## 5 Conclusions  
This study investigated the acoustic analysis of the Engineering School of Bologna site in Terracini Street and the design of a combined solution to mitigate the noise pollution in this area. The acoustic measurements along Terracini Street have pointed out that the LAeq values exceed the daytime (6:00 to 22:00) regulation limits by 9 dB(A). Additional control acoustic measurements performed in the noisiest hours (in terms of L\({}_{\text{Aeq}}\)) highlighted the importance of the number of vehicles on the measured noise levels (1216 vehicles/hour with an L\({}_{\text{Aeq}}\) of 62-67 dB(A) and L\({}_{\text{Amax}}\) of 80-82 dB(A)), thus proving the importance of shielding the university site from such a noise hazard. Terracini Street is part of the crucial infrastructure of this area and cannot be subjected to traffic limitations (the urban fabric has been developed constantly in the last ten years). For this reason, this present study proposed a combination of passive acoustic techniques, such as a low-noise road  
Figure 13: Rendering of the SCAB applied at the entrance of the University of Bologna, School of Engineering, from Terracini Street. The inset shows the metallic structure designed to hold the PMMA cylinders in place. pavement and a sonic crystal-based noise barrier (SCAB). Specifically, for the noise barrier, [PERSON]'s method helped define each SCAB section's height (variable from 4 to 8 m according to the specific traffic noise in the analysed sections). Due to the environmental impact of the noise barrier, attention was paid to the combined acoustic, lighting, shading, and ventilating effects, which a standard barrier could have rarely resolved. For this reason, SCABs were designed, reproducing an effective solution already reported in [3]. Finally, the insertion loss spectrum was calculated for the various sections. The project also assessed the dimensioning and verification of the static actions (loads and wind action) and the seismic action of the barrier's structural system numerically, which is to be detailed in further work. Overall, constructing a noise barrier with sonic crystals and adding a low-noise road pavement may reduce traffic noise by 10 dB(A) on average (with a maximum of up to 25 dB(A) from 600 Hz onwards), allowing compliance with the noise pollution limits from national regulations. Moreover, the semitransparent PMMA sonic crystals have a less visually impactful appearance and are more permeable to airflow, leading to better structure permeability in terms of light and ventilation and reducing the wind load considerably [3]. The rendering of the SCAB placed on the site shown in Figure 13 represents how much visual, ventilation, and acoustic permeability allow the university site to (i) be immediately recognisable from the outside and (ii) the students inside to feel properly oriented, although the input from the outdoor environment is filtered [10; 38]. This ergonomic feature can be crucial for increasing students' comfort from a more complex sensory sphere and contributes to the overall well-being of those inside the classrooms [39]. Terracini Street is a multifunctional site that has overcome several urban modifications over the last 50 years. In this study, it has been proved that a metamaterial-based noise barrier solution could significantly improve noise mitigation while not degrading the urban quality of the site (provided by the ergonomic design through shading, ventilation, and transparency effects). The method and the results shown could set a new starting point for environmental acoustic studies in multifunctional sites, and further studies could verify the broader applicability of such a method. Conceptualization, G.F. and M.G. ; methodology, G.F. and M.G. ; software, G.F.; validation, G.F. and M.G. ; formal analysis, G.F.; investigation, G.F. and M.G. ; resources, M.G. ; data curation, G.F. and M.G. ; writing--original draft preparation, G.F. and M.G. ; writing--review and editing, G.F. and M.G. ; visualization, G.F.; supervision, M.G.