Highway natural borderscapes. The landscape potential of infrastructural residual spaces in the case of Milan ring roads

Highways, considered the main protagonist of urbanization and accessibility, inadvertently create unique ecological niches along their edges. This contribution explores the “Highway Natural Borderscape” concept as dynamic landscapes that foster mitigation, compensation, and biodiversity-sensitive approaches along mobility infrastructures. Unlike traditional approaches to landscape design, which prioritize planned ecosystems, mobility border territories often emerge as unintentional reservoirs of flora and fauna, generated from a normative and safety imposition and later adapted to the challenging conditions imposed by the adjacent transportation infrastructure. Through an interdisciplinary lens, this research investigates the ecological dynamics of such borderscape, considering the dichotomy between spontaneous and designed planning of such landscapes, focusing on the territories crossed by the Milanese Ring Roads system. The study also addresses the implications for landscape architecture and urban planning, suggesting innovative approaches to integrate them into broader urban green infrastructure intervention / projects, particularly on the spaces of the reliquati (a term from Italian regulation that refers to a residual space along mobility infrastructures, owned by the road concessionaire but not used for mobility or other functions) and the urban voids of mobility infrastructures. By acknowledging and enhancing biodiversity within these overlooked and underused spaces, planners can contribute to the resilience and sustainability of urban environments. The proposal advocates for a paradigm shift in perceiving highways as linear infrastructure and dynamic corridors that, when properly managed, can support broader green infrastructures by enhancing the value of such neglected residual spaces. Recognizing their ecological potential opens new avenues for sustainable urban development, emphasizing the importance of embracing and optimizing the unintended environmental consequences of human infrastructure.