The Inner Ring Road and the Bukbu Arterial Road in northern Seoul will be put underground, and the existing overpasses will be demolished.
Oh Se-hoon, the Seoul mayor, on the 18th announced a plan for "construction of an underground urban expressway crossing northern Seoul" at the main conference room of Seoul City Hall. Oh said, "The Inner Ring Road, which opened in 1995, carries an average of 130,000 vehicles a day, and the Bukbu Arterial Road, which opened in 1997, carries 90,000," adding, "The problem is that while the surrounding areas have been developed and traffic volumes have surged, the roads have remained the same, resulting in chronic congestion. The average commute speed is only about 35 kph."
Oh said, "There are currently 139 zones undergoing redevelopment around the arterial roads, and when the projects are completed, the number of households will increase by about 40,000, so we expect congestion to worsen." Oh also said, "Maintenance costs for overpasses rise sharply after about 40 years," adding, "Usage restrictions on overpasses due to safety issues could arise soon."
The city will build an underground road along about 20.5 kilometers beneath the Inner Ring Road and the Bukbu Arterial Road. In phase one, it will first push the Seongsan–Hawolgok–Sinnae section, and the remaining Inner Ring section, Hawolgok–Seongdong, will be pursued in phase two. Oh said, "We will prepare detailed execution plans next year, with a goal of completion in 2037, 12 years from now."
The existing overpasses will be demolished after opening. Beneath the Inner Ring and the Bukbu Arterial Road, a six-lane, bidirectional underground urban expressway will open. At ground level, a two-lane road will be added. The city will also restore Hongje Stream and Mukdong Stream, where the environment was degraded by the overpasses, to create waterfront leisure spaces.
The city estimates the project cost at 3.4 trillion won. Oh said, "Seoul's annual budget is a little over 51 trillion won. Assuming we invest about 300 billion won a year over 12 years, the share of the total budget would be just under 0.6%." Oh added, "We considered a private investment model, but we are leaning heavily toward funding it entirely with public finances."
To ensure steady progress, the city plans to establish and operate the Gangbuk Renaissance Planning Group, a joint task force of relevant bureaus. It also plans to form a public–private–academic council with the city, district offices, local residents, and experts. Oh said, "The project to build the east–west underground urban expressway in northern Seoul will be a key strategy of 'Again, the heyday of Gangbuk,' dramatically improving the region's competitiveness."