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CNOSSOS-EU stands for Common Noise Assessment Methods, which is a shared noise calculation method for EU member states. It is a European standard for noise calculations, encompassing road traffic, railways, industry, etc. CNOSSOS-EU (hereafter referred to as CNOSSOS) was initially developed by Kephalopoulos et al. (2012). Since then, the CNOSSOS model has undergone revisions, and the latest version is included in the Environmental Noise Directive (END) (2021), including all changes in the CNOSSOS method (Annex II), which should be referred to from now on. It is worth noting that since December 31, 2018, CNOSSOS has been mandatory for strategic noise mapping in the EU.

Source Module

In CNOSSOS' source module, a vehicle's sound power is a function of two factors: traffic speed and the frequency in octave bands. This means that the sound power emitted by the vehicle is determined in different frequency ranges spanning from 63 Hz to 8 kHz. Octave bands provide a way to categorize and study sound power levels at different frequencies. The coefficients for tire and engine noise, which determine the sound power level for tire and engine noise, are specified in (European Commission, 2021) (END, Annex II). These calculations assume a constant vehicle speed of 70 km/h, a flat and dry road surface consisting of a mix of Dense Asphalt Concrete (DAC) and Stone Mastic Asphalt (SMA) between two and seven years old, an air temperature of 20°C, and no studded tires.

If conditions deviate from the mentioned reference conditions, various types of corrections are applied. These corrections include adjustments for road surface type, slope, acceleration, and deceleration. Vehicles are divided into four categories: light vehicles (LDV), medium vehicles (MDV), heavy vehicles (HDV), and two-wheelers (motorcycles and mopeds). There is also an open category for future needs. Each vehicle is represented by a point source located 0.5 meters above the road surface. This point source is placed at the center of the vehicle.

Sound Propagation Module

CNOSSOS' sound propagation module is based on the French standard noise method NMBP-2008. It employs the principles of ray theory to calculate sound attenuation during its propagation from source to receiver. It considers two types of conditions: homogeneous atmospheric conditions and reflection conditions with downward bending of sound waves during propagation.

In the calculation of sound level, meteorological conditions such as air temperature and wind direction are considered. The calculations are performed under both homogeneous (favorable) and headwind conditions. Unfavorable conditions refer to headwind or calm wind situations. The calculations are done in the frequency range from 63 Hz to 8 kHz (octave bands) and up to a maximum distance of 2 km from source to receiver. The average sound level is determined by summing the levels under favorable conditions and homogeneous conditions, weighted by the probability of favorable conditions occurring.

CNOSSOS propagation module does not account for scenarios where sound propagates over water areas like lakes or rivers. The calculation procedure for sound propagation in CNOSSOS is described in the following section.

For each point source, the direction-specific sound power is determined, meaning that the sound power emitted from a specific location is calculated. Then, the probability of favorable conditions for each direction from source to receiver is estimated. Depending on the terrain, the propagation path is determined, which can be direct, reflected, or diffracted. For each path, attenuations under favorable and homogeneous conditions are calculated. These attenuations consider various factors such as the ground surface effect, geometric divergence, reflections from building facades, and diffraction corrections.

The concept of an average ground plane is used in ground effect attenuations in Nord2000. This approach replaces the actual ground with an imaginary plane representing the average profile of the ground. Applying this simplified concept calculates the sound level for each propagation path. These individual sound levels are then summed to determine the overall sound level at the receiver point. This empirical approach allows for more efficient calculations of ground effects in sound propagation.

Further details can be found in the following references.

References and Related Literature:

Khan, J., Thysell, E., Backalarz, C., Finne, P., Hertel, O., & Jensen, S.S. (2023). Performance Evaluation of Nord2000, RTN-96 and CNOSSOS-EU against Noise Measurements in Central Jutland, Denmark. MDPI Acoustics, 5(4). Pp. 1099-1122. DOI: https://doi.org/10.3390/acoustics5040062.

Kephalopoulos S, Paviotti M, Anfosso-Lédée F. (2012) Common Noise Assessment Methods in Europe (CNOSSOS-EU). EUR 25379 EN. Luxembourg (Luxembourg): Publications Office of the European Union: JRC72550. Available online: https://publications.jrc.ec.europa.eu/repository/handle/JRC72550.

European Commission (2021). CNOSSOS-EU: Environmental Noise Directive (END) (Annex II). Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:02002L0049-20150702&from=en

Khan, J., Ketzel, M., Jensen, S. S., Gulliver, J., Thysell, E., & Hertel, O. (2021). Comparison of Road Traffic Noise prediction models: CNOSSOS-EU, Nord2000 and TRANEX. Environmental Pollution, 270, 116240. DOI: https://doi.org/10.1016/j.envpol.2020.116240.