Linking Japan’s Honshu and Hokkaido islands, the Seikan Tunnel is the world’s longest undersea rail tunnel (by overall length). Its origin traces back to 1954, when ferries were the main form of transport between Honshu and Hokkaido.
However, when a devastating typhoon claimed 1,430 lives in the Tsugaru Strait in 1954, engineers sought a safer path and, considering unpredictable weather, built a tunnel instead of a bridge to link the islands.
This extensive tunnel was completed in 1988, stretching an impressive 33.46 miles (53.85 kilometers) and about 790 feet (240 meters) below sea level. The tunnel includes two stations: Tappi Kaitei on Honshu Island and Yoshioka Kaitei on Hokkaido Island. These stations are the first railway stations constructed under the sea and serve as emergency escape points in case of a disaster.
Today, the Seikan Tunnel mainly handles freight trains, making the tunnel a crucial hub for transporting agricultural goods via freight trains.
The Channel Tunnel, nicknamed the Chunnel, spans 31.35 miles (50.49 kilometers) and links Folkestone, England, with Coquelles, France, underneath the English Channel at the Straits of Dover.
The UK and France agreed to create the Channel Tunnel in 1986, opting for a rail tunnel instead of a long bridge or a combination of road and rail to connect the two countries.
British Prime Minister Margaret Thatcher originally wanted a road tunnel rather than a railway service, possibly because cars “represented freedom and individualism.” However, a road tunnel was deemed too dangerous — it would have been extremely difficult to rescue people trapped in a pileup 15 miles (24 kilometers) out at sea.
Construction began on both sides of the Straits of Dover in 1987–88, concluding in 1991, with the tunnel officially opening on May 6, 1994. Today, it carries more than 10 million passengers annually and more than 1.6 million trucks on its rail-based shuttle service.
The design of the Channel Tunnel incorporates two single-track rail tunnels and one service tunnel, facilitating bi-directional traffic.
The Tokyo Bay Aqua-Line integrates road and rail through a 5.9-mile (9.6-kilometer) tunnel (with a total length of 14.7 miles, or 23.7 km) connecting Kawasaki and Kisarazu across Tokyo Bay in Japan. Opened on December 18, 1997, its route includes artificial island sections for a unique travel experience.
Comprising two 10-kilometer (2.6 miles)-long tunnels (Aqua Tunnel) beneath Kawasaki waters and a 5-kilometer (3.1 miles)-long bridge (Aqua Bridge) over Chiba waters, the expressway features two artificial islands, including “Umihotaru,” which stands out as Japan’s first marine rest area, strategically placed to transition the expressway from tunnels to bridges.
In addition, a tunnel ventilation tower named “Kazenotou” (Tower of Wind) is located on the artificial island in the mid-section of the undersea tunnel. The pyramid-shaped Ukishima Ventilation Station near the tunnel entrance on the Kawasaki side complements the overall design.
Located in Rogaland County, Norway, the Ryfast Tunnel System consists of two tunnels with a combined length of 8.9 miles (14.3 kilometers) beneath the sea.
The system includes two dual-lane tunnels: the Solbakk or Ryfylke tunnel, running from Solbakk to the island of Hundvag in Stavanger, and the Hundvag tunnel, connecting Hundvag to an underground tunneled highway interchange with the E39 Eiganes tunnel. As a part of the European Route E39 highway, the Ryfast Tunnel connects the towns of Strand and Hjelmeland.
The construction of the tunnel system spanned a decade and involved excavating more than 88 million cubic feet (2.5 million cubic meters) of rock. Ryfast Tunnel holds the record as the world’s deepest subsea road tunnel, reaching a maximum depth of 958 feet (292 meters) below sea level. Opened in 2020, the tunnel system serves as a replacement for the Høgsfjorden ferry crossing.
Opened in 2020, the Eysturoyartunnilin, known as the Eysturoy tunnel, spans an impressive 6.9 miles (11.2 kilometers) beneath the North Atlantic Ocean. It connects the two largest of the Faroe Islands, Streymoy and Eysturoy.
At its deepest point, this sub-sea passageway is 613.5 feet (189 meters) beneath the seabed. It features a unique network of three tubes; however, the most interesting part is the colorful intersection at its center—the world’s first and only sub-sea roundabout, famously named the “jellyfish roundabout.”
This underwater roundabout is a remarkable engineering feat and a feast for the senses, lit with captivating multicolored lights and featuring a sculpture and accompanying music.
6. Great Belt Bridge tunnel
Panoramic photo of the Great Belt Fixed Link (the East Bridge) taken from the Zealand side at sunset.
The Great Belt Bridge, also known as the Great Belt Fixed Link, is a marvel of engineering that consists of two bridges and a tunnel connecting the Danish islands of Zealand and Funen.
The tunnel, formally called the East Tunnel, is a railway tunnel that stretches an impressive 4.98 miles (8.02 kilometers), making it the second longest bored tunnel in Europe, after the Channel Tunnel. The tunnel features 31 connecting tunnels utilized for installations and emergency escapes.
The Great Belt Tunnel has significantly improved transportation between Zealand and Funen. It has cut travel time by approximately an hour, boosting regional trade and tourism. The tunnel also plays a crucial role in connecting Denmark to mainland Europe.
Situated in Møre og Romsdal county, Norway, the Eiksund Tunnel stretches more than 4.78 miles (7.68 kilometers) between the Norwegian mainland and Hareidlandet Island, off the Møre og Romsdal coast. The tunnel is part of a project that includes three tunnels and a bridge connecting several islands to the mainland. Operational since 2008, the tunnel serves as a replacement for the ferry route that connected the islands of Hareidlandet and Ulstein.
The construction of the Eiksund Tunnel was no small feat. Carved through the challenging geological formation of greenstone, which is prone to landslides, engineers employed rock bolting (a technique involving the insertion of steel bolts into drilled holes) to fortify the tunnel walls and prevent potential hazards.
The Eiksund Tunnel is a crucial transportation enhancement for the region. Slashing travel time between the two islands from around 45 minutes to just about 10, it not only facilitates efficient commuting but bolsters tourism and economic development in the surrounding area.
8. Qingdao Jiaozhou Bay Tunnel
The Qingdao Jiaozhou Bay Tunnel is an under-sea road tunnel located in eastern China’s Shandong Province. This tunnel runs beneath Jiaozhou Bay, linking Huangdao District to the south with Shinan District to the north.
Construction began on December 27, 2006, and concluded five years later, with the tunnel opening in 2011. The 4.8-mile (7.8-kilometer) tunnel includes underground and undersea sections, with a sub-sea portion covering 2.45 miles (~3.93 kilometers). The tunnel reaches a maximum depth of 242.7 feet (73.96 meters), with a maximum water depth of 137.7 feet (~41.94 meters).
A second Qingdao Jiaozhou Bay Tunnel is currently under construction to enhance connectivity across Qingdao’s coastal urban areas. The new 9.87-mile (~15.87-kilometer) tunnel will be longer than the Ryfast tunnel and have six lanes in both directions.
Named after the iconic North Cape on Magerøya island, the North Cape Tunnel is one of Norway’s longest and northernmost subsea road tunnels. King Harald V of Norway inaugurated the North Cape Tunnel on June 15, 1999.
Located in Nordkapp Municipality in Troms og Finnmark county in the far north of the country, it spans the Magerøysundet strait, connecting the mainland of Norway with the town of Honningsvåg and the tourist attractions at the North Cape.
Stretching about 4.3 miles (6.9 kilometers) and 696 feet (212 meters) below sea level at its deepest point, the tunnel replaced the previous ferry route between Kåfjord village and Honningsvåg.
RECOMMENDED ARTICLES
To combat the cold winters, the tunnel boasts automatic anti-freezing doors, locally known as “kuldeport.” These doors automatically seal the tunnel mouths in winter, preventing any leaked water from freezing and creating a hazard. When traffic is heavier in the summer, the gates remain open.
And that’s a wrap on today’s engineering extravaganza!
0COMMENT
NEWSLETTER
The Blueprint Daily
Stay up-to-date on engineering, tech, space, and science news with The Blueprint.
Sanjana Gajbhiye Sanjana, a passionate science writer, excels in simplifying complex ideas. With a belief that research is key, she's gained extensive knowledge through diverse roles as a writer and researcher. Beyond work, she finds solace in meditation and deeply appreciates art and culture.
0