As cities grow and change, complex networks of elevated concrete highways and railways sprout up like vines, twist around each other and radically transform the space beneath them. Formerly vibrant urban districts are shrouded in darkness, and the potential to use that space is often wasted as officials fence it off or incorporate hostile features into the infrastructure to ward off loiterers and people lacking housing. Over time, some of those elevated roads might become obsolete, making the whole area feel like an urban wasteland.

But the need to make use of every available square foot of land is intensifying – and city planners working on the viaducts and overpasses of the future should probably take note of how that land is currently being reclaimed and rehabilitated to enhance its value to surrounding communities.

After the success of the High Line in New York City, an elevated linear park running along a former New York Central Railroad spur, many cities have begun transforming their own underpasses, viaducts, abandoned highway sections and even the tops of tunnels into verdant public spaces.

Atlanta’s BeltLine, Detroit’s Dequindre Cut and Washington D.C.’s planned 11th Street Bridge Park all demonstrate the how valuable the land can be to residents living nearby once it’s reactivated. These underpass parks can be surprisingly vibrant, like the 8-acre Underground at Ink Block park in Boston, Houston’s Sabine Promenade (top) or Toronto’s Bentway, which includes a 720-foot ice skate trail. Skate parks, like Portland’s Burnside ramps, are a natural fit.

Art installations brighten up cavernous underpass spaces, whether with colorful lights like San Antonio’s temporary Ballroom Luminoso installation by JB Public Art or with oversized sculptural elements like the flowers of Glasgow’s Phoenix Park. Some underpass spaces draw regular crowds as venues for movies or events, like Folly for a Flyover by Assemble in Hackney Wick, England.

In Yokohama, Japan, a notorious red light district flourished beneath an overpass for decades before authorities wiped out it, turning a bustling (if crime-ridden) area into a ghost town virtually overnight. A recent redevelopment project called the Koganecho Centre tucks a complex of new buildings into this underutilized space to make it functional for residents in a new way, adding an art gallery, a cafe, a meeting space, an artist’s atelier and an open-air piazza to a 328-foot stretch under the concrete arches.

Housing can take shape around and beneath viaducts, too. In 2005, Zaha Hadid completed the Spittelau Viaducts Housing Project as part of a waterside revitalization scheme in Vienna, Austria. A three-part structure of apartments, offices and artist studios winds through, around and beneath a disused railway viaduct, playfully interacting with it while creating a contrast between old and new. Even tiny slivers of land beside viaducts can avoid feeling dwarfed, darkened and constrained by the infrastructure when cleverly designed, like the narrow Archway Studios live-work space by Undercurrent Architects or the Koops Mill mixed-use development occupying a former brownfield (both in London.)

Unfortunately, even when they become magnets for pedestrians, cyclists, families and tourists, these urban revitalization projects aren’t all sunshine and rainbow bike racks. Some of them perpetuate cycles of displacement, pushing low-income and other marginalized populations further away from amenities instead of serving them. Urban infrastructure projects are often built in poorer areas of town in the first place.

Transforming empty space into parks and venues might improve them, but it might attract deeper-pocketed buyers to the area, too. The High Line, for example, is currently struggling to make up for the imbalances it has created in once-affordable areas of Manhattan’s Chelsea neighborhood. Incentivizing affordable housing developments along with all the other elements of an underpass or viaduct makeover could help build equity into these projects from the beginning phases.

Quite possibly the most filmed and photographed bridge in the world, the Sixth Street Viaduct, spanning the Los Angeles River, is a challenging icon to replace, but the Ribbon of Light aims to try.

The famous Art-Deco viaduct in question, built in 1932, has been featured in dozens of films, television shows, music videos and video games, including Grease, Gone in 60 Seconds, Terminators 2 and 3, Madonna’s ‘Borderline’ video and episodes of Lost and 24.

Some sequences show the most recognizable part (directly over the LA river) being driven across, but many are shot from the river below. Unfortunately for fans, its was deemed seismically unstable thanks to compromised concrete supports, despite its historic landmark status with the city.

Architect Michael Maltzan, responsible for its replacement, has made his design an epic ode to its iconic curves, reprising and repeating them across a much longer portion of the new structure.

The new structure features arched trusses to be illuminated at night, suspended over a series of parks and paths being developed below and alongside it. A series of staircases and ramps will allow pedestrians and bikers to move up, down and across it as well.

The architects are clearly cognizant of the landmark they are replacing, and, in a way, are preserving its visibility through these repetitive forms, which actually extend much further out on either side than the original arches.

From the architects: “The project foresees a multi-modal future for the city, one that accommodates cars, incorporates significant new bicycle connections, and also increases connectivity for pedestrians to access the viaduct, not only at its endpoints, but along the entirety of the viaduct, linking the bridge, the Los Angeles River, and future urban landscapes in a more meaningful relationship.”

“These pairs of repeated concrete arches and cable-supported roadway deck are simultaneously elegant and efficient. The design approach unifies and optimizes the architecture of the viaduct through repetition, creating a unique configuration through the repeated use of arches, roadway and pier forms: an iconic structure.”