Nord2000 was introduced by the Danish Environmental Protection Agency (EPA) in 2006. It is widely used for the strategic mapping of road and railway noise. Nord2000 can predict 1/3-octave band levels, for example, for road noise, spreading over complex terrain in nearly all-weather conditions. This enables the calculation of annual average noise levels, as required by European directives on environmental noise. Since July 2007, the Danish EPA has recommended Nord2000 as Denmark's official method for calculating road and railway noise. In addition, the annual noise average Lden (day-evening-night noise) was introduced as the Danish noise indicator to assess the population's exposure to traffic noise.
The Nord2000 method is a point-to-point approach. Its source module (Jonasson, 2006) estimates sound power levels for tire/road and engine noise in 1/3-octave bands from 25 Hz to 10 kHz. Nord2000 calculates the sound power level for tire/road and engine noise separately. Corrections are applied to account for how a wet road surface affects tire noise from light vehicles, although such corrections cannot be made for noise from heavy vehicles due to insufficient data. Nord2000 also incorporates corrections for road surface types, gradient, acceleration/deceleration, and temperatures different from 20°C when evaluating tire noise. Corrections for engine noise related to acceleration/deceleration and road gradients are also specified.
The source module distinguishes between (i) light, (ii) medium, and (iii) heavy vehicles. The source module is further described in Jonasson (2006).
Sound Propagation Module
Nord2000's sound propagation module uses geometric ray theory to calculate sound attenuation (1/3-octave bands, 25 Hz to 10 kHz) along the propagation path. The model considers terrain shape, soil type, and other relevant factors in the calculations (Danish Road Directorate, 2011). The terrain cross-section is divided into linear segments assumed to be flat unless otherwise specified by indicating the value for surface roughness (Khan et al., 2021). Each of these segments contributes to ground and shielding effects, resulting in comprehensive and precise calculations.
The propagation module in Nord2000 incorporates the use of Fresnel zones to account for ground effects. Fresnel zones are further described in Plovsing (2006 a, b). The ground effect is assessed for each surface type within the Fresnel zone, and the effect is determined as a weighted average, considering the proportion of the Fresnel zone covered by each soil surface. Eight classes of soil surfaces are defined, ranging from very soft (like grass) to very hard (asphalt or concrete). However, typically only two classes, "soft" and "hard," are used for noise mapping purposes. Each class is characterized by a representative value for flow resistance.
Nord2000 is designed to calculate annual average noise levels, considering different weather conditions and their impact on attenuation. To achieve this, different weather classes are defined, and their frequency is determined using 10 years of observational data for a meteorological reference year (Eurasto, 2005). Each weather class is characterized by a sound speed profile as a function of height above the ground. Calculating the annual average noise level involves determining the noise level contributions for each weather class and then combining these levels, considering their frequency.
Nord2000 is built on comprehensive testing and validation. The Danish Road Directorate has released reports documenting the model's evaluation, testing, and improvements. Interested readers are referred to relevant reports and articles for a deeper understanding of the model's structure, relevant concepts, and evaluations.
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.
Danish EPA (2006). Nord2000: Nordic noise prediction method. Available online: https://tinyurl.com/2rjz8euf.
Danish Road Directorate (2011). Traffic noise prediction with Nord2000 – An Update. Available online: https://tinyurl.com/mvw7d69k.
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.
Jonasson, H.G. (2006). Acoustic Source Modelling of Nordic Road Vehicles, SP Rapport 2006:12, Energy Technology, Borås, Sweden.
Plovsing, B. (2006a). Nord2000. Comprehensive Outdoor Sound Propagation Model. Part 1: Propagation in an Atmosphere without Significant Refraction, DELTA Acoustics and Vibrations (now FORCE Technology), Hørsholm, Denmark. Report # AV 1849/00, revised.
Plovsing, B. (2006b). Nord2000. Comprehensive outdoor sound propagation model. Part 2: Propagation in an atmosphere with refraction. DELTA Acoustics & Vibration (now FORCE Technology), Hørsholm, Denmark. Report # AV 1851/00.
Eurasto, R. (2005). Nord2000 for road traffic noise prediction. Weather classes and statistics, VTT Research Report No. VTT-R-02530-06, Esbo, Finland.
Kragh, J. (2006). Nord2000: User's Guide Nord2000 Road. DELTA Acoustics and Vibrations (now FORCE Technology). Report # AV 1171/06 Hørsholm, Denmark.