When a Highway Becomes a Forest, Something Has Changed
In 1970, the Seoul Station Overpass was built to move cars. It was a practical structure — concrete and steel, sixteen meters above street level, functional in the way that mid-century urban infrastructure tends to be functional: efficient, large, and largely indifferent to the people walking beneath it. By 2015, the overpass had been declared unsafe for vehicle traffic and closed. The city faced a decision that urban planners in many cities have faced: demolish the structure, or find it a new purpose. Seoul chose to turn it into a forest. Not a metaphorical forest. A literal one — 645 circular concrete pots arranged along a kilometer of elevated walkway, planted with 24,000 individual specimens representing 228 species and sub-species of Korean flora, organized alphabetically by family name in the Korean script, from east to west along the length of the sup. The result, which opened in May 2017 under the name Seoullo 7017, is one of the most deliberate urban design statements any city has produced in the past decade.
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| 645 circular pots, 228 species, 17 meters above the street — Seoullo 7017 is a highway rewritten as a living alphabet. |
Seoullo is a compressed name. In Korean it means both "toward Seoul" and "Seoul street," and the 7017 encodes the overpass's timeline — 1970, the year of its construction; 2017, the year of its transformation; 17, the number of connected walkways branching from its main length; and 17 meters, its elevation above the street. Nothing about this naming is accidental. The project understood from the start that it was not just redesigning infrastructure — it was rewriting the meaning of a piece of the city, and the name needed to hold that history without erasing it.
645 Pots and the Logic Behind Each One
The design was commissioned from MVRDV, the Dutch architectural firm, which won the competition in 2015. The central challenge was structural: the original overpass was not built to support the weight of mature trees in soil beds. The solution was the pot system — individual circular planters of varying sizes and heights, distributed across the walkway surface so that the load is spread across the existing structure rather than concentrated in continuous planting beds. The pots are not a compromise. They become the visual identity of the project, their repetition and variation producing a rhythm along the gil that reads differently at different speeds — a particular geometry at walking pace, a different pattern from above, a changing silhouette as the plants inside them grow toward their eventual full heights over the coming decade.
The botanical organization of the pots is one of the more unusual decisions in the design. Plant families are arranged according to the Korean alphabet, Hangul, moving from east to west across the length of the walkway. This means that a visitor walking the full length of Seoullo 7017 is also walking, without necessarily knowing it, through a living index of Korean native flora arranged in alphabetical order. MVRDV founder Winy Maas described it as "a walkable plant library" — an educational arboretum that is also a public park, a pedestrian route, and an urban regeneration project simultaneously. The seasonal variation reinforces this: maple families provide autumn color, cherry and rhododendron bloom in spring, conifers hold their green through winter, and fruit-bearing plants mark summer. The sup changes with the calendar in ways that a conventional park, with its fixed planting, often does not.
Seoul's Longer Green Ambition
Seoullo 7017 is the most visible expression of a larger shift in how Seoul thinks about nature within its urban boundaries. In 1975, the city had 5.73 square meters of green space per person. By 2023, that figure had reached 18.74 square meters per capita — a threefold increase achieved through a sustained series of policy decisions that treated green infrastructure not as amenity but as essential urban function. The restoration of Cheonggyecheon Stream in 2003 — removing an elevated expressway that had covered the creek since the 1960s and restoring the waterway at street level through central Seoul — was the project that most visibly signaled this shift in thinking. Seoullo 7017 followed the same logic: existing infrastructure that served cars was given a new identity that served people and plants.
The Garden City Seoul policy, announced in 2023 and put into action in 2024, extends this further. The plan includes the creation of 1,007 new gardens across the city by 2026, the development of a 2,063-kilometer green path network connecting parks, forests, and waterways, and the conversion of sections of major roads — including stretches of Yeongdong-daero and Gyeongbu Expressway — into green corridors. Seoul declared itself a "Green City" in 2013, and its subsequent administrations have built on that declaration in concrete ways. The paradigm shift, as one municipal policy document describes it, was from "park as isolated destination" to "park city" — a model in which green space is embedded into streets, alleys, rooftops, and even building walls rather than confined to designated recreational zones.
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| The pots are not a compromise — they are the visual identity of a project that was always about time as much as space. |
The Urban Nursery Concept
One of the more forward-looking aspects of Seoullo 7017's design is its intended function as an urban nursery. The plants on the overpass are not simply ornamental. As trees grow beyond the capacity of their pots, they are intended to be transplanted to other districts of the city — the walkway functioning as a propagation site for Seoul's broader greening program. The circular pots include mobile versions sized for seeds and seedlings that can be transferred when ready. In this sense, Seoullo 7017 is not a finished project but an ongoing process — a linear growing space that produces its output for the wider city rather than simply displaying it in situ.
The 16 small pavilions distributed along the walkway support a range of activators: cafes, small shops, an information center, an outdoor stage, a foot bath, exhibition spaces. At night, blue lighting surrounds the planters, creating a visual counterpoint to the yellow-toned street lighting of the city below — a color chosen specifically because it is considered less disruptive to plant life than warmer artificial light. The lighting can shift in color for festivals and seasonal events. The walkway is connected to its surrounding urban fabric through a network of stairs, lifts, and escalators that link it to hotels, commercial buildings, and street-level neighborhoods — making Seoullo 7017 a connector as well as a destination, improving pedestrian circulation through the Seoul Station district in ways that benefit commuters as much as visitors.
The High Line Comparison, and Where It Falls Short
The comparison to New York's High Line is inevitable and has been made repeatedly since the project opened. Both are elevated linear parks built on repurposed infrastructure. Both have become major attractions and catalysts for surrounding urban development. But the comparison obscures some meaningful differences. The High Line was built on a decommissioned freight railway in a neighborhood that was already gentrifying rapidly when the project opened, and it has since been criticized for accelerating that gentrification in ways that displaced existing residents and businesses. Seoullo 7017 sits adjacent to Seoul Station, in a district that serves working commuters as much as leisure visitors, in a city with a broader and more systematic green infrastructure policy behind it. The walkway is not a standalone intervention but one node in a planned network.
The botanical concept also distinguishes it clearly. The High Line's planting is landscape design — beautiful, thoughtfully arranged, and decidedly aesthetic in its primary ambition. Seoullo 7017's planting is taxonomic. It is organized as knowledge as much as experience, a living reference organized by the same alphabetical logic you would use to look something up in a book. Walking through it, you can read the labels on the pots and learn what you are looking at. The sup is not just something to look at. It is something to be read.
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| At night the planters glow in blue — a color chosen because it is kinder to the plants than the yellow light of the city below. |
What a City Chooses to Grow
The decision to plant 228 species of specifically Korean native flora on a former car overpass in the center of Seoul carries a cultural dimension that goes beyond urban greening. The species were selected to represent what grows naturally in and around Korea — not the ornamental plants that dominate most urban landscaping, but the trees, shrubs, and flowers that constitute the country's ecological heritage. Bringing them into the city center, labeling them in Hangul, organizing them as an accessible public dictionary — this is an act of cultural as well as botanical preservation.
Seoul's population has lived through one of the most dramatic urbanization processes of the twentieth century, moving from a predominantly rural society to a city of ten million people in less than two generations. The sup of Seoullo 7017 is, among other things, a response to that speed — an attempt to reintroduce, at the center of the most urban part of the city, the specific plant life that urbanization pushed to the periphery. Whether a circular concrete pot on a steel overpass is an adequate substitute for an actual forest is a question the project does not fully answer. But the question it does answer — whether a city can choose to grow things upward when it has run out of ground — Seoul has resolved clearly in the affirmative.
If a city is what its infrastructure says it values, what does it mean when a highway becomes a forest?
Continue your journey into Korean life below:
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