From Tokyo to Ulaanbaatar: 10 Infrastructure Projects to Watch Across East Asia

From Tokyo to Ulaanbaatar: 10 Infrastructure Projects to Watch Across East Asia

Beneath central Tokyo, a heavily used section of urban expressway is being rebuilt while the transport system around it continues operating.

The 1.8 km Nihonbashi section of the Metropolitan Expressway carries around 100,000 vehicles a day. Its ageing elevated structures are being replaced by a new underground route, with construction proceeding alongside redevelopment around the Nihonbashi River. The underground road is scheduled to open in fiscal 2035, followed by removal of the existing elevated expressway by fiscal 2040.

Japan, South Korea and Taiwan already possess extensive transport, power and urban networks. Their largest current projects frequently have to pass beneath cities, connect into operating railways or replace infrastructure without stopping the systems around them.

The conditions change sharply in Mongolia. There, new railways and power projects are still filling fundamental gaps across enormous distances, including only the second direct cross-border railway connection with China in more than 70 years.

Briefing

• Japan’s Chuo Shinkansen combines superconducting maglev technology with extensive deep underground and mountain tunnelling, with full-scale shield excavation continuing during 2026.
• Around 80% of the 212 km Hokkaido Shinkansen extension to Sapporo is in tunnel, with major breakthroughs achieved during 2026.
• South Korea’s GTX-B and GTX-C projects are extending high-speed metropolitan rail across the Seoul Capital Area, with GTX-C formally entering construction in September 2026.
• Taiwan has major metro and railway reconstruction programmes under way in Taoyuan and Kaohsiung, including extensive underground works through established urban areas.
• Mongolia is constructing a new railway connection with China while the 90 MW Erdeneburen Hydropower Project has reached a reported 40% construction progress.

1. Chuo Shinkansen, Japan

The Chuo Shinkansen is attempting something that Japan’s existing high-speed railway network does not: commercial intercity operation using superconducting magnetic levitation.

JR Central’s line is being developed between Tokyo and Osaka via Nagoya, with the first stage linking Shinagawa and Nagoya. Much of the alignment will be underground or in mountain tunnels, including deep sections beneath the Tokyo metropolitan area.

Construction continued across multiple locations during 2026. JR Central’s September updates show full-scale shield excavation under way on sections of the First Metropolitan Area Tunnel in Tokyo and Kanagawa, accompanied by monitoring of ground movement, vibration, noise and groundwater.

Stations, shafts, viaducts, mountain tunnels and the existing Yamanashi Maglev Line all have to become parts of a railway designed around a technology fundamentally different from the steel wheel and rail used by the Shinkansen since 1964.

The project has also had to negotiate environmental concerns in Shizuoka Prefecture, where the proposed alignment passes beneath the Southern Alps. In July 2026, Shizuoka gave the project an important approval following years of disagreement over environmental issues, allowing preparations for construction in the prefecture to move forward.

2. Hokkaido Shinkansen Extension, Japan

Farther north, the extension of the Hokkaido Shinkansen from Shin-Hakodate-Hokuto to Sapporo is being shaped by geology.

The new section extends for approximately 212 km, with roughly 169 km, or about 80%, running through tunnels. The proportion leaves relatively little conventional open railway construction along the route.

Several substantial tunnelling milestones were reached during 2026. The 17.975 km Shiribeshi Tunnel achieved breakthrough in June, while excavation of the 5.569 km Hirafu section of the Yotei Tunnel was completed in August. Work was continuing on other sections in September.

Progress has not been straightforward. Difficult geological conditions have affected construction schedules and contributed to substantial delay in the expected opening of the extension. The project is now associated with a much later opening than originally planned, with the construction authority continuing to assess the programme as work advances through the remaining tunnels.

Long tunnels, difficult geology and construction logistics in Hokkaido remain dominant features of the programme despite decades of Japanese experience building high-speed rail.

3. Nihonbashi Expressway Undergrounding, Japan

The Metropolitan Expressway between Kandabashi Junction and Edobashi Junction extends for around 1.8 km and carries approximately 100,000 vehicles each day. Its elevated structures require renewal after decades of intensive use.

Rather than reconstructing the expressway in essentially the same form, the route is being taken underground. Construction has been progressing since 2020, while a long-term closure of the Yaesu Route began in April 2025 as the programme moved into its main underground phase. The underground route is scheduled for completion in fiscal 2035, with removal of the old elevated structures planned to finish in fiscal 2040.

The construction takes place in one of Tokyo’s most intensely developed districts, alongside the Nihonbashi River and major redevelopment projects. During 2026, underground works were sufficiently advanced for Tokyo’s governor and Japan’s transport minister to inspect the works from the river.

The project combines structural renewal with a fundamental rearrangement of the space occupied by the expressway. When the elevated structure is eventually removed, a road that has dominated the river corridor for generations will have been transferred beneath it.

4. GTX-B, South Korea

The Seoul Capital Area is building a new layer of railway beneath and through one of the world’s largest metropolitan regions.

GTX-B is an approximately 82.8 km high-speed metropolitan railway connecting the Incheon area in the west with Maseok in Namyangju to the east. It is planned with 14 stations and combines publicly funded and privately financed sections.

Construction began in 2025 and continued through 2026, with the South Korean Ministry of Land, Infrastructure and Transport listing the line among the GTX projects under active construction management.

The publicly funded Yongsan-Sangbong section includes substantial underground civil engineering and interchange construction. Individual packages include tunnelling and work around existing stations, where the new railway has to connect with Seoul’s dense metro and conventional rail network.

GTX is designed around longer metropolitan journeys than conventional urban metro lines, linking outer parts of the capital region with major employment and transport centres through higher-speed services. GTX-B therefore occupies the space between an urban metro and an intercity railway across a metropolitan region that has expanded far beyond central Seoul.

5. GTX-C, South Korea

GTX-C moved from planning into physical construction on 15 September 2026.

The approximately 86.5 km route will run between Deokjeong in the north and Suwon in the south, crossing the Seoul Capital Area and connecting with established rail and metro infrastructure along the way.

Its construction start followed a prolonged period of commercial and administrative adjustment. A revised implementation agreement cleared South Korea’s Private Investment Project Deliberation Committee in August, allowing construction contracts, financing arrangements and the formal commencement process to proceed.

The line will use a combination of new infrastructure and established transport corridors through a densely developed region. Much of the difficult work will be underground or around existing railway infrastructure, where new high-speed metropolitan services have to be inserted without treating the capital region as an empty construction site.

6. Taoyuan Metro Green Line, Taiwan

In Taoyuan, construction of a 27.8 km metro is approaching its later stages.

The Green Line will contain 21 stations, with approximately 12.5 km underground and 15.3 km elevated. Ten stations are underground and 11 elevated, giving the project a mixture of tunnelling, viaduct, station and systems construction.

By October 2026, overall construction progress had reached 72.67%.

The GC02 package includes approximately 10.52 km of tunnel, with 6.24 metre diameter shield machines being used to construct ten running tunnels. Some drives operate at depths of around 25 to 37 metres, including stacked tunnel arrangements approaching Taoyuan railway station.

The completed Green Line will connect parts of Taoyuan with the city’s developing rail network and the airport corridor. It is being constructed as part of a wider programme, with an extension towards Zhongli also moving through construction and procurement during 2026.

7. Taoyuan Railway Undergrounding, Taiwan

A second Taoyuan project deals with an older railway rather than a new metro.

The Taoyuan railway undergrounding programme is rebuilding sections of the existing Taiwan Railway corridor below ground while maintaining railway operations through temporary tracks and staged construction.

By October 2026, the overall programme was reported at 37.22% complete. Multiple civil packages were already under construction, including underground works around Taoyuan, Zhongli, Zhongyuan and Pingzhen, while other permanent track, signalling, ventilation and systems packages remained to be procured.

The staging is as important as the permanent works. Temporary tracks, temporary station facilities, signalling and control systems have to maintain railway services while the permanent alignment is reconstructed beneath the city.

The existing railway has shaped Taoyuan’s urban development for decades, leaving the project to work around roads, utilities, buildings, stations and continuing train movements before the surface occupied by the old alignment can eventually be reorganised.

8. Kaohsiung MRT Yellow Line, Taiwan

Kaohsiung is constructing another major underground rail corridor across the southern Taiwanese city.

The Yellow Line extends for 22.91 km and will have 23 stations, of which 22 are underground and one elevated. The route crosses established districts including Niaosong, Sanmin, Fengshan, Lingya and Qianzhen.

By October 2026, overall progress stood at approximately 13.35%, with work under way on the depot, retaining structures, drainage and station infrastructure. With 22 of its 23 stations underground, most of the new railway has to be inserted beneath established roads and neighbourhoods rather than developed along a new surface corridor.

The project also includes three energy dispatch centres and the mechanical and electrical systems for all 23 stations. It will add another axis to a Kaohsiung network that already includes the Red and Orange metro lines and the completed circular light rail.

9. Gashuunsukhait-Gantsmod Cross-Border Railway, Mongolia

At Mongolia’s southern border, railway construction is solving a problem measured in only a few dozen kilometres but with consequences for a much larger freight system.

On-site construction of the Gashuunsukhait-Gantsmod cross-border railway officially began on 15 June 2025, when drilling started for the first bridge foundation pile at the Mongolia-China border. The project creates a new rail connection at one of the principal gateways for Mongolian mineral exports.

The complete project is approximately 32.6 km long and incorporates both Mongolia’s 1,520 mm broad gauge and China’s 1,435 mm standard gauge. It is designed for an annual freight capacity of around 40 million tonnes. The works include approximately 19.5 km of main railway together with bridge structures, stations, border-control facilities and associated infrastructure.

By January 2026, the overall programme was reported at 9.75% complete, with piling, bridge foundations, culverts and temporary access works under way. A March inspection again confirmed active construction.

Mongolia’s Railway Authority describes it as the country’s second cross-border railway with China since the Zamyn-Uud-Erlian connection established under the 1955 agreement.

For a landlocked country whose mineral exports depend heavily on access to Chinese markets, completing the missing railway across the border removes a physical break in a freight corridor that already handles enormous volumes by road.

10. Erdeneburen Hydropower Project, Mongolia

On the Khovd River in western Mongolia, construction is under way on a 90 MW hydropower station.

Construction of the Erdeneburen Hydropower Project began in July 2025 under a turnkey contract with PowerChina. By September 2026, Mongolia’s Ministry of Energy reported that construction had reached approximately 40%.

The remaining works include closure of the diversion structure, excavation of the main water-intake tunnel and concrete lining. More than 580 workers from Mongolia, China and Bangladesh were reported to be working at the site in September.

The plant is designed to generate approximately 360 million kWh annually and is scheduled for completion in May 2030. The contract is valued at around US$266.45 million and is being supported by Chinese concessional financing.

Western Mongolia is geographically remote from the country’s principal generating capacity and has historically relied partly on imported electricity. Erdeneburen will add substantial domestic generation closer to western demand, while requiring the dam, waterways, generating equipment and transmission infrastructure to be assembled in a region where distance itself shapes construction logistics.

Building Without an Empty Map

Japan, South Korea and Taiwan are increasingly building infrastructure within the physical limits created by earlier generations of development. Tunnels pass beneath cities and mountains, temporary railways keep passengers moving while permanent tracks are rebuilt, and new metropolitan lines have to connect with networks already carrying millions of journeys.

Japan’s two Shinkansen projects add geology to those constraints. The Chuo Shinkansen combines a new propulsion system with deep urban and mountain tunnelling, while the Hokkaido extension is advancing through ground that has already pushed its construction programme far beyond the original timetable.

Mongolia faces a different map. The Gashuunsukhait-Gantsmod railway is creating only the country’s second rail connection with China, while Erdeneburen is adding domestic generation in a western region separated by enormous distances from Mongolia’s principal power system.

From Tokyo’s underground expressways to a new railway across the Mongolian border, East Asia’s construction programme is being shaped by what surrounds the project before work begins: cities, mountains, operating infrastructure, borders and distance.

Key Industry Questions

1. What is the Chuo Shinkansen? It is a new Japanese intercity railway being developed by JR Central using superconducting magnetic-levitation technology. The route will ultimately connect Tokyo and Osaka via Nagoya, with extensive tunnel construction.
2. How much of the Hokkaido Shinkansen extension is underground? Approximately 169 km of the 212 km Shin-Hakodate-Hokuto to Sapporo extension is in tunnel, equivalent to roughly 80% of the route.
3. Why is Tokyo putting the Nihonbashi Expressway underground? The existing elevated expressway requires major renewal. Reconstructing it underground also allows the elevated structures above the Nihonbashi River to be removed as part of wider urban redevelopment.
4. What are South Korea’s GTX railways? The Great Train eXpress network is a series of high-speed metropolitan rail corridors intended to reduce longer-distance journey times across Seoul, Incheon and Gyeonggi Province.
5. How long is GTX-B? GTX-B is approximately 82.8 km long and will connect the Incheon area with Maseok through central Seoul, with 14 stations planned.
6. How advanced is the Taoyuan Metro Green Line? Taoyuan City reported overall progress of 72.67% by October 2026. The 27.8 km line includes 21 stations and both underground and elevated sections.
7. How much of Kaohsiung’s Yellow Line will be underground? The 22.91 km line will have 23 stations. Twenty-two will be underground and one elevated.
8. What is unusual about the Gashuunsukhait-Gantsmod railway? It incorporates both Mongolia’s 1,520 mm broad gauge and China’s 1,435 mm standard gauge and will create only the second railway border connection between the two countries.
9. How large is the Erdeneburen Hydropower Project? The plant will have 90 MW of installed capacity and is designed to produce approximately 360 million kWh of electricity annually.
10. Why are so many major infrastructure projects in Japan, South Korea and Taiwan being built underground? Dense urban development and mountainous terrain leave limited space for new surface corridors. Tunnelling allows additional transport capacity to be inserted beneath existing development and operating infrastructure.

Strategic Takeaways

1. Dense existing development is pushing a substantial share of Japanese, Korean and Taiwanese transport investment underground, increasing the importance of tunnelling, monitoring and staged construction.
2. Existing infrastructure increasingly determines how new infrastructure must be built, particularly where construction has to proceed around operating railways, roads and utilities.
3. The Chuo and Hokkaido Shinkansen projects show that geology and construction access can dominate railway programmes even where the underlying transport technology is well established.
4. South Korea’s GTX programme is treating metropolitan rail increasingly as a regional network, connecting employment and residential centres far beyond central Seoul.
5. Mongolia’s infrastructure priorities remain fundamentally different, with cross-border connectivity and domestic energy supply still capable of changing the basic geography of national networks.

Explore the Global Infrastructure Series

This article is part of Highways.Today’s global review of 110 infrastructure projects across 11 regions, examining the major transport, energy and civil engineering projects shaping investment and construction around the world.

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