# Study on Noise Reduction with Paving Different Low Noise Pavement Materials
## 4 Measurement Results
### Speed of the Trailer at 80 km/h  
Figure 6 shows the measurement results with CPX using the trailer at the speed of 80 km/h. For the inner lane, before the pavement maintenance, with ECA-10, the average equivalent sound pressure level of typical light vehicle tire/road surface is 116.7 dB, and that of typical heavy vehicle tire/road surface is 117.5 dB, so the tire/road noise of heavy vehicles is about 0.8 dB higher than that of light vehicles. After the pavement maintenance, both the tire/road noise of light vehicles and that of heavy vehicles have decreased. For the inner lane, with 2.5 cm PUC-10, the light vehicle tire/road noise has decreased by an average of 2.6 dB, and the heavy vehicle tire/road noise has decreased by an average of 1.1 dB. With 4.5 cm PAC-13+2.5 cm PUC-10, the light vehicle tire/road noise has decreased by an average of 2.8 dB, and the heavy vehicle tire/road noise has decreased by an average of 3.8 dB. average of 1.8 dB, and the heavy vehicle tires/road noise has decreased by an average of 0.6 dB. With 4.0 cm PAC-13, the light vehicle tires/road noise has decreased by an average of 0.7 dB, and the heavy vehicle tire/road noise has decreased by an average of 1.1 dB. For the outer lane, before the pavement maintenance, with the ECA-10, the average equivalent sound pressure level of typical light vehicle tires/road surface is 116.6 dB, and that of typical heavy vehicle tires/road surface is 117.7 dB, so the tire/road noise of heavy vehicles is about 1.1 dB higher than that of light vehicles. After the pavement maintenance, both the tire/road noise of light vehicles and that of heavy vehicles have decreased. For the outer lane, with 2.5 cm PUC-10, the light vehicle tire/road noise has decreased by an average of 2.1 dB, and the heavy vehicle tire/road noise has decreased by an average of 2.1 dB, and the heavy vehicle tire/road noise has decreased by an average of 4.1 dB. With 4.5 cm PAC-13+2.5 cm PUC-10, the light vehicle tire/road noise has decreased by an average of 2.8 dB, and the heavy vehicle tire/road noise has decreased by an average of 1.1 dB. Figure 6: Tire/road noise equivalent sound pressure level at 80 km/h before and after road maintenance (RM): inner lane (**Upper**); outer lane (**Lower**). of 4.3 dB. With 4.0 cm PAC-13, the light vehicle tire/road noise has decreased by an average of 1.1 dB, and the tire/road noise of heavy vehicles has decreased by an average of 1.7 dB. When comparing the tire/road noise measurement results of the inner lane with those of the outer lane at 80 km/h, with the ECA-10, one can see that the tire/road noise of heavy vehicles is higher than that of light vehicles. With 2.5 cm PUC-10, the average tire/road noise level of light vehicle is 114.7 dB, and the average tire/road noise level of heavy vehicle is 116.6 dB, so the tire/road noise of heavy vehicle is 1.9 dB higher than that of light vehicle. With 4.5 cm PAC-13+2.5 cm PUC-10, light vehicle average tire/road noise level is 114.1 dB, and heavy vehicle average tire/road noise level is 113.8 dB, which is very close to light vehicle tire/road noise. With 4.0 cm PAC-13, the average tire/road noise level is 115.7 dB, and the heavy vehicle average tire/road noise level is 115.8 dB. All these results are shown in Figure 7.  
From the experimental results at 80 km/h, one can also see that the tire/road noise of both the light and the heavy vehicles becomes the lowest when using the double-layer pavement, which is the same as the results in subsection 4.1. Compared with 4.0 cm PAC-13 pavement, the average tire/road noise of 2.5 cm PUC-10 is less than 1 dB for light vehicles, and higher than 0.8 dB for heavy vehicles. Therefore, at a driving speed of 80 km/h, using a combined pavement structure with a 2.5 cm PUC-10 pavement in the inner lane and a 4.0 cm PAC-13 in the outer lane, it is an alternative way to obtain a better noise reduction.