noise.
For rail traffic, the proportion of residents affected by night noise in excess of this threshold is 0.5%, around three-quarters of whom have a quiet façade with respect to train noise. Air traffic does not affect anyone beyond this threshold.
When examining the presented results, one must bear in mind the subjective character of noise perception. People's perception of their noise environment also depends on parameters other than their level of exposure (such as the noise source, the time of day but also people's personal characteristics and the condition of their home).
State of the Environment’s sheet(s)
Other publications from Brussels Environment
Cartographie du bruit du trafic aérien en Région de Bruxelles-Capitale – Période étudiée : année 2009, 2010 (.pdf, in French only), restricted
Study(ies) and report(s)
ACOUPHEN ENVIRONNEMENT, 2009. « Cartographie stratégique du bruit des transports terrestres en Région de Bruxelles-Capitale – année 2006 – Résumé non technique ». Study performed on behalf of Brussels Environment, 34 pp. (.pdf, in French and Dutch only)