Oh Se-hoon Announces "Gangbuk Transverse Underground Expressway Plan"
Undergrounding and Demolition of Elevated Section from Seongsan IC to Sinnae IC
Second Phase: Considering Undergrounding from Hawolgok to Seongdong
Estimated Cost: 3.4 Trillion
The Seoul Metropolitan Government will underground a 20.5-kilometer section of the Inner Ring Road and Bukbu Expressway, stretching from Seongsan Interchange (IC) to Sinnae Interchange (IC), by 2037. A six-lane, bidirectional underground road will be constructed, and the existing elevated roads will be demolished after the new route opens. The project is expected to cost 3.4 trillion won, and the city aims to enhance the competitiveness of the Gangbuk area by eliminating the two major arterial roads that have caused urban fragmentation.
On the morning of December 18, Seoul Mayor Oh Se-hoon announced the "Gangbuk Transverse Underground City Expressway Construction Plan" at Seoul City Hall, stating, "We will return leisure spaces to citizens by undergrounding the Inner Ring Road and Bukbu Expressway."
Section of the "Gangbuk Transverse Underground City Expressway Construction Plan" project unveiled by Seoul Mayor Oh Se-hoon on the morning of the 18th. Seoul City
The core of the project is to demolish a total of 20.5 kilometers, including the section of the Inner Ring Road from the Seongsan Bridge area (Seongsan IC) to Gilum IC, and the section of the Bukbu Expressway from Gilum IC to Sinnae IC in Sinnae-dong.
Instead, a six-lane, bidirectional underground expressway will be built. Taking into account that one or two additional lanes will be created on the ground level where the elevated roads are removed, the Inner Ring Road will expand from the current 12 lanes (six elevated + six surface) to 14 lanes (six underground + eight surface), while the Bukbu Expressway will increase from the current 10 lanes (four elevated + six surface) to up to 14 lanes (six underground + eight surface).
The project cost is estimated at 3.4 trillion won, which includes the construction of the underground city expressway, demolition of existing elevated roads, and improvements to surface roads. However, this is a provisional figure at the project planning stage. The city plans to further refine the project scope and implementation methods after comprehensively reviewing future traffic demand forecasts, congestion mitigation effects, and fiscal conditions.
During the project, the city will also consider undergrounding the remaining 6.5-kilometer "Hawolgok-Seongdong section" of the Inner Ring Road, taking into account traffic conditions, surrounding area circumstances, and the city's financial situation. This would effectively mean the entire Inner Ring Road would be moved underground.
Mayor Oh expects that undergrounding the Inner Ring Road and Bukbu Expressway will significantly improve both regional connectivity and residential conditions in the area. On this day, Mayor Oh identified the Inner Ring Road and Bukbu Expressway as the main reasons for the development delays in the Gangbuk area. He stated, "Although the Inner Ring Road and Bukbu Expressway have been the only east-west transportation corridors in the Gangbuk region, the roads remain unchanged from 30 years ago, and their average speed is only 35 kilometers per hour, meaning they have lost their function as major arterial roads."
In addition, the aging elevated structures are increasing maintenance costs. The city expects maintenance costs for the Inner Ring Road and Bukbu Expressway to more than double, from 39.1 billion won in 2024 to 98.9 billion won in 2055. This situation is escalating both safety risks and fiscal burdens.
The Seoul Metropolitan Government anticipates that the underground city expressway will provide a smooth traffic flow with an average speed of 67 kilometers per hour. In particular, the surface roads will be improved to enhance connectivity and accessibility between regions. For example, the city plans to restore Hongjecheon and Mukdongcheon, which suffered environmental degradation due to the elevated roads, and create new riverside leisure spaces. The city expects that, once the project is completed, the urban environment for approximately 2.8 million residents in 134 neighborhoods across eight districts in Gangbuk will be greatly improved, and that the project will have a transformative effect on regional competitiveness and urban vitality.
Starting next year with the preparation of detailed implementation plans, the city aims to complete design and preliminary procedures between 2026 and 2029, begin construction in 2030, and finish the entire project by 2037. To minimize inconvenience for road users, construction of the underground expressway will begin first, and the surface-level demolition will take place after the new route opens.
To ensure smooth project implementation, the city will establish the "Gangbuk Renaissance Planning Group," a dedicated organization involving citizens, experts, and district offices. This organization will operate three divisions: housing and urban development, roads and transportation, and culture and welfare. Through this public-private-academic consultative body, the city will hold working-level meetings, public hearings, and various forums to gather diverse opinions.
Mayor Oh stated, "The large-scale remodeling of Gangbuk's road space is a massive project that will require a substantial budget and more than ten years to complete. It is not just a simple road improvement, but a catalyst to usher in a new era for Gangbuk. We will do our utmost to ensure the project's smooth progress, raising Gangbuk's competitiveness and quality of life to the next level."
The view of Jeongneung-ro (right) after the demolition of the elevated road following the "Gangbuk Transversal Underground City Expressway Construction Plan." Seoul City
The appearance of Mukdongcheon after the demolition of the elevated road following the "Gangbuk Transverse Underground City Expressway Construction Plan" (right). Seoul City
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