# Optimized Sensors Network and Dynamical Maps for Monitoring Traffic Noise in a Large Urban Zone
## 4 Results
### Validation of Dynamap: Sites 10 and 12  
For the validation of Dynamap predictions, we have studied all the 21 measurement sites reported in Table 4. As an illustration, we discuss here only the cases of Sites 10 and 12. The former belongs to group \(g_{1}\) and the latter to \(g_{2}\). Before discussing traffic noise results, we present a comparison between traffic flow measurements, at these two locations, and the predictions from the traffic flow model (see [86] for more details on the EMTA traffic flow model). The reason for testing the traffic flow model is because it plays a prominent role in the Dynamap approach through the BTNMs, as one can see from Equation (10). The two chosen sites (10 and 12) provide examples of the difficulties that one finds in this approach (see Figure 8), and also suggest ways of improving Dynamap predictions. In Figure 8, we see the two possible behaviors typically found from our validation analysis. In Site 10 (Figure 8a), one can see that the traffic model drastically underestimates the actual traffic flow. This is because Site 10 belongs to the lowest flow group in Z9, where the model is less accurate. The latter is indeed 'tuned' to work better for high traffic flow road stretches. The model predictions for Site 12 (Figure 8b) are, in contrast, in very good \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Site** & \(g_{i}\) & \(L^{(1h)}_{\text{eq}}\) & \(s(g_{1})\) & \(s(g_{2})\) & \(s(g_{3})\) & \(s(g_{4})\) & \(s(g_{5})\) & \(s(g_{6})\) \\ \hline
1 & 5 & 64.0 & 21.7 & 44.9 & 54.3 & 55.0 & 62.7 & 37.7 \\
2 & 2 & 65.8 & 12.0 & 64.6 & 15.0 & 15.0 & 15.0 & 59.6 \\
3 & 3 & 63.6 & 0.0 & 56.1 & 62.7 & 0.0 & 0.0 & 0.0 \\
4 & 3 & 60.8 & 17.3 & 25.4 & 59.9 & 49.2 & 51.5 & 0.0 \\
5 & 5 & 68.0 & 29.7 & 25.9 & 32.3 & 29.4 & 68.0 & 33.8 \\
6 & 3 & 64.3 & 38.8 & 45.4 & 64.2 & 34.2 & 26.9 & 28.0 \\
7 & 2 & 59.2 & 24.1 & 58.1 & 51.4 & 17.8 & 42.2 & 45.6 \\
8 & 3 & 55.4 & 21.8 & 22.0 & 54.1 & 49.6 & 30.4 & 30.1 \\
9 & 5 & 62.6 & 8.5 & 32.0 & 34.7 & 43.0 & 62.5 & 0.0 \\
10 & 1 & 45.2 & 38.1 & 43.6 & 26.6 & 25.6 & 33.0 & 28.3 \\
11 & 1 & 55.5 & 55.1 & 20.8 & 32.0 & 37.8 & 43.0 & 0.0 \\
12 & 2 & 62.1 & 42.3 & 61.8 & 24.1 & 20.4 & 48.3 & 41.0 \\
13 & 4 & 68.2 & 41.2 & 53.0 & 38.2 & 68.0 & 41.2 & 38.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The calculated total reference levels (BTNM), \(L^{(1h)}_{\text{eq}}(t_{\text{ref}},s)\), at 13 arbitrarily chosen sites \(s\) of pilot Zone 9 (cf. Table 4). The level contributions from each group, \(L^{(1h)}_{\text{eq}}(t_{\text{ref}},s(g_{i}))\), are reported in columns (4 th–9 th) [86]. All levels are expressed in dB. The underscored values correspond to the largest contribution to each reference level. Here, the number 0.0 stands for vanishingly small values. agreement with the measurements. We will see below the consequences these outcomes have on the local traffic noise predictions. In Figure 9a (upper and lower parts), we compare the Dynamap predictions, Equation (10), for Sites 10 and 12 with the actual measurements. We find in both cases that the absolute noise levels, \(L_{\text{eq}}^{(1h)}(t,s)\), as a function of hour of day, depart from the measured ones essentially by a constant amount. For Site 10, the prediction underestimates the experimental values, while, for Site 12, Dynamap overestimates it. For both sites, the discrepancies are higher during the day time than during night hours. Notice also the wild variation in the statistical errors (shown as the color bands in Figure 9), as a function of hour of the day. In particular, during the day time (7:00-9:00 p.m.), the statistical error is rather small, i.e., \(\sim\)1 dB, after averaging over all sites in the group, whereas in the evening-night time (9:00 p.m.-7:00 a.m.), the error bands are much larger, i.e., \(\sim\)(2-4) dB on average, due to the high variability of traffic flow and associated noise during night hours. These considerations led us to study the presence of systematic errors inherent in the Dynamap approach.