A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ventilation openings at various points along the length. A pipeline differs significantly from a tunnel, though some recent tunnels have used immersed tube construction techniques rather than traditional tunnel boring methods.
A Bering Strait crossing is a hypothetical bridge or tunnel that would span the relatively narrow and shallow Bering Strait between the Chukotka Peninsula in Russia and the Seward Peninsula in the U.S. state of Alaska. The crossing would provide a connection linking the Americas and Afro-Eurasia.
The Hokkaido Shinkansen is a Japanese high-speed Shinkansen rail line that links up with the Tōhoku Shinkansen in northern Aomori Prefecture in Honshu and continues on into the interior of Hokkaido through the undersea Seikan Tunnel. Construction started in May 2005; the initial Shin-Aomori to Shin-Hakodate-Hokuto section opened on 26 March 2016. The section of the line to Sapporo is scheduled to open by fiscal year 2030. The line is operated by the Hokkaido Railway Company.
The Fehmarn Belt fixed link or Fehmarn Belt tunnel is an under-construction immersed tunnel, which will connect the Danish island of Lolland with the German island of Fehmarn, crossing the 18-kilometre-wide (11 mi) Fehmarn Belt in the Baltic Sea.
The Stockholm Ring Road is a half-completed ring road around central Stockholm, Sweden. There have been many plans over the years of a ring road around central Stockholm, but all of them have been cancelled at some point. As of 2015, three quarters of the ring road have been built.
Several future projects on the MTR have been put forward by the MTR Corporation to the Hong Kong Government. Some of these are still in planning stage.
Nuclear power plants operate in 32 countries and generate about a tenth of the world's electricity. Most are in Europe, North America and East Asia. The United States is the largest producer of nuclear power, while France has the largest share of electricity generated by nuclear power, at about 70%.
Long Thanh International Airport is an international airport under construction in Long Thành district, Đồng Nai province, Vietnam, approximately 40 km (25 mi) east of Ho Chi Minh City. It will be the second airport to serve the Ho Chi Minh City metropolitan area, after the existing Tan Son Nhat International Airport. It is being built as an alternative to the existing airport, in order to relieve its increasing traffic, demand and congestion, as it could not be further expanded due to urban growth around it. The Government of Vietnam approved its construction on 4 January 2021. Construction began the next day on 5 January, and its first phase was scheduled to be finished by September 2025, but now it is expected to be finished by the first half of 2026. The airport will serve over 100 million passengers and five million tonnes of cargo annually when built to the maximum designed capacity, making it the largest airport in Vietnam, Southeast Asia and one of the largest in the world. The project is the most expensive infrastructure project in Vietnam's history. Once open, both airports will operate together. The national carrier, Vietnam Airlines, is suggested by the project consultants as the only Vietnamese carrier to operate flights from Long Thanh, while other airlines will wholly stay at the existing airport.
High-speed rail in Italy consists of two lines connecting most of the country's major cities. The first line connects Turin to Salerno via Milan, Bologna, Florence, Rome and Naples, the second runs from Turin to Venice via Milan and Verona, and is under construction in parts. Trains are operated with a top speed of 300 km/h (190 mph).
The Zimmerberg Base Tunnel (ZBT) is a railway tunnel under the Zimmerberg mountains in Switzerland. Phase I of the tunnel was opened to traffic during April 2003.
Förbifart Stockholm is a series of underground motorway tunnels currently under construction between the Kungens Kurva interchange in the south of Stockholm and the Häggvik interchange north of Stockholm. Most of this bypass, more than 17 out of 21 kilometres, is being built underground. The Swedish government decided to permit the construction of the bypass on 3 September 2009, according to a proposal by the Swedish Road Administration.
The West Link is an underground railway tunnel under construction in Gothenburg, Sweden, that includes three new underground stations: Centralen, Haga and Korsvägen. The purpose of the project is to increase capacity and reduce travel times.
The North–South express railway is a planned high speed railway in Vietnam. The line would begin in Thanh Trì and end in Thủ Đức, connecting the two most urbanised areas in the country: Hanoi in the North, and Ho Chi Minh City in the South. This project is part of the country's railway transport development strategy by 2020 with a vision to 2050. The project is also part of the Trans-Asian railway network. Vietnam’s National Assembly approved the $67 billion railway in November 2024.
The City Rail Link (CRL) is a rail project currently under construction in Auckland, New Zealand. The project consists of a 3.5 km (2.2 mi) long double-track rail tunnel underneath Auckland's city centre, between Waitematā (Britomart) and Maungawhau railway stations. Two new underground stations will be constructed to serve the city centre: Te Waihorotiu near Aotea Square and Karanga-a-Hape near Karangahape Road. Waitematā will be converted from a terminus station into a through station, and Mount Eden station will be replaced by Maungawhau station, a new station with four platforms to serve as an interchange between the new CRL line and the existing Western Line.
The Kuragino-Kyzyl railway line is an unfinished railway construction project in Tuva, Russia. The railway was estimated to be 411.7 kilometres long and will link Tuva with Krasnoyarsk Krai and railway network of Russia.
The Semmering Base Tunnel is a railway tunnel under construction between Gloggnitz and Mürzzuschlag in Austria underneath the Semmering Pass. The existing route is 41 km long and the Semmering Base Tunnel will be 27.3 km long. The new route will offer time savings of up to 30 minutes, partly on account of the shorter route and partly on account of the higher speed limit.
Zoji La Tunnel is an under-construction 9.5 m wide, 7.57 m high and 14.2 km long, horseshoe-shaped single-tube, 2 lane road tunnel at the height of 11,575 feet above sea level which passes under the Zoji La pass in the Himalayas between Ganderbal of Kashmir (J&K) and Drass town in Kargil district of Ladakh. The project cost for this smart tunnel (SCADA) system, constructed using the New Austrian tunneling method and equipped with CCTV, radio control, uninterrupted power supply, ventilation, etc is INR 8,308 crore as per 2021 estimates. Together with the adjacent Z-Morh Tunnel, this geostrategically important tunnel on the NH1 Srinagar-Leh Highway will provide year around weather-proof connectivity to Ladakh and Baltal, reduce the earlier 1-1.5 hours travel time to just 15 minutes drive, boost the tourism and economy, and enhance the logistics of the Indian Armed Forces. It is one of the 31 road tunnels being constructed at a combined cost of INR1400 billion.
The Pink Line of Namma Metro is under construction and will form part of the metro rail network for the city of Bangalore, Karnataka, India. The 21.25 km (13.20 mi) line connects Kalena Agrahara station on Bannerghatta Road in the south with Nagawara station on Outer Ring Road in the north. The Pink Line is mostly underground but also has a 6.98 km (4.34 mi) elevated section and a 0.48 km (0.30 mi) at-grade (surface) section. There are 18 stations on the line, including 12 underground and 6 elevated ones. Pink Line will have an interchange with the Purple Line at MG Road station. It will also have interchanges with the Yellow line at Jayadeva Hospital station and with the Blue Line at Nagawara. Both these lines are under construction.
Karanga-a-Hape railway station is an underground railway station under construction in Auckland, New Zealand. It is scheduled to open in 2026 as part of the City Rail Link project. It will serve the Karangahape Road area with entrances on Beresford Square and Mercury Lane. When it opens, Karanga-a-hape will be the deepest train station in New Zealand, reaching 33 metres down and featuring 150 metre long platforms. Auckland Council estimates up to 1,400 people an hour will use the station at peak times.