Top 10 Longest Tunnels in the World

Channel Tunnel is a 50.45km rail tunnel that runs beneath the English Channel, connecting Folkestone, Kent in the UK with Coquelles near Calais in northern France. Known as a monumental project with its fair share of challenges, it was ultimately completed in 1994. Operated by Eurotunnel, it accommodates high-speed passenger trains, vehicle transport, and international freight services. In 1996, the American Society of Civil Engineers recognized it as one of the seven modern wonders of the world.

Though the idea of a tunnel connecting the two shores dates back to 1802, political pressure and concerns over national security delayed the project. However, the Channel Tunnel project finally began construction in 1988 and opened in 1994, surpassing its budget by 80%. Since its completion, the tunnel has faced several significant issues, including fires that delayed operations and illegal immigrants using it to enter the UK, leading to diplomatic tensions over the Sangatte refugee camp, which was closed in 2002. After repairs, the tunnel resumed full operation toward the end of 2008.

Lötschberg Base Tunnel runs approximately 400 meters beneath the Lötschberg mountain range through the Swiss Alps, opening in June 2007. The tunnel was constructed to reduce truck traffic on Switzerland's roads, making travel quicker for German tourists heading to Swiss resorts and cutting travel time between Valais and Bern by 50%. The total cost of the project was estimated at 4.3 billion Euros (as of 2007, with price adjustments made in 1998).

Building the Lötschberg Base Tunnel through the Alps is considered another engineering marvel in Switzerland's transportation network. The Lötschberg line is the first of two major rail corridors designed to shift cross-continental freight traffic from roads to rail. Switzerland invested 26.5 billion USD in both the Lötschberg and Gotthard base tunnels as part of the New Rail Link through the Alps project, which aims to create the first North-South high-speed rail route through the Alps. In the years to come, this will be the only rail line capable of such a feat.

Koralm Tunnel is a rail tunnel currently under construction in Austria, located within the Koralpe mountain range. It is expected to open in 2022. The tunnel will be 32.9 km long, making it the longest railway tunnel in Austria. It will reach depths of up to 1,250 meters below ground. The Koralm Tunnel will consist of two parallel tunnels, each connected by shafts every 500 meters, with an emergency stop planned for the center.

Over 800 workers and three tunnel boring machines have been employed in the construction of the Koralm Tunnel. One of these machines is the first in the world to operate continuously in hard rock for more than 17 kilometers. The Koralm railway line, which links Graz and Klagenfurt, is 90% complete. This 130 km rail route is one of Europe’s most significant transportation infrastructure projects. It forms part of the new southern route and is essential for the Baltic-Adriatic Corridor. The railway will revolutionize travel times between Graz and Klagenfurt, reducing the journey from nearly three hours to just 45 minutes.

Guadarrama Tunnel is a railway tunnel that runs through the Sierra de Guadarrama, along the Madrid - Valladolid high-speed rail route in Spain. The tunnel consists of two tubes, with the western tube measuring 28.407 km and the eastern tube measuring 28.418 km. It is the longest tunnel in Spain and was opened in December 2007. The tunnel is used by the AVE high-speed trains. It is part of a new North-South rail corridor that connects the Meseta region with the northern part of the Iberian Peninsula, crossing the Guadarrama mountain range.

The project includes the construction of lots 3 and 4, which involve two parallel tunnels running from the northern entrance of the route. Lot 3 is 13.3 km long, while Lot 4 is 15.8 km. Designed for speeds of up to 350 km/h, the tunnel meets stringent aerodynamic and comfort standards. The Guadarrama Tunnel is equipped with single-track rails, ventilation, lighting, telecommunication systems, signaling, public address, fire detection and suppression systems, and all necessary safety measures for operation. This project posed significant technical and engineering challenges, and it is now the sixth longest railway tunnel in Europe, the seventh longest in the world, and the second longest in Spain after the Guadarrama Tunnel.

West Qinling Tunnel is part of the railway linking Lanzhou to Chongqing in China, which opened in late 2014. The line is approximately 820 km long, connecting the Gansu province (Lanzhou) to southwestern Chongqing, a city with a population of over 35 million. The tunnel will serve freight transport and connect Longnan city with towns like Waina, Luotang, and Fengxiang in Gansu. Built at a cost of 11.3 billion USD, this new railway will reduce transport time from 17.5 hours to just 6.5 hours and enable an annual freight capacity of around 100 million tons. Trains will travel at speeds of 160 km/h, with up to 50 trains running daily.

In January 2009, China Railway signed a contract with Robbins to supply two 10.2-meter-diameter tunnel boring machines (TBMs) for the construction of the West Qinling Tunnel. The two tunnels, each 16.6 km long, will be dug through the Qinling Mountains. The Robbins TBMs set world-record speeds despite extremely challenging conditions. Despite dealing with high quartz content limestone and difficult geological conditions, only around 100 cutter heads were replaced. By 2013, both machines had completed their final cutting stages.

Taihang Tunnel is the longest railway tunnel through the mountains in China. Located in the Taihang Mountain range, it is also the fifth longest railway tunnel in the world. This double-track tunnel was constructed to allow passengers on the Shitai railway to pass through the Taihang Mountains. The tunnel stretches 27.8 kilometers and was completed on December 22, 2007. Once in operation, the travel time between Shijiazhuang and Taiyuan was reduced from nearly six hours to just one hour.

The Taihang Mountains extend over 400 kilometers from north to south, with elevations ranging from 1,500 meters to 2,000 meters. The twin-tube tunnel was built as part of the Shijiazhuang–Taiyuan railway project to cross this mountain range. The Taihang Tunnel passes through the main slope of the Taihang Mountains, with a maximum overburden of 445 meters. The left tunnel is 27.893 kilometers long, while the right tunnel measures 27.848 kilometers. The distance between the two tunnels is 35 meters. The tunnel was designed by Pöyry.

Cho La Tunnel is approximately 7 kilometers long and is located along the 2,415 km Sichuan-Tibet Highway, which connects Chengdu in eastern Sichuan with Lhasa in western Tibet. Built at an altitude of 4,230 to 4,380 meters above sea level, this tunnel will become the highest tunnel in the world. With a construction period of four years and a total cost of 172 million USD, the tunnel will reduce travel time through the Cho La Mountain pass from over two hours to just 10 minutes. This two-way tunnel, with a speed limit of 40 km/h, cuts through the Cho La Mountains in the Qinghai-Tibet Plateau, covering 7 kilometers with over 5 kilometers of auxiliary roads.

Located in the Cho La mountain range in western Sichuan, China, the Cho La Tunnel is considered one of the highest vehicle tunnels in the world, with an average elevation of 4,378 meters above sea level. Also known as the Que'ershan Tunnel, it passes through the Cho La range. Its surface is paved with asphalt. The tunnel was opened on September 26, 2017, 15 years after the project began, and is situated beneath the Que'ershan Mountain in the Shalulia Range, which rises 6,168 meters above sea level.

The Gotthard Base Tunnel runs beneath the Swiss Alps and is the longest tunnel in the world, stretching approximately 57 kilometers. It surpasses even Japan's Seikan Tunnel, making it the longest tunnel overall. Connecting the Swiss cities of Erstfeld and Bodio, the Gotthard Tunnel consists of two single-track tubes, each dedicated to one railway line. The tunnel is situated as deep as 2.3 kilometers below the mountain peaks, cutting through rocks that reach temperatures of up to 46°C. Engineers had to drill through 73 different types of rock, including some tough granite.

During its construction, more than 28 million tons of rock were removed, and tragically, 9 workers lost their lives. Approximately 2,600 people were involved in the design and construction of this monumental tunnel. The tunnel's traffic control system underwent a major overhaul between 2003 and 2005 by the company Weiss-Electronic GmbH, formerly a subsidiary of SWARCO. As part of the expansion work, the control system was prepared to be integrated into the operational management of the Swiss cantons of Tessin (TI), Nidwalden (NW), and Uri (UR), with a BLE network integration for all traffic computers to follow.

The Brenner Base Tunnel is set to be 55 kilometers long and will traverse the Alps. Connecting Innsbruck Hauptbahnhof in Austria with Franzens Feste (Fortezza) in Italy, this tunnel will replace part of the existing railway line. The Brenner Pass, located in the heart of the Alps between Austria and Italy, is one of the most crucial transport routes between northern and southern Europe. The highway passing through the pass is often plagued by severe traffic congestion, with pollution from traffic being a significant concern. The tunnel is expected to alleviate these issues by significantly improving the rail link between North Tyrol and South Tyrol, drastically reducing travel time through the Alps.

Currently, traffic speeds in the Brenner area rarely exceed 70 km/h due to the steep inclines of existing roads, which pass through the dangerous mountain pass. This project is funded by both Austria and Italy, with additional contributions from the European Union. Once completed, the Brenner Base Tunnel will become the second-longest tunnel in the world, after the Gotthard Tunnel. However, funding to date is still insufficient to meet the estimated costs, with the tunnel expected to be finished by 2025.

Seikan Tunnel is a 53.85 km long railway tunnel in Japan, with approximately 23.3 km of it running beneath the sea floor. Survey work for the tunnel began in 1946, and construction commenced 25 years later in 1971. By August 1982, only about 700 meters of tunnel remained to be dug, and the two sides of the tunnel finally met in 1983. The Tsugaru Strait, where the tunnel passes, is the narrowest at both the eastern and western points, with a width of 20 km. Early surveys conducted in 1946 showed that the eastern sea bed was as deep as 200 meters and consisted primarily of volcanic rock. The western part, being 140 meters deep and made up of Neogene sedimentary rocks, was ultimately chosen for the tunnel's route.

The Seikan Tunnel connects the Japanese island of Honshu with the neighboring island of Hokkaido to the north. It is the second-longest tunnel in the world, after the Gotthard Base Tunnel in Switzerland. The geology under the seabed, which much of the tunnel passes through, consists of fractured volcanic rock, debris, and sedimentary rock. The tunnel's geology can be divided into three sections: volcanic rock (andesite, basalt) on Honshu, sedimentary rock (tuff, Pliocene mudstone) on Hokkaido, and Kuromatsu Nai strata in the middle. The rocks in this area were fragmented and faulted, making excavation extremely difficult, but the tunnel was ultimately completed in 1982.