# The Effects of Signal System and Traffic Flow on the Sound Level
## 3 Results and Discussion  
A comparison of the average sound pressure levels is presented in Figure 6a-c. These figures show the average sound pressure levels \(LA_{eq}\) plotted against the measurement time for various van speeds and coach speeds in two non-stop cases (i.e., non-stop with turning movement and non-stop with straight going movement). The average sound pressure levels \(LA_{eq}\) are calculated from the following equation:  
\[LA_{eq}=10\log_{10}\left[\frac{\sum_{i=1}^{n}10^{\frac{LA_{eq}}{10}}}{n}\right] \tag{1}\]  
where \(n\) is the number of trials in the corresponding scenarios, and \(LA_{eq}\) is the measured \(LA_{eq}\) value in the \(i\)th trial. Note that in each measurement case, there were at least three trials. In addition, the overall sound pressure levels \(LA_{eq(1s)}\) from six individual microphones at the measurement points (see Figure 3) are obtained as follows:  
\[LA_{eq(1s)}=10\log_{10}\left[\frac{\sum_{i=1}^{6}10^{\frac{LA_{eq}}{10}}}{6}\right] \tag{2}\]  
where \(LA_{eqj}\) is the \(LA_{eq}\) value recorded by each microphone at a particular time. \(LA_{eq(1s)}\) is the equivalent sound level within 1 s. \begin{table}
\begin{tabular}{c c} \hline \hline
**Number of Sound Level Meters** & **6** \\ \hline Number of measurement locations & 4 (i.e., A, B, C, D in Figure 2) \\ \hline Measurement heights & 1.2 m, 4.0 m and 6.5 m \\ \hline Vehicle type & Van and coach \\ \hline Vehicle speed & 30, 50, and 70 km/h \\ \hline Measurement scenarios & “non-stop” and “stop and go” \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the measurement information. Figure 4: Noise level variation of “stop and go” situation of a single vehicle. The average background sound levels in both van and coach cases were 55.2 dB(A) and 51.8 dB(A), respectively. The total durations of the controlled van and coach across the measurement points ranged from about 20 to 45 s. In these cases, the peak sound pressure levels of the vehicle speed at 50 km/h are 68.5 dB(A) (i.e., the non-stop and turning movement case in Figure 5a), 66.4 dB(A) (i.e., the non-stop and straight movement case in Figure 5b), and 74.6 dB(A) (i.e., the non-stop and straight movement case in Figure 5c), respectively. The controlled van took a longer time to make a turning movement to pass through the measurement points and induced a higher peak sound level at the same speed. The comparison between the van and coach cases shows that the peak sound levels of the coach at the speed of 50 km/h and 70 km/h are about 6 to 7 dB higher than those in the van cases. The coach and its engine are bigger, and thus the measurement point would be exposed to a higher sound level. Generally, it is found that the higher the van/coach speed is, the higher the peak sound level is measured. Figure 5: A comparison of average sound pressure levels under “non-stop” traffic scenarios. (**a**) Van, turn; (**b**) Van, straight; (**c**) Coach, straight. Figure 6a-c show the average sound pressure levels (\(LA_{\text{eq}}\)) plotted against the measurement time in the \"stop and go\" cases. The yellow dash line in each figure represents the background noise. There is no difference between the deceleration and stop durations in Figure 6a,b. In the acceleration durations, the peak on the sound level curve in the \"straight\" case is wider and jumps down sharply after about 10 s. Relatively, the peak on the sound level curve in the \"turn\" case is small. The sound level drops mildly after about 15 s. In the \"turn\" case, the controlled van took a longer time to make a turning movement and thus, the sound level in the acceleration duration in Figure 6a takes longer to decay sharply. In Figure 6c, the sound levels of the coach in the deceleration, stop and acceleration durations are significantly higher than those in Figure 6a,b. In the deceleration portion, there is a peak on the sound level curve (no peaks are found in the van cases).