Seoul's light rail construction projects have been adrift for a long time. Of the seven new lines included in the Second Seoul urban rail network construction plan that the city released in 2019, five have not even broken ground. The Gangbuk transverse line, Mokdong line, and Nangok line failed to pass the preliminary feasibility study, while the Seobu line, being pursued as a private investment project, has stalled as its business case worsened. The Wirye–Sinsa line, which had been pushed as a private project, ultimately foundered and was converted to a fiscal project. The city set out plans to seek improvements to the preliminary feasibility study system and to diversify project methods.
According to Seoul City on the 9th, the city plans to include the new Gangbuk transverse line and Mokdong line in the Third urban rail network construction plan and push them again. The city is drawing up the Third urban rail network construction plan and will readjust routes and stations and then reapply for preliminary feasibility studies for the relevant lines.
The Gangbuk transverse line is a 25.73-kilometer light rail line consolidating Mokdong Station in Yangcheon District and Cheongnyangni Station in Dongdaemun District. In the 2024 preliminary feasibility study, its benefit-cost ratio (B/C, the ratio of the present value of total benefits to the present value of total expense) was 0.57, below 1, failing to secure economic feasibility and being dropped. The Mokdong line, consolidating Sinwol-dong in Yangcheon District with Dangsan Station in Yeongdeungpo District, also posted a low B/C in the same year and failed to clear the preliminary feasibility threshold. The Nangok line is undergoing a preliminary feasibility study.
A preliminary feasibility study is a system, overseen by the Ministry of Planning and Budget, that verifies in advance the validity of road or rail construction projects that require fiscal spending; without passing it, a project cannot proceed at all. The city has been calling for improvements to the system. Currently, in the Seoul metropolitan area, the weighting is 60% to 70% for economic feasibility and 30% to 40% for policy relevance. The city says the policy share should be raised with more focus on citizen benefits and economic ripple effects. Lee Jingu, Seoul's transportation planning director, said, "We plan to propose to the government improvements to the preliminary feasibility system, such as readjusting the weighting between economic feasibility and policy relevance."
While the prevailing view is that expanding light rail lines is necessary to improve residents' quality of life and transportation convenience, there is no shortage of skepticism. An official at a construction company said, "Even if lines with lower demand than those in the city center are forced to fit the criteria to pass the preliminary feasibility study, operating losses later will hold them back," adding, "With local elections approaching, many local government heads are tossing out empty checks to win votes without concern for tax revenue, and there needs to be vigilance about this."
Private investment projects are even more blocked. The Seobu line is emblematic, with negotiations stalled over increased project costs. In the meantime, major builders such as Hyundai Engineering and GS Engineering & Construction have left the Seobu line consortium led by Doosan Engineering & Construction Co., worsening the situation. The city aims to diversify project methods and break ground in 2029, but both inside and outside the industry, calls are mounting to convert it to a fiscal project. Facing similar issues, the Wirye–Sinsa line, which had drifted for 17 years, was converted to a fiscal project last month and is undergoing the preliminary feasibility process.
In political circles, there are calls to legislate the reflection of inflation rates in project costs to expedite large-scale social overhead capital (SOC) private investment projects. Lawmaker Jeon Hyun-hee of the Democratic Party of Korea last month proposed a partial amendment to the Act on Private Participation in Infrastructure to adjust the total project cost in the implementation agreement upon completion by reflecting inflation. Yoo Jeong-hoon, president of the Korean Society of Transportation, said, "Major private transportation projects in the Seoul metropolitan area, including the Seobu line and GTX-C (Metropolitan Express Railway Line C), are at a standstill. Negotiations over project costs are not going well, and with no clear legal basis, responsible officials are taking a passive approach to problem-solving. It is necessary to legislate so that private projects also reflect inflation, just like fiscal projects."
Meanwhile, two of the seven lines that passed preliminary feasibility and are moving forward with construction are the Ui–Sinsa extension and the Myeonmok line. The Ui–Sinsa extension broke ground in November last year and aims to be completed in 2032. The Myeonmok line is slated to break ground in 2028.