PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Implementation of CNOSSOS-EU method for road noise in Italy
Gonzalo DE LEÓN1*; Francesco FIDECARO1; Mauro CERCHIAI2; Marco REGGIANI2; ElenaASCARI and Gaetano LICITRA2
1
2

Pisa University, Physics Department, Italy

Regional Agency for Environmental Protection of Tuscany (ARPAT), Italy

ABSTRACTThe European Directive 2015/996 describes the common methods (CNOSSOS-EU) for the determinationand management of environmental noise at European level, providing guidelines for a harmonized approachfor Member States. CNOSSOS-EU includes different emission data for road, railway and industrial noiseand provides a common model for sound propagation. The emission model was derived to be valid underreference conditions in terms of meteorology and traffic as detailed in the reference report by the Joint
Research Centre (JRC) of the European Commission. In order to take into account situations that differ fromthe reference one, appropriate corrections were also offered. For a correct application on a local scale, thedefault values suggested by CNOSSOS-EU are required to be redefined in order to more adequately describe
the Italian reality (i.e. car fleet, surfaces, climate conditions, etc.). Regional Agency for Environmental
Protection of Tuscany (ARPAT) carried out specific measurements campaigns to acquire data useful tovalidate the methods for Italian conditions. Regression coefficients used in the emission model, wererecalculated from campaigns in different sites carefully chosen to resemble the reference conditions.
Keywords: emission, database, CNOSSOS

1. INTRODUCTION
Directive 2015/996 (1) describes the common methods for determination and assessment ofenvironmental noise at European level, providing guidelines for a harmonized approach of theMember States in order to identify priorities for action planning (aimed to reduce or avoid exposure
to harmful noise levels) and by the European Commission (EC) to assess the number of people
exposed to noise and to inform the general public about it.
These methods called "CNOSSOS" include separate calculation approaches for the emission ofroad, rail and industrial sources. Differently there is a common model for the propagation from thesource to the environment. For aircraft noise, a separate emission and propagation model is defined,
based on the ECAC Doc 29 requirements.
Particularly, for the noise produced by road infrastructures, the European intervention policies
include, first and foremost, the progressive reduction of sound emission levels generated by vehicles
and the interaction of tyres with road paving, therefore the intervention on the source is prioritized at
the moment of the rehabilitation interventions.
The emission model was obtained from experimental measurements based on data sets of 4 – 10years old in the framework of the IMAGINE – Harmonoise project (2). As a result, a set of soundpower coefficients were obtained by means of regression analysis.
However, in the last years either the car fleet as the engineering technologies on pavement surfaces
have evolved, therefore the coefficients proposed may have become obsolete. For a correct application
on a local scale, the default values suggested by CNOSSOS-EU are required to be redefined in orderto more adequately describe the Italian reality.

1*

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gonzalo.deleon@df.unipi.it

2. CNOSSOS-EU
2.1 Emission Model
The sound power is calculated separately for the rolling noise generated by the interaction between
the tire and the road 𝐿#$ %, ' , and for the propulsion noise 𝐿#( %, ' generated by the exhaust, engine,change of gear, etc.
𝑣'
+ ∆𝐿5$,%,' (𝑣' )
𝑣23%

(1)

𝑣' − 𝑣23%+ ∆𝐿5(,%,' (𝑣' )
𝑣23%

(2)

𝐿#$ %, ' = 𝐴$,%,' + 𝐵$,%,' ⋅ 𝑙𝑜𝑔
𝐿#( %, ' = 𝐴8,%,' + 𝐵(,%,' ⋅Where the 𝑣23% is set at 70 km/h and the coefficients 𝐴$,%,' and 𝐴8,%,' automatically assumes themeaning of average sound power level at the reference speed for the vehicle category in consideration,
while the coefficients 𝐵$,%,' and 𝐵8,%,' determine the speed dependence. ∆𝐿5$,%,' and∆𝐿5(,%,' correspond to the sum of the correction coefficients to be applied to the noise emission for
specific conditions of the road or vehicle that deviate from the reference one.
CNOSSOS (3) provides four main categories of vehicles regarding their characteristics of noise
emission. For the calculation of noise propagation and for the determination of sound power emission,
it is necessary to describe the source with one or several point sources. In this method, each vehicle(category 1, 2 and 3) is represented by one single point source. As depicted in Figure 1, this point
source is placed 0.05 m above the road surface

Figure 1 – Location of equivalent point source
The source equations and coefficients are derived to be valid under reference conditions in termsof meteorology and traffic.
2.2 Sound Power Coefficients
The sound power coefficients 𝐴$ , 𝐴( , 𝐵$ and 𝐵( for Eq. 1 and 2 have been obtained in the project
IMAGINE (2). The distribution between rolling and propulsion contribution, was obtained bydifferent measurement systems, i.e. on-board, coast-by or pass-by on test tracks and then calibratedusing roadside pass-by measurements performed in different areas in the EU.
The IMAGINE model used a different source height composition:• One source at 0.01 m height, to which 80% of the rolling noise and 20% of the propulsion
noise was attributed.
• One source at 0.30 m height, for light motor vehicles and powered two-wheelers, or 0.75 m
height for (medium) heavy vehicles, to which 20% of the rolling noise and 80% of the
propulsion noise was attributed.
2.3 Free Field Propagation Model
The noise propagation model proposes the following equations concerning the different types ofattenuation. The attenuation due to geometrical divergence, 𝐴𝑑𝑖𝑣 corresponds to a reduction in thesound level due the propagation distance:(3)
𝐴<=> = 20⋅ 𝑙𝑜𝑔 𝑑 + 11
where 𝑑 is the distance in meters between the equivalent source and the receiver. This equation regards
to a point source in free field, with spherical divergence.
For the attenuation factor due to the absorption of the ground the following formulation have been
proposed in the guidelines:
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𝐴B2CDE< = 𝑚𝑎𝑥 −10 · 𝑙𝑜𝑔 4

𝑘L
𝑑8L

𝑧NL −

2 𝐶%
𝐶%
𝑧 +
𝑘 N
𝑘

𝑧2L −

2 𝐶%
𝐶%
𝑧 +
𝑘 2
𝑘

, −3(1 − 𝐺 R 8STU )(4)

Recently, the Netherlands National Institute for Public Health and the Environment (RIVM) havepublished a series of amendments for the CNOSSOS-EU (4). Among them, a correction in the
𝐴B2CDE< formula was provided and new sound power coefficients suggested. For the 𝐴𝑔𝑟𝑜𝑢𝑛𝑑 theboundaries established by the term −3(1 − 𝐺 R 8STU ) in Eq. 4 was replaced by 𝑅 in the Eq. 8
𝐴B2CDE< = 10⋅ 𝑙𝑜𝑔 10Z([\,] ^[\,_ )/La + 10Z[b /ca
𝐴d = 20 − 3⋅ log

(5)

𝑑8
𝑓
− 10⋅ log
1000
100

(6)

𝐴i = 20⋅𝑙𝑜𝑔 1 + 𝐶𝑅

(7)

𝑅 = min (max 𝑅% , 𝑅'=E = −0.9 , 𝑅'Sq = 0.4)
(8)Further studies proposed a simplification of the 𝐴B2CDE< formula based on the coherent addition of
the direct and reflected sound waves (5).
𝐴B2CDE< = −20⋅𝑙𝑜𝑔 1 +𝑅c⋅cos(k⋅(𝑅c -𝑅L ))𝑅L(9)where 𝑅c and 𝑅L are the direct and reflected distances in meters. For further details, refer to (6), theofficial document of the method (3), and their amendments (4).
2.4 Transfer Function
In order to estimate the sound power levels from roadside measurements a proper transfer function
was needed. In general, if the sound pressure is acquired for a single event, the associated sound power
must be integrated along the time period 𝑇 when the sound source pass-by is measured.
TL

10{|(T) ca 𝑑𝑡

𝑆𝐸𝐿8SNNZyz = 10 · log

(10)

Tc

𝐿8 (𝑡) = 10 · 𝑙𝑜𝑔ca

𝑊
𝑊C+ 10 · 𝑙𝑜𝑔ca

1
𝑊C+ 10 · 𝑙𝑜𝑔ca 𝐷𝐼 + 10 · 𝑙𝑜𝑔ca 𝜌C 𝑐 L − 𝐴B2CDE< (𝑡)4𝜋𝑟(𝑡)L𝑝C(11)

Considering that at 𝜏 = 15 °𝐶 and considering 𝜌C = 1.225 𝑘𝑔/𝑚 ˆ , 𝑐 = 340.5 𝑚/𝑠, then the terms
𝜌C 𝑐

5Š

8Š ‹

≈ 1 and 10 · 𝑙𝑜𝑔cac•Ž≈ −11.

Finally:TL

𝑆𝐸𝐿8SNNZyz = 10 · 𝑙𝑜𝑔ca

10{• ^ca·•CBc^ca·•CB d‘ ZccZ𝐴𝑔𝑟𝑜𝑢𝑛𝑑 (T)
2‹ T

ca

· 𝑑𝑡

(12)

Tc

3. Methodology
Several sites were chosen with the premise to be sufficiently close to the source in order to carryout roadside Statistical Pass-By measurements (7), from now on called "SPB". Whenever it waspossible the microphone was located at a distance equal to 7.5m from the road centreline and 4mheight. Figure 2 shows the optimal set-up.
The SPB method is based on energy measurements associated with the passage of a single vehicle
on a significant statistical sample. For each single event the time history of the levels, the spectrumin octave bands, the speed, the direction of travel and the distance between the axes, are acquired.
From an operational point of view, for each single passage and for each octave band, the single
event level (𝐿[’ ), from now on called (𝑆𝐸𝐿), was acquired on the entire time interval in which thesignal exceeded the value of 𝐿'Sq − 10𝑑𝐵. For simplicity at the time of identifying the events, nighttime measurements were analysed, where the vehicular flow was lower and the single events spaced
over time.
For the classification of vehicle categories and the 𝑣23% , a statistical approach was used on the
distribution of distances between the measured axes and the speed distribution.
Regarding the weather data, the measurements days with rain and/or excessive wind (over 5 m/s),that could have influenced the results, were discarded.
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For each experimental set-up and for each single event the different transfer functions were solvedin order to obtain the sound power level at different heights from the 𝑆𝐸𝐿 measurement. The obtained
values were corrected for temperature.
Once the events were identified, classified by category, and the sound power levels calculated, atechnique called “ 𝜒 L − 𝑏𝑖𝑛𝑛𝑒𝑑 𝑓𝑖𝑡” was used. Based on this procedure, the data was grouped intoclasses according to particular algorithms and each class was represented by a central value and an
uncertainty associated, according to the distribution of data within each class (8).
Finally, the power levels were distributed proportionally in rolling noise and propulsion with two
different approaches based on the quantity of the equivalent sources and their heights.

Figure 2 – Experimental set-up

4. Results
4.1 Transfer Functions
Following the above mentioned methodology, the critical aspect in this study was the resolutionof the Transfer Function (from now on called 𝑇𝐹). Recalling the Eq. 12
TL

𝑆𝐸𝐿8SNNZyz = 10 · 𝑙𝑜𝑔ca

10{• ^ca·•CBc^ca·•CB d‘ ZccZ𝐴𝑔𝑟𝑜𝑢𝑛𝑑 (T)
2‹ T

ca

· 𝑑𝑡

(13)

Tc

For simplicity’s sake the 𝐷𝑖𝑟𝑒𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝐼𝑛𝑑𝑒𝑥 𝐷𝐼 was assumed constant 𝐷𝐼 = 1, congruent with the
hypothesis for an omnidirectional point source. For each single vehicle moving along the line in frontof the microphone with a constant speed, the position 𝑥c at the instant 𝑡c and 𝑥L at 𝑡L are known. This
allowed to introduce a change of variable.
𝑥L − 𝑥c = 𝑥 = 𝑣𝑇

(14)𝑑𝑥 = 𝑣𝑑𝑡

(15)

L

L

L

𝑟 (𝑡) = 𝑟C + 𝑥
being 𝑟C the minimum distance between the source line and the microphone.
𝑆𝐸𝐿8SNNZyz = 𝐿5 + 10 · log

1
𝑣

q‹

‹

10 Zca·š›œ 2Š ^q‹ Zcc Z𝐴

𝑔𝑟𝑜𝑢𝑛𝑑 (2Š‹ ^q ‹ ) /ca

q•

(16)

· 𝑑𝑥

(17)

As detailed before three different formulations to consider the ground attenuation A œŸ› ¡¢ werestudied, obtaining three different 𝑇𝐹 for each source height (0.01, 0.05, 0.3 and 0.75 m) with a fixed
4 m height receiver. Figure 3, Figure 4 and Figure 5 shows the 𝑇𝐹 in 1/1-octave bands, at 70 km/h andfor a view angle of 160°.

Figure 3 –Transfer Function using Eq. 4 for the 𝐴B2CDE<

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Figure 4 –Transfer Function using Eq. 5 for the 𝐴B2CDE<

Figure 5 –Transfer Function using Eq. 9 for the 𝐴B2CDE<
4.2 Sound Power Coefficients
Following the proposed work flow, once the 𝑇𝐹 were obtained, the “𝜒 L − 𝑏𝑖𝑛𝑛𝑒𝑑 𝑓𝑖𝑡” technique
was applied. This procedure lies on a poissionan approach for the estimation of the uncertainty basedon the count inside each bin, but this is useful when the number of occurrences is small. This is the
typical case of the edge bins. Finally, the distribution of the sound power levels into rolling andpropulsion components was carried out. Two different approaches were studied:
The first one consisted to use the source height composition as proposed in IMAGINE (2), for thisapproach the three transfer functions with the coherent addition of the direct and reflectedrays 𝑇𝐹a.ac , 𝑇𝐹a.ˆa and 𝑇𝐹a.£¤ were used to calculate the correspondent sound power levels, then thecontributions were added as explained in 2.2.
The 2 nd approach consisted to calculate the sound power levels at 0.05 m with the 𝑇𝐹a.a¤
assuming that the sound power of the source includes the possible effects of reflection on the surface
immediately below the real source and in a specific direction in space, then the distribution into rollingand propulsion noise as proposed in CNOSSOS was carried out.
Figure 6, Figure 7 and Figure 8 shows the results for rolling, propulsion and total sound power
levels for each category. In each graphic are plotted, the sound power levels obtained with the 1 st
approach called with the label “TF coherence, the sound power levels obtained with the 2 nd approach andusing the Eq. 5 called with the label “TF Amendments”, the sound power levels obtained with the 2 nd
approach and using the Eq. 4 called with the label “TF CNOSSOS ”, the sound power levels suggested by
CNOSSOS with an extra 3 dB addition with the label “CNOSSOS Original Coeff +3 dB” and thesound power levels suggested by the new amendments with the label “CNOSSOS Amendments
Coeff”.

Figure 6–Rolling, propulsion and total sound power levels for category 1

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Figure 7–Rolling, propulsion and total sound power levels for category 2

Figure 8–Rolling, propulsion and total sound power levels for category 3
The final coefficients for each category in 1/1-octave band obtained with the “TF Amendments” andthe 2 nd approach are presented in Table 1, Table 2 and Table 3.
Table 1 – Coefficients for category 1
63 Hz

125 Hz250 Hz500 Hz1000 Hz2000 Hz

4000 Hz

8000 Hz

AR

85.1

86.8

88.6

94.5

101.2

96.4

84.6

74.9

BR

40.3

42.3

32

26.5

35

39.6

41.8

44.2

AP

99.7

90.3

92.2

89.9

88.1

89.4

83.7

76.5

BP

3.2

8

5.4

9.3

8.8

8.8

9.1

9.9

Table 2 – Coefficients for category 2
63 Hz

125 Hz250 Hz500 Hz1000 Hz2000 Hz

4000 Hz

8000 Hz

AR

91.4

97.8

99.3

98.0

96.9

86.2

78.3

73.5

BR

57.4

53.7

46.6

35.1

44.6

44.8

42.2

45.5

AP

108.2

105.6

106.5

98.1

98.1

90.4

83.3

75.8

BP

9.0

10.8

10.4

10.2

11.9

9.6

7.7

8.0

Table 3 – Coefficients for category 3
63 Hz

125 Hz250 Hz500 Hz1000 Hz2000 Hz

4000 Hz

8000 Hz

AR

94.1

93.8

97.3

104.2

103.8

96.1

88.2

84.3

BR

49.8

30.4

9.7

30.4

38.7

34.5

28.8

31.3

AP

111.9

102.9

105.2

104.5

103

97.8

92.4

87.2

BP

12.2

4.2

-3.9

7

8.3

3.5

1.2

0.9

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5. Discussions
5.1 Sound Power Coefficients
It has been shown in several studies that CNOSSOS-EU gives an underestimation of the noiselevels up to 3 dB, this is explained because the source power coefficients were derived in the
IMAGINE project with a different source composition as explained in 2.2. The problem lies in thefact that the propagation model was switched, and the equivalent source changed from to two to one.
The CNOSSOS model adopts equivalents point sources being all mutually incoherent, while in the
IMAGINE project coherent addition of the sources was assumed. In CNOSSOS the phrase "The soundpower of the source includes the possible effects of reflection on the surface immediately below thereal source and in a specific direction in space", implies that the presence of the reflective surface
leads to a doubling of sound energy and an increase of the sound power of 3 dB.
For category 1 is known that at higher speeds, over 50 km/h, the contribution of noise is mostly aconsequence of the tyre/road interaction and the aerodynamic noise, both considered in the rollingnoise. This effect is consistent with the distribution assumed for light vehicles in the 2 nd approach.
When using the 1 st approach for this category, the ground effects originated from the interference
between direct and reflected path are strongly affected by the composition and variation in sourceheight. For the propulsion noise it was considered a contribution of the 80% from the source at 0.30
m and 20% from the source at 0.01m. It can be observed in Figure 5 that there is a 7 dB difference
between the the two sources in the frequency range between 500 and 2000 Hz, this produced an
overestimation on the propulsion and the total sound power levels. Regarding the new formulation totake into account the grounds effects a slightly difference can be appreciated in the propulsion
contribution, however as explained before the mainly contribution in this category comes from rollingnoise.
For category 2 the methodology for classification exposed an important issue, a mixture between
vehicles from category 1, 2 and 3. A deeper analysis showed two main clusters, the one with the lower
slope after the “𝜒 L − 𝑏𝑖𝑛𝑛𝑒𝑑 𝑓𝑖𝑡” was chosen. It can be seen that the propulsion noise is predominant
specially for low speeds. Considering that the speed range from the analysis is from 60 to 100 km/h,
the proposed coefficients differ consistently in cases outside this range. Regarding the newamendments formulation, the results show a similar slope to the one obtained taking into account thecoherence between direct and reflected waves.
For the category 3, the 2 nd approach assume a predominant influence of the propulsion noise on
the lower speed range and an inversion at the higher ones. Regarding the 1 st approach, the sourcecomposition was assumed with the higher source at 0.75 m. As mentioned before this upper source
have a bigger impact but at this particular height the peak is shifted to the lowers frequencies. It is
important to highlight that higher sound power levels were expected, instead the results obtained forheavy vehicles were slightly lower than the ones proposed in the amendments. Again the range in
speed is limited to 60 to 95 km/h.
Finally, we can appreciate that the results obtained with the 2 nd approach for light and heavy
vehicles are similar to the ones calculated with the original values with an addition of +3 dB.
5.2 Ground Attenuation
The latest amendments proposed a modification to the ground attenuation factor. In Figure 3 andFigure 4 the difference on the Transfer Function using one or another formulation can be observed,
but these TF are a result of an integration along the distance travelled when the pass-by vehicle ismeasured, therefore the differences don’t stand out. Remembering that the propagation model works
on a point to point basis, Figure 9 is presented in order to elucidate the distinction between the newand the old formulation. The figures represent the ground attenuation factor as a function of the
distance and frequency. It can be appreciated that the inferior boundary is represented by a flat surface.
In the original formulation this surface was wider in the frequency range, up to 1000 Hz, and also in
distance up to 40 m. Furthermore, in the new amendments the limit was reduced only to the lower
bands, up to 125 Hz. Another observation is that peak was reduced in intensity and shifted infrequency, where in the original formulation the peak was up to 16 dB now is reduced at almost 8 db.
Lastly, the ground effect is now wider than before affecting the whole frequency spectrum.

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Figure 9–Attenuation Ground as a function of distance and frequency with Eq. 5 (left) and Eq. 4 (right)

6. Conclusions
Directive 2015/996 describes the common methods for determine and assess environmental noise
at European level, providing guidelines for a harmonized approach of the Member States. These
procedures called "CNOSSOS" include separate calculation methods for the emission and the
propagation.
The emission model was obtained from experimental measurements based on data sets fromIMAGINE project. As a result, a set of sound power coefficients were obtained by means of regression
analysis. In this framework, the source composition was different, but in CNOSSOS the propagation
model was switched, and the equivalent source changed from to two to one. This mismatch between
the emission and the propagation model led to an underestimation of the noise levels up to 3 db.
For a correct application on a local scale, the default values suggested by CNOSSOS-EU arerequired to be redefined. A special methodology to derive the sound emission coefficients from
regression analysis from the measurements was carried out. This methodology consisted to calculate
the correspondent Transfer Function for each vehicle pass-by and then perform a “𝜒 L − 𝑏𝑖𝑛𝑛𝑒𝑑 𝑓𝑖𝑡”.
The sound power levels were obtained using three different Transfer Functions considering theinfluence of the ground effect in different ways. Then the sound power levels were distributed torolling and propulsion noise proportionally. Final results for category 1 and 3, using the “TF Amendments”
presented a similar trend to the original coefficients suggested with a difference of +3 dB.

ACKNOWLEDGEMENTS
All the measurements were carried out by the Regional Agency for Environmental Protection of
Tuscany (ARPAT). Special acknowledgments to Paolo Gallo, Marco Reggiani, Mauro Cerchiai, Elena
Ascari and specially Gaetano Licitra. This paper could not have been done without their support.

REFERENCES
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11 of the IMAGINE project. IMAGINE project, 11.
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Europe (CNOSSOS-EU). Common noise assessment methods in Europe (CNOSSOS-EU), 180-p..
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