# Traffic Noise Reduction Strategy in a Large City and an Analysis of Its Effect
## 4 Conclusions  
Based on a traffic noise map of Panyu District (including road and railway traffic noise), noise barriers were proposed for implementation in areas that suffer from high traffic noise levels. The effects of noise barriers on the spatial noise distributions, noise quality levels, populations exposed to traffic noise, and populations of highly annoyed and sleep-disturbed people were analyzed. Noise compliance maps with and without noise barriers were compared. The results showed that, with the application of noise barriers, the coverage of areas with better traffic noise quality levels (good, quite good, and slight pollution) increased, while the coverage of areas with worse traffic noise quality levels (moderate and heavy pollution) decreased. Furthermore, the total noise level compliance rates during the daytime and nighttime were increased by about 18.38% and 12.62%, respectively. It was found that noise barriers were quite effective in improving the quality of the sound environment of residential areas, and thus, the populations exposed to detrimental traffic noise were significantly reduced. The group noise indicators \(G_{dn}\) and \(G_{night}\) showed that the application of noise barriers could reduce the average noise energy to which the population was exposed, and thus, the population of highly annoyed people was significantly reduced. However, \(G_{night}\), which represented the population of sleep-disturbed people, indicated that the effect of noise barriers on the population of sleep-disturbed people was not as significant as that of the population under high annoyance. Nonetheless, noise barriers can still be considered as an effective noise reduction measure that can be applied in critical urban areas under high traffic noise exposure. In the present study, the noise barriers studied were traditional ones that were built in commercial software for noise mapping. In fact, these types of noise barriers cannot reflect the performance of the latest concepts of noise barriers in real applications. In the future, with the collection of the design and performance parameters of newly optimized noise barriers, such as sonic crystal noise barriers [52], sonic crystal barriers with resonator holes [53], and metamaterial noise barriers [54,55], the methodologies proposed in this study can be applied to evaluate the effects of new types of noise barriers on the qualities of the sound environments of large cities with dense populations. Conceptualization, H.M.L. ; methodology, H.M.L. ; software, W.L. and H.P.L. ; validation, W.L. ; formal analysis, W.L. ; investigation, W.L. ; resources, H.M.L. and J.X. ; data curation, W.L. ; writing--original draft preparation, H.M.L. ; writing--review and editing, H.M.L. ; visualization, H.P.L. ; supervision, H.M.L. and J.X. ; project administration, H.M.L. ; funding acquisition, H.M.L. and J.X. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China [51908142], Natural Science Foundation of Guangdong Province [2019A1515012223, 2021A1515012269], and Guangzhou Basic Research Program--City School (College) Joint Funding Project [202102010384, 202102010410]. \begin{table}
\begin{tabular}{l c c c c} \hline  & \(G_{dn}\) (dBA) & \(G_{night}\) (dBA) & \(P_{\text{HA}}\) & \(P_{\text{HSD}}\) \\ \hline
**Without noise barrier** & 69.6 & 62.1 & 26,605 & 10,559 \\
**With noise barrier** & 67.1 & 60.9 & 20,709 & 10,052 \\
**Difference** & 2.5 & 1.2 & 5896 & 507 \\ \hline \end{tabular}
\end{table} 
Table 9: \(G_{dn}\), \(G_{night}\), \(P_{\text{HA}}\), and \(P_{\text{HSD}}\) for the University Town. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Data are available from the corresponding author on request. **Conflicts of Interest:** The authors declare no conflict of interest. Figure A3: Day–night urban traffic noise map of Panyu District, Guangzhou City [36].