## Materials and Methods
### Theoretical Method
#### 2.3.3 Global Sound Pressure Level Estimation
\[\Delta fi=f_{2,i}-f_{1,i}=\sqrt[3]{2}f_{1,i}-f_{1,i}\ \,\]4 _IL_ map at 1500 Hz in the ‘car’ location. Barrier with the ‘Y–Y’ cap and 3 m height. The following figures show the A-weighted sound pressure spectrum level in each 1 Hz band at the receiving positions for the selected Y-shaped double cap (including the ground reflection). Specifically, Figures 25 and 26 show the car scenarios ('Car-Person' and 'Car-Balcony' configurations, respectively) and Figures 24 and 25 illustrate the results for the ambulance scenarios ('Ambulance-Person and 'Ambulance-Balcony' configurations, respectively). These results were compared with those recorded for scenarios where conventional screen barriers (without caps) and Y-shaped double caps were used without considering the ground reflection on the barrier source side. As can be observed in Figure 25, the SPL spectrum was significantly lower across the whole frequency range under analysis in the 'Car-Person' configuration when a Y-shaped double cap was added to the barrier compared to when plain screen barriers without caps were used in the same scenario. When a comparison was made under the conditions of the 'Car-Balcony' configuration (Figure 26) between the use of Y-shaped double caps and a single screen, the improvement in terms of _IL_ when Y-shaped double caps were used is clear, although not as significant as in the 'Car-Person' configuration. Finally, the impact of canceling out the ground reflection on the SPL is that fluctuations in SPL are removed throughout the whole frequency band. Similarly, as can be observed in Figure 27, again, the highest SPL reduction in the 'Ambulance-Person' configuration as achieved when the Y-shaped double cap was used (with ground reflection). However, this was not that clear from the results recorded for the 'Ambulance-Balcony' configuration (Figure 28) since, as mentioned before, a LoS exists in this case and the influence of the modeling of the caps thus has less of an impact. Once more, the removal of the ground reflection leads to smoothed curves in the pressure levels, but with a similar evolution with respect to the cases with reflections. \[\Delta fi=f_{2,i}-f_{1,i}=\sqrt[3]{2}f_{1,i}-f_{1,i}\ \,\]5 A-weighted sound pressure level (SPL) spectrum in 1 Hz bands in Configuration 2 (Car–Balcony) for the 'YY’ cap with and without ground reflection. The screen barrier SPL spectrum is shown as a reference. \[\Delta fi=f_{2,i}-f_{1,i}=\sqrt[3]{2}f_{1,i}-f_{1,i}\ \,\]6 A-weighted SPL spectrum with 1 Hz resolution in Configuration 1 (Car–Person) for ’YY’ cap with and without ground reflection. The screen barrier SPL spectrum is shown as a reference. Finally, following Equation (32), the global A-weighted sound pressure spectrum levels (considering the whole frequency band) at the receiver locations (LdBArx) were numerically estimated, presented, and compared (Table 1) across the following scenarios: in the absence of a noise barrier; in the presence of a plain screen without a cap; in the presence of a plain screen with Y-shaped double caps; and in the presence of a plain screen with Y-shaped double caps without ground reflection at the source side of the barrier. As can be seen in Table 1, the global A-weighted SPL for road traffic in the 'Car-Person' configuration when Y-shaped double caps were used was within the safe levels with an equivalent SPL well below the threshold of 55 dB(A), which is considered by the WHO to be the level at which \"serious annoyance, daytime and evening, for outdoor living areas\" occur. Furthermore, there was an additional attenuation of about 14 dB in the 'Car-Person' and 'Ambulance-Person' configurations and 6 dB in the 'Car-Balcony' configuration when compared with plain screen barriers without caps