# Traffic Noise Reduction Strategy in a Large City and an Analysis of Its Effect
## 3 Results and Discussion  
### Distribution of Traffic Noise Levels with Noise Barriers  
The urban traffic noise maps of Panyu District in daytime, nighttime, and day-night with noise barriers are shown in Figures 6-8, respectively. By comparing Figures 6 and A1 (see Appendix A), it is obvious that the area covered by high noise levels in the daytime was significantly reduced after the installation of the noise barriers. In particular, the total area exposed to the high noise levels (>65 dBA) was significantly reduced by 24.5 km\({}^{2}\), while the total area that complied with the noise limit was increased by 97.4 km\({}^{2}\) in the daytime. Among all of the classes of acoustic functional areas, the installation of noise barriers contributed the most to the class 2 functional area, which had an increment in the total area complying with the noise limit of up to 61.6 km\({}^{2}\). By comparing Figures 7 and A2, it can be found that, with the noise barriers implemented, the traffic noise level was obviously reduced in the nighttime as well. Similar findings were also observed in the day-night traffic noise maps, as shown in Figures 8 and A3. By applying the noise barriers, the range of SPLs in most areas decreased from 65-70 to 60-65 dBA, while a few areas decreased from 60-65 to 55-60 dBA. Nonetheless, the range of SPLs in very few areas decreased from 55-60 to 50-55 dBA. This implies that the functions of the noise barriers were more efficient in mitigating the noise in areas with a higher noise level.  
Figure 6: Daytime urban traffic noise map of Panyu District, Guangzhou City with the existence of noise barriers. \(L_{day}\) is the A-weighted equivalent noise level over the 16 h period of daytime (6:00 to 22:00).  
As shown in Table 4, the minimum and maximum noise levels in the daytime, nighttime, and day-night in Panyu District with and without noise barriers were summarized. As can be seen, the effect of the noise barriers on the maximum noise levels was more significant in the nighttime, and the maximum reduction of noise (ASPL) could reach up to \(\sim\) 10000.  
Figure 8: Day–night urban traffic noise map of Panyu District, Guangzhou City with the existence of noise barriers. \(L_{dn}\) is the A-weighted equivalent noise level over a 24 h period.  
Figure 7: Nighttime urban traffic noise map of Panyu District, Guangzhou City with the existence of noise barriers. \(L_{night}\) is the A-weighted equivalent noise level over the 8 h period of nighttime (22:00 to 6:00).  
to 6.1 dBA. Nevertheless, it is suggested that the noise barrier has little influence on the minimum noise level according to the noise mapping.  
As shown in Table 5, the minimum and maximum noise levels of the different functional areas were tabulated. It can be seen that the maximum noise levels in the residential and industrial areas were reduced the most in the nighttime (up to 5.5 dBA). This was due to the fact that higher noise barriers were purposely arranged along the roads near the residential and industrial areas. However, in the forest and warehousing areas, the reduction of noise levels was the smallest, as no noise barriers were installed along the roads near these areas.