# Statistical Pass-By for Unattended Road Traffic Noise Measurement in an Urban Environment
## 5 Results
### Testing
The far lane might have been noisier because of some bumps and because of a more reflective pavement than the one in the parking area where the microphones for the near lane were located. Moreover, the levels for all metrics at the 3 m microphone and at the monitoring station were more similar between the lanes, as they were not as affected by ground reflections as the standard microphone at 1.2 m height. As reported in Figure 5, the acquisitions with the microphone at 3 m and with the station were compared in terms of the difference between the two lanes. L\({}_{\rm{Amax}}\) was greatly different between lanes for both microphones, confirming \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Lane** & **Coefficient** & **Monitoring Station** & **Mic 1.2 m** & **Mic 3 m** \\ \hline \multirow{4}{*}{near} & \multicolumn{3}{c}{**SEL**} & \\  & \(a\pm da\) & 75.1 \(\pm\) 0.6 & 72.6 \(\pm\) 0.6 & 75.4 \(\pm\) 0.6 \\  & \(b\pm db\) & 22.8 \(\pm\) 4.5 & 22.3 \(\pm\) 4.5 & 21.6 \(\pm\) 4.5 \\  & \(a\pm da\) & 76.3 \(\pm\) 0.5 & 76.4 \(\pm\) 0.6 & 76.4 \(\pm\) 0.6 \\  & \(b\pm db\) & 18.9 \(\pm\) 5.4 & 20.5 \(\pm\) 5.4 & 20.2 \(\pm\) 5.4 \\  & \(\mathbf{L_{Aeq}}\) & & & \\ near & \(a\pm da\) & 68.7 \(\pm\) 0.6 & 67.2 \(\pm\) 0.6 & 69.6 \(\pm\) 0.3 \\  & \(b\pm db\) & 31.3 \(\pm\) 4.5 & 30.1 \(\pm\) 4.5 & 29.6 \(\pm\) 1.2 \\  & \(a\pm da\) & 69.2 \(\pm\) 0.5 & 71.3 \(\pm\) 0.5 & 70.7 \(\pm\) 0.6 \\  & \(b\pm db\) & 26.5 \(\pm\) 5.4 & 28.6 \(\pm\) 5.5 & 28.7 \(\pm\) 5.5 \\  & \(\mathbf{L_{Amax}}\) & & & \\ near & \(a\pm da\) & 72.7 \(\pm\) 0.6 & 70.9 \(\pm\) 0.6 & 73.1 \(\pm\) 0.6 \\  & \(b\pm db\) & 30.4 \(\pm\) 4.5 & 29.3 \(\pm\) 4.9 & 28.6 \(\pm\) 4.9 \\  & \(a\pm da\) & 73.3 \(\pm\) 0.5 & 75.6 \(\pm\) 0.5 & 75.3 \(\pm\) 0.6 \\  & \(b\pm db\) & 26.3 \(\pm\) 5.3 & 29.1 \(\pm\) 5.4 & 26.1 \(\pm\) 5.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results with the morning common sample acquired in T1 for light vehicles. \(a\) and \(b\) units are dB(A). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Near Lane**} & \multicolumn{3}{c}{**Far Lane**} \\ \hline Metric & \(a\pm da\) & \(b\pm db\) & \(\chi^{2}\) & \(a\pm da\) & \(b\pm db\) & \(\chi^{2}\) \\ \hline SEL & 69.5 \(\pm\) 0.4 & 19.2 \(\pm\) 4.5 & 0.42 & 68.6 \(\pm\) 0.4 & 18.0 \(\pm\) 5.6 & 0.10 \\ L\({}_{\rm{Aeq}}\) & 62.8 \(\pm\) 0.4 & 25.8 \(\pm\) 4.6 & 0.69 & 60.5 \(\pm\) 0.4 & 25.2 \(\pm\) 5.7 & 0.23 \\ L\({}_{\rm{Amax}}\) & 66.8 \(\pm\) 0.4 & 25.2 \(\pm\) 4.5 & 0.78 & 64.7 \(\pm\) 0.4 & 26.4 \(\pm\) 5.7 & 0.42 \\ \hline \end{tabular}
\end{table} 
Table 3: Coefficients of the fit of data measured in T0. \(a\) and \(b\) units are dB(A). that L\({}_{\rm{Amax}}\) is more sensitive to local bumps than other indicators and is highly dependent on microphone position. Thus, the L\({}_{\rm{Amax}}\) was discarded for its sensitivity to local issues. L\({}_{\rm{Aeq}}\) difference highly depends on microphone position due to the duration of the event, which can vary significantly with the sight angle. As expected, the SEL difference was similar at both microphones. SEL, as from Equation (1), can also be used to estimate the annual averaged A-weighted equivalent sound levels L\({}_{\rm{Aeq}}\) from the annual averaged traffic flow, as explained in Equation (2). This represents an additional advantage that should drive the sound pass-by methodology to be optimized for this indicator. On the other hand, SEL depends on time interval above 10 dB(A), while L\({}_{\rm{Aeq}}\) is not corrected by the time length of the passage. Thus, as well as being corrected by the distance, the two lanes were differently influenced by the time length for the L\({}_{\rm{Aeq}}\) indicator. The greater difference with this indicator resides in the directivity of the source and the geometry of the measurement setup; as the acquisition was next to the source, a shorter time interval was needed to identify a 10 dB(A) cut compared to an acquisition at a greater height from the ground.