Take the two longest undersea tunnels in the world -- Japan's Seikan Tunnel at 23.3 kilometers and the English Channel Tunnel at 37.9 kilometers -- and combine them. The proposed Bohai Strait Tunnel would still be longer. At 123 kilometers total, with 90 kilometers underwater, this project would connect Dalian on the Liaodong Peninsula to Yantai on the Shandong Peninsula, replacing an eight-hour ferry crossing with a 40-minute train ride. It would also be one of the most expensive infrastructure projects ever attempted, with a budget that has risen to 300 billion yuan -- roughly 43 billion US dollars.
The Bohai Strait is the narrow bottleneck connecting the Bohai Sea to the Yellow Sea. It separates two of China's most economically important peninsulas: Liaodong in the northeast, anchored by the port city of Dalian, and Shandong to the southeast, home to Yantai and the broader manufacturing corridor. Today, the only direct connection between the two is the Bohai Train Ferry, inaugurated in 2007, which takes eight hours to cross. The alternative is a 1,400-kilometer drive around the entire Bohai Sea through Hebei Province. The strait is not wide -- about 100 kilometers -- but without a fixed crossing, the two peninsulas function as separate economic zones despite their proximity. The tunnel would change that overnight, linking them to China's high-speed rail network and allowing cars to be loaded onto railway carriages for the crossing.
The proposed route is not a simple line from point A to point B. Plans submitted to the National Development and Reform Commission in May 2019 envision a hybrid structure: bridges from Penglai linking the Changshan Islands, the archipelago that dots the southern strait, and then a tunnel beneath the deeper, open-water section of the Bohai Strait. The total length, including the bridge segments, would reach 125 kilometers. The Changshan Islands provide convenient intermediate points for the bridge portions, reducing the open-water spans and offering potential locations for ventilation and emergency access. China Railway Engineering Corporation would operate the tunnel, integrating it into the country's high-speed rail system. The engineering challenges are formidable: deep water, seismic activity, and the enormous pressures of a tunnel that would run tens of meters below the seafloor for 90 kilometers.
The tunnel concept has been discussed since at least 2013, when National People's Congress deputies formally proposed a cross-Bohai-Strait connection. In March 2018, the central government expressed interest in getting construction underway 'as soon as possible.' By 2019, when formal plans were submitted for approval, the estimated budget had risen to 300 billion yuan. If construction had started in 2020 as originally hoped, the opening date would have been in the early 2030s. The project belongs to a category of Chinese mega-infrastructure that includes the Hong Kong-Zhuhai-Macau Bridge, the proposed Taiwan Strait Tunnel, and the Qiongzhou Strait tunnel to Hainan Island. Whether the Bohai Strait Tunnel will move from proposal to construction depends on political will, economic calculations, and the technical confidence that 90 kilometers of undersea tunnel can be built safely. If it is ever completed, it will be the longest undersea tunnel in the world by a factor of nearly two.
The proposed tunnel route crosses the Bohai Strait at approximately 38.30N, 120.90E, connecting Dalian (ZYTL) to the north and Yantai (ZSYT) to the south. The Changshan Islands are visible in the strait as stepping stones for the bridge portions of the route. The strait itself is clearly visible from altitude as the narrow passage between the Bohai Sea and Yellow Sea. Best viewed at 10,000-20,000 ft for the full strait overview.