Switzerland's Gotthard Base Tunnel is world's longest and deepest tunnel
The Channel Tunnel, between the UK and France, has world's longest undersea section
This year marks the 20th anniversary of the opening of the Channel Tunnel linking France with the United Kingdom, and the 50th anniversary of the deal which led to its creation.
The Gotthard Base Tunnel, dubbed Switzerland’s “construction of the century,” was 17 years in the making and is reported to have cost around $12 billion.
To mark the occasion, we’re taking a look at some of the world’s greatest tunnels.
1. Gotthard Base Tunnel (Switzerland)
European leaders including German Chancellor Angela Merkel and French President Francois Hollande turned out for the Gotthard’s Base Tunnel’s grand opening in June, which featured colorful and often surreal scenes involving costumed dancers, fireworks and plenty of yodeling.
Reaching a depth of 2,300 meters (7,545 feet, almost 1.5 miles) the tunnel will slice an hour off travel time between Zurich, Switzerland, and Milan, Italy.
The 57-kilometer tunnel runs between the towns of Erstfeld in the north and Bodio in the south. Trains reaching speeds of up to 250 kilometers an hour (155 mph) can travel through in 20 minutes, according to the Swiss Travel System.
Normal commercial traffic began in earnest on December 11, when the first regular passenger train left Zurich at 6.09 a.m. local time and arrived in Lugano at 8.17 a.m.
Gotthard overtakes the 53.9-kilometer Seikan Tunnel in northern Japan as the longest rail tunnel in the world and relegates the 50.5-kilometer Channel Tunnel between Britain and France into third place.
Length: 57 kilometers (35 miles)
Fast fact: 3,200 kilometers of copper cable was used in the tunnel’s construction – enough to stretch from Madrid to Moscow.
More info: Gotthard Base Tunnel
2. Channel Tunnel (England and France)
Connecting the United Kingdom with continental Europe (it has entrances/exits in Folkestone, Kent, and Pas-de-Calais in northern France), the tunnel has the world’s longest undersea section – 37.9 kilometers (23.5 miles).
Though a marvel of the modern age, it wasn’t a new idea when it was built.
“This tunnel defined the term ‘mega project,’” says Matt Sykes, tunnel expert and director at engineering company Arup.
“It fundamentally changed the geography of Europe and helped to reinforce high speed rail as a viable alternative to short-haul flights.”
Length: 50 kilometers (31 miles)
Fast fact: Though both the English and French put in work to build the Channel Tunnel, the English side tunneled a greater distance.
More info: Euro Tunnel
3. Laerdal Tunnel (Aurland, Norway)
The Laerdal Tunnel in West Norway is the world’s longest road tunnel and cost $153 million to build, which works out at $6,250 per meter.
“The sheer length of tunnel – which takes 20 minutes to drive through – led to innovation in the use of behavioral science and driver psychology in the design to reduce driver fatigue and improve safety,” says Sykes.
“This resulted in large, colorfully lit caverns every six kilometers, providing points of interest and a unique driver experience.”
Length: 24.5 kilometers (15.2 miles)
Fast fact: Engineers separated the tunnel into different sections to give the illusion that drivers are traveling through a number of smaller tunnels.
More info: The Fjords
4. Tokyo Bay Aqua-Line (Tokyo)
It’s easy to mistake this tunnel for a bridge because part of the structure comprises a 4.4-kilometer span as well as a 9.6-kilometer subsea conduit.
The Aqua Line crosses Tokyo Bay and connects the cities of Kawasaki and Kisarazu.
“This project required the world’s largest undersea tunnel boring machines and set the precedent for constructing two-lane road tunnels,” points out Matt Sykes at Arup.
Length: 14 kilometers total (8.7 miles)
Fast fact: Constructed atop the Tokyo Bay Aqua Line is an island that functions as a rest area and mall.
The man-made island, called Umi-Hotaru, is a popular scenic point with an observation deck that gives a great view of Tokyo Bay.
More info: Nippon Civil Consulting Engineers
5. Eisenhower Tunnel (Colorado)
Colorado’s Eisenhower road tunnel is one of the world’s highest, located 3,401 meters (11,158 feet) above sea level, at the highest point on the U.S. interstate highway system.
It played a significant role in the women’s rights movement when Janet Bonnema was hired as a construction worker in 1972.
Bonnema sued and was allowed to return to the tunnel.
Length: 2.72 kilometers (1.7 miles)
Fast fact: Prior to the tunnel’s official opening in 1972, a drunk driver believed he should be the first person to take a vehicle through and was arrested for trespassing.
More info: Colorado Department of Transportation
6. Spiralen Tunnel (Drammen, Norway)
The dramatic Spiralen road tunnel, built in 1961 and comprising six spirals covering 1,649 meters (5,413 feet), leads to one of the most spectacular viewpoints in the industrial town of Drammen.
“Despite being an expensive country, Norway builds some of the cheapest tunnels,” says Alun Thomas, head of tunnels at engineering consultancy Ramboll.
Length: 1.65 kilometers (1.02 miles)
Fast fact: The tunnel opens out to a dramatic view of Drammen Valley and has a beer garden, restaurants and open-air museum.
More info: Spiralen in Drammen
7. Guoliang Tunnel (Henan Province, China)
Before the construction of this impressive tunnel, the only way to access the village of Guoliang was via a narrow path carved into the side of the Taihang Mountains.
Three died during the construction process but the tunnel transformed the village and became a tourist attraction in its own right.
“This tunnel is beautiful and a tribute the tenacity of the villagers who built it,” says Thomas at Ramboll.
Length: 1.2 kilometers (0.74 miles)
Fast fact: The tunnel was built jagged and steep due to the village’s primitive tools, earning it the nickname: “The road that does not tolerate any mistakes.”
8. SMART (Kuala Lumpur, Malaysia)
“SMART is a combined road and flood relief tunnel,” explains Thomas at Ramboll.
The tunnel, the longest in Malaysia, was built to solve the problem of flash flooding in Kuala Lumpur.
When there’s no flooding, it serves purely as a road tunnel.
When there are floods, rainwater can be diverted into a lower channel, and the upper level will remain open to traffic.
When exceptionally heavy floods occur, the tunnel closes to all traffic and watertight gates open to allow floodwater to flow through.
Length: 9.7 kilometers (6.02 miles)
Fast fact: The tunnel is expected to prevent billions of dollars of possible flood damage and costs from traffic congestion.
More info: SMART Motorway Tunnel
9. Bund Sightseeing Tunnel (Shanghai)
This underwater Chinese tunnel is short and sweet, but spectacular and slightly strange.
Length: 646.7 meters (2,122 feet)
Fast fact: A company that had worked with Disney was originally supposed to help design the tunnel, but was deemed too expensive.
10 Seikan Tunnel (Japan)
The Seikan is a railway tunnel in Japan, but what makes it unique is the fact that a 23-kilometer (14.2 miles) stretch of the tunnel is 140 meters (460 feet) below sea level.
It spans the Tsugaru Strait, connecting Aomori Prefecture on the island of Honshu to the island of Hokkaido. Work on the tunnel started in 1964 and was completed in 1988.
Length: 53 kilometers (32.9 miles)
Fast fact: In 1976, construction workers hit a patch of soft rock and water gushed into the tunnel at a rate of 80 tons per minute. The leak took two months to fix.
More info: JR-Hokkaido Hakadote Branch
CNN’s Tim Hume, Hilary Whiteman, George Webster, Tamara Hinson, Sofia Couceiro and Maureen O’Hare contributed to this report.