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Focus: acoustic evaluation of the ‘car-free sunday’ action

Once a year the 'In Town Without My Car!' day is held. On this 'car-free Sunday' car traffic is prohibited between 9 a.m. and 7 p.m. From the acoustic assessment of this action it appears that the levels of background noise on these Sundays are considerably lower than on other Sundays.

'In Town Without My Car!', a European initiative

In Belgium a 'car-free Sunday' has been organised every year since 2000 on the Sunday of the European mobility week. In the Brussels Capital Region car traffic is prohibited between 9 a.m. and 7 p.m. that day. An exception applies to some vehicles (e.g. public transport, emergency services, etc.); these can travel, but not faster than 30 km/hour.
The first edition of this day took place in 2000, several 'comfort zones' were set up in three municipalities of the Brussels Capital Region. The next year, a number of other municipalities followed their example. Since 2002 the entire region has been closed to traffic between 9 a.m. and 7 p.m on the car-free Sunday.

Assessment of the impact on the sound environment

To be able to assess the environmental impact of this action, Bruxelles Environnement-Leefmilieu Brussel carries out measurements of air and noise. The results of these measurements are compared to equivalent periods with normal traffic.
Specific measurement campaigns were set up in 2000 and 2001 to map the noise nuisance. Since then, the assessment makes use of the noise levels that are measured continuously by the permanent noise monitoring network: it concerns 5 measuring stations (out of a total of 17) that are strongly affected by road traffic noise. As the methodology for temporary measurements is different from the one used at the permanent stations (location of the monitoring, duration and time of the measurement, etc.), the results showed below only consider the years 2002 to 2012 and are derived from the permanent stations only.
One of the indices chosen to characterise the noise environment is the noise index LA90. This index indicates the levels of background noise and is generally influenced greatly by road traffic. It is calculated, on the one hand, per one-hour period, and, on the other hand, for the total duration of the action (9 a.m. to 7 p.m.) and compared to the previous Sunday with normal traffic.

A considerable drop in noise levels

Background noise levels are generally lower on the car-free day, regardless of the measurement location. This significant drop differs between locations, it is particularly pronounced in areas where traffic volume and speed are usually high.
Background noise level

At the monitoring point AUD_E411, located very close to the E411 motorway, the average drop is considerable (more than 20 dB(A)). The sound environment in this normally noisy area is now quiet. At monitoring point AUD_Wavr a very marked drop is recorded (greater than 10 dB(A)). At monitoring points LKN_Houb and WSL_Gull the drop in the noise level is quite pronounced (8 to 10 dB(A)).
At monitoring point Saint-Gilles, which is characterised by moderate to local traffic, the drop is less significant, but still noticeable to the human ear (around 4 dB(A)).
The plot representing the change, hour per hour, of the LA90-indices shows a clear drop in the background noise level between 9 a.m. and 7 p.m. on the car-free Sunday, as compared to the previous Sunday. Depending on the monitoring station, the difference between both days is smaller or greater. The most significant decrease was recorded in 2012 at the monitoring station located near the E411 motorway:
Station E411
Hence, by means of noise measurements it is possible to immediately and objectively illustrate the drop in noise levels as a result of the limitation or interruption of car traffic.
However, noise is only one aspect of the nuisance caused by car traffic. Other effects, such as 'perception' by residents and users, reduced emissions of certain air pollutants, etc., are also studied. They all contribute to the success of these 'car-free days'.

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Date de mise à jour: 30/11/2015