The tire/road noise comparison of SMA 11 and cobblestone pavement Blanka Hablovicova 1 Petra Markova 2 Vitezslav Krivanek 3 Transport Research Centre CDV Lisenska 33a, 636 00 Brno, Czech Republic

ABSTRACT Noise has a big influence on human health. The major source of noise in residential areas is traffic, especially the contact between tire and pavement of road (tire/road noise). Asphalt is the most used pavement in residential areas, but cobblestones, for example, are used in historic parts of cities. There are relatively a few road surfaces with cobblestones, but with regard to noise, it is very important to monitor their acoustical behavior. Article compare the tire/road noise of the stone mastic asphalt with the maximum grain size 11 mm and cobblestones measured by the Close- Proximity method in 2021. The measurements were performed on the same road within the following sections at velocities from 30 to 90 km/h. The results are presented as values of sound pressure level and frequency spectra.

1. INTRODUCTION

Noise is a very serious pollutant affecting human health, according to the World Health Organization [1]. 140 million people in the European Union (EU) are bothered by day-evening- night noise L den (from road, rail, air traffic and industry) exceeding 55 dB. The vast majority of these (113 million) are affected by road traffic noise [2]. The annual cost of the health impacts of noise within the EU is very significant, amounting to tens of billions of euros [3]. The condition of the road surface in relation to overall road traffic noise already plays a significant role because the tire/road noise starts to domain from velocities of 20 km/h for electric vehicles, 40 km/h for passenger cars and 70 km/h for trucks, both with combustion engine [4,5].

There are several ways to influence the tire/road noise. One of them is the use of quiet tires but people's willingness to pay a higher price for quiet tires is not guaranteed. Significant speed reductions as well as diverting traffic elsewhere to reduce noise are often not optimal solutions. These solutions are often not very environmentally friendly or economical, which is often not desirable from the point of view of the national economy. The easiest thing to do on roads, even without significant public and business comment, is to influence the road surface. Regarding the long-term sustainability of transport, a favorable condition can be achieved by a high-quality road surface.

Condition of the road surface is also one of the major influencing factors in the overall result of the noise map calculation. The use of surface information is required under the new CNOSSOS-EU

1 blanka.hablovicova@cdv.cz 2 petra.markova@cdv.cz 3 vitezslav.krivanek@cdv.cz

[6] methodology. However, the surface noise values given in the methodology are the same throughout the EU. Each EU country uses mixtures adapted to local conditions. Thus, they do not match each other in terms of parameters, composition, or noise levels. So, to refine their outputs, individual countries are investigating the acoustic properties of road surfaces in their territory. These parameters will then be implemented in the calculation software required by the methodology.

Tire/road noise comparison of exposed aggregate cement concrete and stone mastic asphalt (SMA) surfaces performed by Close-Proximity (CPX) method is mentioned in the article [7]. This work is followed by the tire/road noise comparison of cobblestone and two SMA 11 surfaces presented in this paper.

2. MEASUREMENTS BY CPX METHOD

The realization of reliable repeated measurements with a time interval is a necessary condition for an evaluation of the influence of road surfaces on road traffic noise. The basic description of the CPX method is contained in the standard ISO 11819-2, which specifies the basic measurement requirements, including a speed correction for each surface type. ISO/TS 11819-3 then defines two reference tires for use in the CPX method. It also specifies the conditions for handling the reference tires, including their storage, as well as the introduction of maximum tire wear and hardness corrections, which must be within a defined interval. For this purpose, an ISO/TS 13471-1 technical specification has also been issued which sets out procedures for considering the effect of temperature on noise emissions at the tire/road interface.

2.1. Measurement conditions Meeting the acoustic conditions and ensuring the required load on the measuring tire is achieved by a specialized CPX trailer designed by CDV with dimensions of approx. 3 times 5 m (see Figure 1), which complies with the requirements of ISO 11819-2. The measurement is not dependent on the density of the surrounding traffic flow, it can be carried out at any time when meteorological conditions are met, short, long, and continuous road sections can be evaluated. To counteract unwanted reflections and sounds, the entire structure is made up of cylindrical profiles without sharp edges, without brakes and fenders, and with air suspension. The distance between the reference tire and the power unit of the trailing, oncoming or overtaking vehicle is approximately 4 m.

The Uniroyal Tigerpaw 225/60 R16 SRTT (designated P1 in ISO/TS 11819-3) was used for all measurements. It is recommended in the automotive industry (according to ASTM F2493) as a standard tire for reference tests. Measurements were taken in 2021 on a newly acquired reference tire that was placed in the right lane of the slow lane of the road. During the actual measurement, the sound pressure level at each of the six measuring microphones, the driving speed (according to GPS), the ambient air temperature and the surface temperature were continuously recorded. A camera recording of the frontal view from the measuring vehicle and the surroundings of the measuring reference tire was also taken from each measurement.

The presented results were measured at four locations, two locations with cobblestone and two with SMA 11 surface. Asphalt is the most used pavement in residential areas, cobblestone pavements are mostly used only in historic city centers in the Czech Republic. The age of the cobblestones was more than 30 years at both sites and their size was approximately 10 times 10 cm. The first location of cobblestones was on the 2 nd class road II/422 in the municipality (see Figure 1), the measurements were carried out at velocities of 30–50 km/h. The second location was on the 2 nd class road II/443 outside the municipality, the measurements were carried out at velocities of 30–90 km/h. Detailed measurement conditions are shown at Table 1. The first section of SMA 11 was located on the city bypass of the 1 st class international road I/50, the wearing course was laid in 2010 (see Figure 2). The second section was located on the 1 st class international road I/38 and laid

in 2018. Both sections of SMA 11 pavement were carried out at velocities of 30–90 km/h. Detailed measurement conditions are shown at Table 2.

Figure 1: Open CPX trailer designed by CDV located on measuring section of cobblestones II/422.

Figure 2: SMA 11 pavement on the I/50 city bypass.

3. RESULTS

The main output of the measurement is the equivalent sound pressure level L CPX:P1 and the one- octave frequency spectrum for each location according to ISO 11819-2. The A-weighting filter adapts the sound recording to the sensitivity of the human ear. The obtained data were subjected to postprocessing within PULSE LabShop. Statistical evaluation and necessary corrections (e.g., temperature, velocity) were made after exporting the measured values. The standards ISO 11819-2 specifies that tire/road noise by CPX method must be measured at least at frequencies of 315– 5,000 Hz. The measurements of presented results were performed in the frequency range 63– 8,000 Hz.

Table 1 shows the results and conditions of measurements (actual air and surface temperature, real velocity) of cobblestone pavements. The first column represents location of section and the date of measurement (yy-mm-dd). The tire/road noise was similar for both locations at lower velocities, so similar acoustic behavior can be expected at higher velocities. Noise difference between velocities decreases with increasing velocity. E.g., the difference is approx. 5 dB between velocities 30 and 40 km/h but only 2 dB between velocities 80 and 90 km/h.

Table 1: Results and measuring conditions of cobblestone pavements.

Corrected

Actual air temperature

Actual surface

Location

L CPX:P1 [dB(A)]

Real velocity

velocity

temperature

date

[km/h]

[km/h]

[°C]

[°C]

30 87.6 15.6 23.3 30.63

II/422 21-05-06

40 92.4 15.4 21.8 39.65

50 96.5 15.6 21.1 51.91

30 87.2 18.1 29.6 30.38

40 92.3 19.6 34.9 39.31

50 96.1 18.2 31.0 51.79

II/443 21-06-14

70 102.3 18.3 31.7 71.19

80 104.8 18.9 34.0 80.54

90 106.8 18.5 31.8 89.47

Figures 3 and 4 express the one-octave frequency spectra for both locations with cobblestone pavements. The noise values of L CPX:P1 are similar for velocities 30–50 km/h but the frequency spectra results are slightly different. In the frequency interval 63–500 Hz, the noise values L CPX:P1 of cobblestones from the II/443 road outside the municipality are higher. However, the differences are mostly small, within the measurement uncertainty, which is ± 1 dB. The highest noise valueswere measured at frequency 1,000 Hz for both locations and for all velocities. The II/422 road in the municipality with cobblestone pavement has a higher noise values L CPX:P1 than II/443 road for frequency interval 1,000–8,000 Hz.

100

90

L CPX:P1 [dB(A)]

80

70

60

50

10 100 1000 10000

Frequency [Hz]

30 km/h 40 km/h 50 km/h

Figure 3: Noise frequency spectra of cobblestones in location II/422 for different velocities.

100

90

L CPX:P1 [dB(A)]

80

70

60

50

10 100 1000 10000

Frequency [Hz]

30 km/h 40 km/h 50 km/h 70 km/h 80 km/h 90 km/h

Figure 4: Noise frequency spectra of cobblestones in location II/443 for different velocities.

Table 2 shows the results and conditions of measurements (actual air and surface temperature, real velocity) of SMA 11 pavements. The first column represents location of section, age of wearing course (after laying) and the date of measurement (yy-mm-dd). The results about decreasing noise differences between velocities are like cobblestones, except difference for I/38 between velocities 80 and 90 km/h which is higher than previous. The noise values of L CPX:P1 are not as similar as for cobblestone for the same velocities, differences are in range 0.7–1.7 dB. Logically, higher noise levels were measured for the older surface.

Figures 5 and 6 express the one-octave frequency spectra for both locations with asphalt pavement SMA 11. The highest noise values were measured at frequency 1,000 Hz for both locations and for all velocities. Noise increases up to frequency 1,000 Hz, then decreases. The highest noise difference 4.7 dB between locations was observed at a frequency 500 Hz at velocity

90 km/h. Very high noise difference 4.5 dB was found at a frequency of 63 Hz at velocity 40 km/h. Tire/road noise results of the SMA 11 surface correspond with the results of project ROSANNE [8]. Table 2: Results and measuring conditions of SMA 11.

Location

Corrected

Actual air temperature

Actual surface

L CPX:P1 [dB(A)]

Real velocity

(age)

velocity

temperature

[km/h]

date

[km/h]

[°C]

[°C]

30 83.9 26.2 46.0 30.88

40 89.1 25.5 44.0 40.69

I/50 (11) 21-06-23

50 92.8 25.5 45.2 49.89

70 98.0 26.0 44.0 69.02

80 100.3 26.2 43.8 78.64

90 102.1 25.4 44.4 89.22

30 83.2 22.1 34.5 30.79

40 88.2 23.7 38.2 40.80

I/38

50 91.7 23.5 39.6 51.04

(3) 21-06-10

70 96.8 23.8 41.3 69.72

80 98.6 23.5 39.1 80.84

90 100.7 23.6 40.1 89.88

100

90

L CPX:P1 [dB(A)]

80

70

60

50

10 100 1000 10000

Frequency [Hz]

30 km/h 40 km/h 50 km/h 70 km/h 80 km/h 90 km/h

Figure 5: Noise frequency spectra of SMA 11 pavement in location I/50 for different velocities.

100

90

L CPX:P1 [dB(A)]

80

70

60

50

10 100 1000 10000

Frequency [Hz]

30 km/h 40 km/h 50 km/h 70 km/h 80 km/h 90 km/h

Figure 6: Noise frequency spectra of SMA 11 pavement in location I/38 for different velocities.

Figure 7 compares one-octave frequency spectra for all measured locations at all velocities. The greatest noise differences between cobblestone and SMA 11 are achieved at lower frequencies in range 63–500 Hz. Differences higher than 10 dB were found for a frequency of 63 Hz at velocities 30 and 40 km/h; for a frequency of 125 Hz at velocities 30–50 km/h; for a frequency of 250 Hz at velocities 50–90 km/h; and for a frequency of 500 Hz at velocities 70–90 km/h, see red color in the Table 3. Tire/road noise levels of both pavements are almost the same for a frequency of 2,000 Hz at low velocities up to 50 km/h because the differences are within measurement uncertainty ±1 dB, surfaces reach very similar values at velocities 70–90 km/h with a difference of up to 2 dB.

Table 3: Difference magnitude table for velocities and frequencies – red (high difference above 10 dB), yellow (medium difference 6–10 dB), green (low difference 3–6 dB), grey (very low difference 1–3 dB), without color are similar values (difference below 1 dB).

Frequency [Hz]

Velocity

[km/h]

63 125 250 500 1,000 2,000 4,000 8,000

30

40

50

70

80

90

50 55 60 65 70 75 80 85 90 95 100 105

50 55 60 65 70 75 80 85 90 95 100 105

L CPX:P1 [dB(A)]

L CPX:P1 [dB(A)]

63 125 250 500 1000 2000 4000 8000

63 125 250 500 1000 2000 4000 8000

Frequency [Hz]

Frequency [Hz]

Velocity 30 km/h II/422 II/443 I/50 I/38

Velocity 70 km/h II/443 I/50 I/38

50 55 60 65 70 75 80 85 90 95 100 105

50 55 60 65 70 75 80 85 90 95 100 105

L CPX:P1 [dB(A)]

L CPX:P1 [dB(A)]

63 125 250 500 1000 2000 4000 8000

63 125 250 500 1000 2000 4000 8000

Frequency [Hz]

Frequency [Hz]

Velocity 40 km/h II/422 II/443 I/50 I/38

Velocity 80 km/h II/443 I/50 I/38

50 55 60 65 70 75 80 85 90 95 100 105

50 55 60 65 70 75 80 85 90 95 100 105

L CPX:P1 [dB(A)]

L CPX:P1 [dB(A)]

63 125 250 500 1000 2000 4000 8000

63 125 250 500 1000 2000 4000 8000

Frequency [Hz]

Frequency [Hz]

Velocity 50 km/h II/422 II/443 I/50 I/38

Velocity 90 km/h II/443 I/50 I/38

Figure 7: Comparison of frequency spectra for all measured locations (yellow = cobblestones, blue = SMA 11).

4. CONCLUSIONS

The tire/road noise of two cobblestone and two SMA 11 surfaces were measured by CPX method at velocities 30–90 km/h. Noise values of the older SMA 11 wearing course were higher in the whole spectrum for all velocities than younger one probably because of various deformations. In contrast, the values of cobblestone pavements were similar for both locations because they were more than 30 years old. The highest noise frequency spectrum differences between cobblestone and SMA 11 are achieved at lower frequencies in range 63–500 Hz; surfaces reach almost identical values at frequency 2,000 Hz. Generally, it can be concluded that the differences are high for lower frequencies and low for higher frequencies. Cobblestone surfaces are noisier than wearing courses with SMA 11 by approximately 4–5 dB. 5. ACKNOWLEDGEMENTS

This paper is financed from the state budget by the Technology Agency of the Czech Republic and the Ministry of Transport of the Czech Republic under the DOPRAVA2020+ Programme, project CK02000121 Determination of values of classification levels for evaluation of road surface noise in the Czech Republic. 6. REFERENCES

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