Top 10 Longest Tunnels in the World

The Gotthard Base Tunnel in Switzerland is the longest and deepest traffic tunnel in the world, stretching 57.09 kilometers through the Swiss Alps. Completed in 2016 after 17 years of construction, it carries high-speed rail traffic between Zurich and Milan, reducing travel time by over an hour and shifting freight transport from road to rail.

Introduction

Tunnel engineering has advanced dramatically in recent decades, driven by tunnel boring machines (TBMs) that can cut through rock at speeds of up to 30 meters per day. The longest tunnels now span entire mountain ranges and seabeds, connecting countries and transforming transportation networks. These subterranean highways represent some of the most ambitious infrastructure projects in human history.

1. Gotthard Base Tunnel, Switzerland — 57.09 km

• Length: 57.09 km
• Type: Rail tunnel
• Maximum Depth: 2,300 m below surface
• Completed: 2016
• Cost: ~$12 billion

The Gotthard Base Tunnel consists of two single-track tubes connected by cross-passages every 325 meters. At its deepest point, the tunnel lies 2,300 meters below the peaks above, making it not only the longest but also the deepest traffic tunnel ever built. Up to 260 freight trains and 65 passenger trains pass through it daily.

Construction required excavating 28.2 million tonnes of rock, primarily gneiss and granite. Workers encountered geological challenges including zones of soft rock, high-pressure groundwater, and temperatures reaching 46 degrees Celsius at the deepest points. Nine workers died during the 17-year construction period.

2. Seikan Tunnel, Japan — 53.85 km

• Length: 53.85 km (23.3 km undersea)
• Type: Rail tunnel
• Location: Tsugaru Strait, Hokkaido–Honshu
• Completed: 1988
• Cost: ~$7 billion

The Seikan Tunnel connects the Japanese islands of Honshu and Hokkaido beneath the Tsugaru Strait. Its 23.3-kilometer undersea portion was the longest of any tunnel in the world until the Channel Tunnel opened in 1994. The tunnel took 24 years to build, beginning in 1964 after a devastating typhoon sank five ferries in the strait in 1954.

The tunnel descends to 240 meters below sea level and 100 meters below the seabed. It was originally built for Shinkansen high-speed trains, though conventional trains used it for decades. The Hokkaido Shinkansen began operating through the tunnel in 2016, cutting Hokkaido-Tokyo travel time dramatically.

3. Channel Tunnel, UK–France — 50.45 km

• Length: 50.45 km (37.9 km undersea)
• Type: Rail tunnel
• Location: Strait of Dover, English Channel
• Completed: 1994
• Cost: ~$21 billion (adjusted)

The Channel Tunnel, known as the Chunnel, connects Folkestone in England with Coquelles in France beneath the English Channel. Its 37.9-kilometer undersea section remains the longest of any tunnel in the world. The tunnel consists of two rail tunnels plus a central service tunnel, all bored through a consistent chalk marl layer beneath the seabed.

Over 13,000 workers constructed the tunnel from both ends simultaneously, meeting in the middle on December 1, 1990. Eurostar passenger trains reach speeds of 160 km/h through the tunnel, completing the undersea crossing in about 20 minutes. Vehicle shuttle trains carry cars and trucks between the two terminals.

4. Lötschberg Base Tunnel, Switzerland — 34.57 km

• Length: 34.57 km
• Type: Rail tunnel
• Location: Bernese Alps, Switzerland
• Completed: 2007

The Lötschberg Base Tunnel runs through the Bernese Alps in Switzerland, serving as a key link in the north-south European rail corridor. It was the longest land tunnel in the world when it opened in 2007, before being surpassed by the Gotthard Base Tunnel in 2016. The tunnel carries both passenger and freight trains at speeds up to 250 km/h.

Only one of the two planned tubes was fully completed; the second tube was partially excavated but left unfinished due to budget constraints. Plans to complete the second tube have been approved and construction is expected to begin in the coming years, which will double the tunnel's capacity.

5. New Guanjiao Tunnel, China — 32.65 km

• Length: 32.65 km
• Type: Rail tunnel
• Location: Qinghai Province, China
• Completed: 2014

The New Guanjiao Tunnel is located on the Qinghai-Tibet railway in western China, at an average elevation of approximately 3,300 meters above sea level. It is the longest high-altitude railway tunnel in the world, replacing an older, shorter tunnel and a winding mountain route that was prone to landslides and severe weather.

Construction at such extreme altitude presented unique challenges, including low oxygen levels for workers, permafrost zones, and temperatures dropping below -30 degrees Celsius in winter. The tunnel reduced the railway distance through the Guanjiao Mountain section by 20 kilometers and eliminated altitude variations that slowed trains.

Key Facts

• The Gotthard Base Tunnel at 57.09 km is the longest traffic tunnel in the world.
• The Channel Tunnel has the longest undersea section at 37.9 km.
• The Seikan Tunnel took 24 years to complete.
• Switzerland alone contains two of the five longest tunnels on Earth.
• Modern tunnel boring machines can excavate up to 30 meters per day.

Fun Facts

• The rock temperature at the deepest point of the Gotthard Base Tunnel reaches 46 degrees Celsius — requiring massive cooling systems.
• The Channel Tunnel was first proposed by Napoleon in 1802.
• The Seikan Tunnel was built after a typhoon sank five ferries and killed over 1,400 people in 1954, motivating a fixed link.
• Workers boring the Channel Tunnel from opposite sides met with a misalignment of only 36 centimeters.

Final Thoughts

The world's longest tunnels are testaments to human ingenuity, connecting islands, spanning mountain ranges, and linking nations beneath the sea. As tunnel boring technology continues to advance, even longer tunnels are being planned, including proposals for fixed links across the Strait of Gibraltar and the Bering Strait.