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The ReGreeneration project, led by C40 Cities and supported by ARUP, Placemaking Europe, Climato Sfera, Inetum, and many others, operates at the intersection of urban ecology, public health, infrastructure, and neighborhood-scale design. Its premise addresses how European cities are built and maintained and how they experience a changing climate, arguing that cities must fundamentally change to remain livable under accelerating climate pressures.

The European Commission launched Horizon Europe in 2021 as its most ambitious research and innovation program to date, committing over 95 billion euros to accelerate scientific discovery and address the defining challenges in European cities. Among the initiatives that Horizon Europe funds is ReGreeneration, a transnational consortium uniting nine cities, their governing bodies, leading research institutions, and technology partners in the region.

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Elevation is often framed as progress, lifting movement above the friction of the city and smoothing circulation into uninterrupted flow. Every act of lifting produces a secondary condition in its wake. Beneath flyovers, metro lines, and railway viaducts, a second ground emerges as shaded, ambiguous, and rarely planned with the same intent as what moves above. These spaces are not incidental leftovers. They are the spatial consequence of a design decision that privileges speed, clearance, and efficiency, redistributing value and visibility across the city in the process.

What lies below is not empty. It is structured, constrained, and defined by infrastructure, left without a clear role. Studies on elevated highways consistently describe these undercroft zones as residual spaces, formed when transport systems are conceived independently of the ground they pass through. An Arup report on spaces beneath viaducts notes how they often disrupt pedestrian continuity while remaining outside formal planning frameworks. Similarly, recent academic reviews of under-flyover environments highlight that these areas are rarely integrated into urban design strategies at all. The result is a peculiar condition: space that is physically present and structurally determined, but programmatically undefined.

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