# Statistical Pass-By for Unattended Road Traffic Noise Measurement in an Urban Environment
## 3 Materials and Methods
### Testing  
The work started with a preliminary analysis of previously gathered data, performed in order to verify the applicability of the main idea. The dataset was retrieved from a noise measurement campaign carried out in SR 439 (Capannori, LU, Italy) for the monitoring of a one-year-old low-noise pavement (ISO 10844 optimized texture, commonly used by the Tuscany region in its road action plan). In this case, the acquisitions were originally performed with a noise monitoring station at the roadside, 10 m from the center lane, in order to verify law requirements in terms of ante- vs. post-operand noise levels. As these data were not acquired ad hoc, a preliminary procedure was applied in order to link night traffic acquired passages with noise levels acquired with a short time interval (50 ms). The pass-by events were identified, and those surpassing the background noise by at least 10 dB(A) in the noise time history were selected. According to vehicle length, categories were established, setting appropriate thresholds for two wheelers and light and heavy vehicles. This preliminary test was intended to verify the feasibility of deriving a model predicting the noise emitted by categories of vehicles by means of fits for speed vs. the different noise metrics (SEL, L\({}_{\text{Amax}}\), L\({}_{\text{Aeq}}\)) of a single vehicle passing in front of the measurement station. Distances from the monitoring station to the center lanes were known, and data were corrected for distance using a linear divergence model [37; 40] in order to enable comparison with the standard requirements (1.2 m height, 7.5 m distant from center lane). Such a technique is valuable for a comparison at different sites and can provide indexes that are comparable with standard ones. A linear correction is mandatory to compare techniques, i.e., the single moving vehicle passing by has to be represented as a linear source, and divergence rules are applied, as in Equation (2). \[NM=NM_{meas}+10\log\frac{\sqrt{d^{2}+4^{2}}}{\sqrt{7.5^{2}+1.2^{2}}} \tag{2}\]  
where \(NM\) is the selected noise metrics. Once the feasibility was achieved, a procedure was then established for acquiring data. A comparative analysis with the standard method was also performed in order to:  
* Define which sound level metric should be fitted with speed (SEL, L\({}_{\text{Amax}}\), L\({}_{\text{eq}}\));
* Verify if categorization with a traffic counter is comparable with a man-made one or if, at least, outliers are not relevant;
* Verify the influence of microphone height and position on the results' quality and the ability of the instrumentation to detect both lanes. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Step** & **Code** & **Site** & **Methods** & **Measurement Conditions** & **Results** \\ \hline \multirow{2}{*}{Testing} & \multirow{2}{*}{T0} & SR 439 & \multirow{2}{*}{U-SPB} & Extra urban road, low-noise surface, & \multirow{2}{*}{Feasibility confirmed} \\  & & Capannori (LU) & & data previously acquired & \\ \multirow{2}{*}{Testing} & \multirow{2}{*}{T1} & SP 224 & U-SPB, & Urban road, worked surface, data & \multirow{2}{*}{Calculated parameter} \\  & & Marina di Pisa (PI) & SPB-L & acquired at roadside day and night, & & chosen and comparison \\ \multirow{2}{*}{Validation} & \multirow{2}{*}{V} & Viale Togliatti Sesto & U-SPB, & \multirow{2}{*}{Urban road, low-noise surface, full} & \multirow{2}{*}{Validation completed} \\  & & Fiorentino (FI) & SPB-L & & measurement protocol applied & \\ \multirow{2}{*}{Application} & \multirow{2}{*}{A} & SR 439 & \multirow{2}{*}{U-SPB} & Extra urban road, & \multirow{2}{*}{Surface evaluated} \\  & & Massaroas (LU) & & & ante-/post-operand measurements & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of measurement campaigns. A simple, straight road with free field conditions and a standard pavement (dense asphalt concrete) was selected for this phase. The site was chosen for the performance of both standard SPB and U-SPB in a short time.