# The Effects of Signal System and Traffic Flow on the Sound Level
## 3 Results and Discussion
The distance correction is given by \(20\log_{10}\left(\frac{r_{h}}{r_{1}}\right)\), where \(r_{1}\) and \(r_{h}\) are the distances of the 1 st and \(h\)th vehicles from the measurement location, respectively. Figure 6: A comparison of average sound pressure levels under “stop and go” traffic scenarios. (**a**) Van, turn; (**b**) Van, straight; (**c**) Coach, straight. Figure 7: A comparison of average sound pressure levels (\(L_{10}\)) against the stop durations. (**a**) Stop and go, turn; (**b**) Stop and go, straight. Figure 8: _Cont._  
When there is no vehicle, the measured sound level is considered as the background sound level (i.e., \(L_{\alpha(18),B}(t_{k})\) where \(t_{k}\) is the \(k\)th time step for no vehicle scenario). Hence, the \(L_{10}\) sound level of \(N\) vehicles for a scenario (e.g., no vehicle, deceleration, stop and acceleration case) is the noise level that is exceeded for 10% of the total time duration of the background, deceleration, stop, and acceleration scenario (i.e., \(\Delta t_{B}+\Delta t_{D}+\Delta t_{S}+\Delta t_{A}\)). The curve shapes of Figure 8a,b in the \"stop and go, turn\" cases and \"stop and go, straight\" cases are similar. Generally, the sound levels are monotonically increasing with the number of vans. When the number of vans is small, the curve slopes are deeper; and the maximum differences between the curves are also smaller. It is noted that when the number of vans is large, the dashed curve in these  
Figure 4:0 A comparison of average sound pressure levels (\(L_{10}\)) against the number of vans/coaches in “stop and go” and “non-stop” cases. (**a**) Van, stop and go, turn; (**b**) Van, stop and go, straight; (**c**) Coach, stop and go, straight; (**d**) Van, non-stop, turn; (**e**) Van, non-stop, straight; (**f**) Coach, non-stop, straight; (**g**) Cumulative frequency, van, stop and go, turn; (**h**) Cumulative frequency, van, non-stop, turn. figures, which represents the sound levels within the stop durations, are higher than the other curves. In Figure 8c, the curves are quite different from those in Figure 8a,b. The maximum sound level of the controlled coach is about 16 dB higher than that of the controlled van. The sound level of stop time = 60 s is quite constant for the entire range. The sound levels of stop times = 40 s and 60 s are very close for the number of coaches less than 14. Besides, the sound levels of stop times =20 s and 40 s start to decrease at the numbers of coaches = 8 and 16, respectively. The sound level of stop time = 20 s is minimum at the number of coaches = 14 and starts to increase. From the results in the coach cases, it is seen that the stop time plays an important role to affect the sound level. Figure 8d,e shows the sound levels in the nonstop cases of the controlled van \"going straight\" and \"turning\". The main difference is that when the number of vans is small the curves in Figure 8d are largely different from each other, while the two curves in Figure 8e are also identical (except a detectable difference at the number of vans = 4). In Figure 8f, the three curves are quite similar. They are decreasing when the number of coaches is small and start to increase at the number of coaches = 8. It is noted that a _L10_ value is the sound level just exceeded for 10% of the time. Hence, in many cases of Figure 8d-f, the _L10_ values are identical because the sound levels exceeded for 10% of the time are also identical (even though the _LAeq_ values are different). Figure 8g,h show the cumulative percentages plotted against the sound levels for the \"stop & go\" case and \"non-stop\" case. In each of these two figures, the \(x\) coordinate of the intercept pointed between the dashed line and any of other three curves represent the _L10_ of the case. In Figure 8g, each of the curves contains three portions. The slopes of the 1 st and 3 rd portions are more shallow than that of the 2 nd portion. It is implied that the sound level data can be divided into three groups.