## 1 Introduction  
Over the past decades, the rise in the development of new infrastructures has led to an increased concern regarding environmental noise in expanding urban areas [1]. This matter has been investigated using various methodologies across multiple scientific disciplines, including urban engineering, environmental engineering, acoustics, soundscape, landscape architecture, economics, sociology, ecology, and anthropology [2; 3; 4]. Many of these approaches start by analysing the historical context and the physical and structural characteristics of the area under study. Furthermore, most of these methods incorporate regulatory aspects into evaluating the expanding site, encompassing acoustic, urban, and infrastructural regulations at the local, national, or international levels [5; 6]. These studies often comprise a design phase implying the local community's and stakeholders' active involvement [5; 7]. Participatory tools such as focus groups, questionnaires, and sound walks facilitate this engagement [8; 9]. After gathering the environmental condition evolution and the evolving area's public opinion, several noise-reducing measures can be exploited to solve targeted environmental acoustic problems, like low-noise road pavements, noise barriers, regulatory car speed reduction, and viability modification [3; 10; 11; 12; 13; 14; 15]. Moreover, targeted solutions (like sound-proofing windows or louvres) can be developed for buildings where acoustic comfort is critical for indoor activities, such as schools, hospitals, or offices [16].  
Specifically, noise barriers can be helpful when the infrastructure is very close to the occupied public area [10]. They are one of the most effective means of noise reduction and,in fact, are frequently used for road traffic and train noise. Noise barriers can be made of sustainable materials [17] and characterised in situ [18]. Moreover, nowadays, there are new assessment methods to validate innovative noise barrier solutions [18; 19]. However, noise barriers can be visually impacting and ecologically disruptive, so new design concepts should be outlined using, for example, metamaterials [3]. Metamaterials are a versatile solution to acoustic and multidomain problems. They can be tuned to several frequency ranges for sound absorption and insulation, and in some contexts, they can simultaneously allow air passage and noise attenuation [3; 4].  
This study aims to (i) assess the environmental acoustic conditions of Terracini Street due to the increasing traffic within a multipurpose area and (ii) define an innovative solution for screening the university campus area, which is particularly sensitive to noise pollution. Therefore, first, Terracini Street's urban evolution within the Navile district was investigated by considering the morphological characteristics, urban function, and noise limits. Secondly, environmental acoustic measurements were performed to assess the actual condition of the area under investigation, and it was found that the noise limits were exceeded. Finally, sonic crystal noise barriers were designed to screen the public university area from traffic noise while trying not to significantly modify the pedestrian viability, architectural barriers to road traffic, and emergency exits. Since the site has a social meaning for the students, particular attention was paid to the visual and ecological impacts of the noise barrier. The sonic crystal technique was exploited for an effective noise barrier on a broad frequency range, simultaneously allowing air ventilation and visual transparency. This case study could further evolve using other acoustic metamaterial techniques or in different application sites.