# Traffic Noise Reduction Strategy in a Large City and an Analysis of Its Effect
## 3 Results and Discussion
### Effects of Noise Barriers on the Populations of Highly Annoyed and Sleep-Disturbed Citizens  
According to the practice of [PERSON] et al. [48] and [PERSON] et al. [49], the present study calculated two group noise indicators, \"\(G_{dn}\)\" and \"\(G_{night}\)\" (dBA), for the exposed population in the University Town. These two group population noise indices, respectively, represent the nominal noise energy exposed to the population during day-night and nighttime. By combining the noise index in the present study, the group noise indices can, therefore, be calculated as follows:  
\[G_{dn} =10\cdot\log_{10}\left(\frac{1}{\mathrm{N_{tot}}}\sum_{i}^{n}n_{i} \cdot 10^{0.1\cdot L_{night,i}}\right) \tag{1}\] \[G_{night} =10\cdot\log_{10}\left(\frac{1}{\mathrm{N_{tot}}}\sum_{i}^{n}n_{i} \cdot 10^{0.1\cdot L_{night,i}}\right) \tag{2}\]  
where \(\mathrm{N_{tot}}\) is the total population, \(n_{i}\) is the population exposed to the i-th noise exposure level, \(L_{dn,i}\) is the representative value of the i-th noise exposure level in day-night, and \(L_{night,i}\) is the representative value of the i-th noise exposure level in nighttime. Referring to [48], the representative values corresponding to different noise exposure levels are presented in Table 8.  
Additionally, in order to assess the highly annoyed (\(\mathrm{P_{HA}}\)) and highly sleep-disturbed (\(\mathrm{P_{HSD}}\)) populations under the conditions with and without noise barriers, the methodologies proposed in [49; 50; 51] were applied. The calculation of \(\mathrm{P_{HA}}\) is in reference to [50], and the formula is shown below. \[\mathrm{P_{HA}}=\sum_{i}^{n}\mathrm{P_{i}}\cdot\left(9.994\cdot 10^{-4}\cdot \left(L_{dn,i}-42\right)^{3}-1.523\cdot 10^{-2}\cdot\left(L_{dn,i}-42 \right)^{2}+0.538\cdot\left(L_{dn,i}-42\right)\right)/100 \tag{3}\]  
where \(\mathrm{P_{HA}}\) is the total number of highly troubled people, and \(\mathrm{P_{i}}\) is the population exposed to the i-th noise exposure level. The calculation of \(\mathrm{P_{HSD}}\) is in reference to [49; 51], and the formula can be written as  
\[\mathrm{P_{HSD}}=\sum_{i}^{n}\mathrm{P_{i}}\cdot\left(19.4312-0.9336\cdot L_{ night,i}+0.0126\cdot\left(L_{night,i}\right)^{2}\right)/100 \tag{4}\]  
where \(\mathrm{P_{HSD}}\) is the population whose sleep is severely disturbed by traffic noises. The results of the highly annoyed and sleep-disturbed populations are summarized in Table 9. With the application of noise barriers, \(G_{dn}\) and \(G_{night}\) were reduced by 2.5 and \begin{table}
\begin{tabular}{c l c c c c} \hline \hline \multicolumn{2}{c}{**Noise Quality Level**} & **Good** & **Quite Good** & **Slightly Polluted** & **Moderately Polluted** & **Heavy Polluted** \\ \hline \multirow{3}{*}{**Day**} & Without noise barrier & 18,217 & 36,916 & 36,553 & 28,647 & 22,217 \\  & With noise barrier & 29,072 & 44,574 & 31,289 & 21,267 & 16,347 \\  & **Variation rate (\%)** & **59.9\%** & **20.74\%** & \(-\)**14.40\%** & \(-\)**28.76\%** & \(-\)**26.42\%** \\ \hline \multirow{3}{*}{**Night**} & Without noise barrier & 141 & 1862 & 20,311 & 37,951 & 82,286 \\  & With noise barrier & 160 & 3446 & 30,466 & 44,557 & 63,921 \\  & **Variation rate (\%)** & **13.48\%** & **85.07\%** & **50.00\%** & **17.41\%** & \(-\)**22.32\%** \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Population under different noise quality levels (“\(-\)” indicates a decrease). \begin{table}
\begin{tabular}{c c} \hline \hline
**Noise Exposure Level** & \(L_{dn,i}\) **(dBA)/\(L_{night,i}\) (dBA)** \\ \hline
40–45 & 43.5 \\
45–50 & 47.5 \\
50–55 & 53.5 \\
55–60 & 57.5 \\
60–65 & 63.5 \\
65–70 & 67.5 \\
77.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: The representative values corresponding to different noise exposure levels. 1.2 dBA, respectively. The smaller reduction of \(G_{night}\) could be due to the fact that the traffic flow in nighttime was relatively lighter and, hence, the effects of the noise barriers were not as significant as those in the daytime in reducing the noise energy to which the population was exposed.