## 4 Discussion  
Tyre/road contact noise is directly dependent on the condition of the road surface, which is significantly affected over time by atmospheric agents, (non)performance of road maintenance, etc. [69]. The initial noise level depends primarily on the surface type, i.e., the chosen mixture, technology and precision [70]. With the gradual modernisation of the D1 motorway between Prague and Brno, acoustic changes between asphalt (SMA 11S) and concrete (EACC 8) road surface can be monitored. This makes it possible to give partial interim evidence for officials which  
Figure 11: Frequency spectra of tyre/road noise for SMA 11S and EACC 8 in years 1 and 6 after laying. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No. of Section** & **1** & **2** & **3** & **4** & **5** \\ \hline Correlation & 0.9955 & 0.9666 & 0.9803 & 0.9709 & 0.9797 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of acoustical aging of SMA 11S and EACC 8 surfaces on selected five sections. believe that the EACC 8 surface has worse acoustic properties than asphalt surface. These assumptions are based on previous experience with the transverse timing method because the noise levels measured on the original sections (surface with transverse timing) of the motorway ranged between 100 and 105 dB(A), depending on their condition. The results presented in this paper show that the average noise values of the SMA 11S and EACC 8 surfaces within the same conditions are virtually identical. Researchers in Poland came to the same conclusion, although using the SPB method [61; 71]. On the contrary, Canadians [70] claim that the asphalt wearing courses have better acoustic properties than concrete pavements with respect to the aging. This may be due to the composition of the mixtures and different climatic conditions. Another indisputable advantage of cement concrete surfaces over asphalt surfaces is their durability and long service life. According to long-term experience in the Czech Republic, on average, service life of cement concrete surfaces ranges between 20 and 30 years; for asphalt surfaces it is half this time. According to [PERSON] et al. [72], due to the sensitivity of asphalt to static and impact loads, cement concrete surfaces are more suitable for roads with high traffic such as the D1 motorway. However, if it is necessary to use SMA wearing course (e.g., on bridges), [PERSON] et al. [47] recommend using SMA 11 rather than SMA 16 for high-speed roads. In Australia, researchers also confirmed that, at the speed of 100 km\(\cdot\)h\({}^{-1}\), the SMA surface with lower grain size emits less noise than mixtures with higher grain size [73]. For both surface types used on the modernised sections of the D1 motorway, the noise level gradually increases with the increasing age and use of the road, as was expected [74]. Unless the road is significantly damaged by cracks, potholes, vertical displacement of cement concrete slabs, the occurrence of ruts on asphalt surfaces, etc., the most significant increase in noise levels on the D1 motorway occurs during the first three and four years after the construction for the EACC 8 and SMA 11S surfaces, respectively, as is evident from Figure 12.  
In the Czech Republic, the benchmark sound pressure level for CPX measurements, using P1 type according to ISO 11819-3 and at the vehicle speed of 80 km\(\cdot\)h\({}^{-1}\), is set at 98 dB(A) [75]. Both measured surfaces reach this noise level within the first year of their service life. In Germany, EACC is used as the only low-noise cement concrete surface that reduces noise by 2 dB(A) compared to the German reference surface [76]. The median EACC noise value in Germany is around 97.4 dB(A) [77]. On the D1 motorway, EACC noise level reaches median value of 97.5 dB(A) for year zero, i.e., shortly after the construction. Figure 12: Comparison of the noise levels development of the EACC 8 and SMA 11S surfaces on the monitored motorway sections.