Intercontinental and transoceanic fixed links

Cosmopolitan Railway

In 1890 William Gilpin first proposed to connect the continents by land via the Cosmopolitan Railway. Significant elements of that proposal, such as the English Channel Tunnel, have been constructed since that era. However, the improvement of the global shipping industry and advent of international air travel has reduced the demand for many intercontinental land connections.

Trans Global Highway

The Trans-Global Highway is a range of proposed highway systems that would link all six of the inhabited continents on Earth and was proposed by Frank X. Didik. If constructed, cars could drive from Australia to California via Russia and Alaska. People from New York would also be able to drive to London via Greenland. The highway would network new and existing bridges and tunnels, improving not only ground transportation but also potentially offering a conduit for utility pipelines. However, in Discovery Channel's Extreme Engineering, it was noted the Chukotka area is mostly roadless and uninhabited, and infrastructure would need to be developed completely from scratch. Chukotka lies on the Eurasian side of the Bering Strait, where the highway would connect to North America via tunnels.

English Channel

There is no highway connection between Great Britain and the European mainland; only a railway connection, the Channel tunnel.

A cross channel rail tunnel was first proposed in 1802 and construction actually started in 1881 before being abandoned. Roll-on Roll-off ferry services provided links across the channel for vehicles.

A road tunnel was proposed in 1979, but not considered viable. Construction of the Channel Tunnel started in 1988 and the tunnel opened in 1994. Automobiles and lorries/transport trucks are loaded onto the Eurotunnel Shuttle's enclosed railway cars (similar to auto rack/motorail railway cars) for the trip through the tunnel, however. A service tunnel runs the entire length of the crossing, but is closed to general use and used only during emergencies and for maintenance.

Irish Sea

Various ferry services link Ireland to Britain and France. A number of options for an Irish Sea fixed crossing have been proposed over the years but none are currently under serious consideration.

Germany to Denmark to Sweden

The Øresund Bridge links southern Sweden to the Danish island of Zealand. Zealand is linked to the Danish mainland and the rest of Europe by the Great Belt Fixed Link. Most travellers between Sweden and Germany, both by road and train use the 160 km (100 mi) shorter route with a ferry over the Fehmarn Belt southwestwards towards Hamburg or southwards to Rostock. A Fehmarn Belt Fixed Link is planned to be opened in 2021. A Gedser-Rostock Bridge is also under consideration.

Sweden to Finland

Ferry services link Sweden to Finland via the Åland Islands. There are proposals of fixed links between Sweden and Finland. A tunnel could be built between Sweden and Åland, around 50 km length, and 100–200 meters depth, with the lowest depth around Märket, a little detour. The area between Åland and Finland is shallow with many islands, able to be connected with bridges. Between Umeå and Vaasa further north, there is a proposal to build the Kvarken Bridge, a series of bridges, the longest 26 km, in total 40 km. None of these proposals have been seriously investigated.

Finland to Estonia

Ferry Services link Finland to Estonia as well as overground rail and road routes via Saint Petersburg in Russia. Rail Baltica is a proposal for a rail link from Finland to Estonia, Latvia, Lithuania and Poland, bypassing Russia via a Helsinki to Tallinn Tunnel.

Italian mainland to Sicily

The Strait of Messina has a busy ferry traffic. The Strait of Messina Bridge is planned, but the construction date has been postponed several times.

Gibraltar Tunnel

The Gibraltar Tunnel is proposed to be a rail tunnel linking Africa and Europe. Due to the depth of the Strait of Gibraltar (300–900 metres / 1000–2950 feet), it would be a great challenge to remove automobile exhaust from this depth. Any tunnel would most likely be an electrified rail tunnel, similar to the Channel Tunnel linking the UK and France. There have also been proposals for a bridge over the Strait. There are car ferries across the strait.

Strait of Sicily

The proposed Strait of Sicily Tunnel would link Sicily to Tunisia. Together with the proposed Strait of Messina Bridge from Sicily to Italy this would provide a fixed link between Italy and Tunisia.

The Bosphorus

The Turkish Straits are the channel between European Turkey and Asian Turkey and consist of the (from south to north) Dardanelles the Sea of Marmara and the Bosphorus

The waters of the strait are traversed by numerous ferries. Two suspension bridges cross the Bosphorus. The first of these, the Bosphorus Bridge, is 1,074 m (3,524 ft) long and was completed in 1973. The second, named Fatih Sultan Mehmet (Bosporus II) Bridge, is 1,090 m (3,576 ft) long, and was completed in 1988 about 5 km (3 mi) north of the first bridge. The Bosporus Bridge forms part of the O1 Motorway, while the Fatih Sultan Mehmet Bridge forms part of the Trans-European Motorway.

Construction of a third suspension bridge, the Yavuz Sultan Selim Bridge, began on May 29, 2013; it was opened to traffic on August 26, 2016. The bridge was built near the northern end of the Bosporus, between the villages of Garipçe on the European side and Poyrazköy on the Asian side. It is part of the "Northern Marmara Motorway", which will be further integrated with the existing Black Sea Coastal Highway, and will allow transit traffic to bypass city traffic.

The Marmaray project, featuring a 13.7 km (8.5 mi) long undersea railway tunnel, opened on 29 October 2013. Approximately 1,400 m (4,593 ft) of the tunnel runs under the strait, at a depth of about 55 m (180 ft).

An undersea water supply tunnel with a length of 5,551 m (18,212 ft), named the Bosporus Water Tunnel, was constructed in 2012 to transfer water from the Melen Creek in Düzce Province (to the east of the Bosporus strait, in northwestern Anatolia) to the European side of Istanbul, a distance of 185 km (115 mi).

The Eurasia Tunnel is a road tunnel between Kazlicesme and Goztepe, which began construction in February 2011 and is opened to traffic on 21 December 2016.

Saudi-Egypt Causeway

The Saudi-Egypt Causeway is a proposal for a causeway and bridge between the Sinai Peninsula in Egypt and the northern part of Saudi Arabia. This would provide a direct road route between Egypt and Saudi Arabia without going through Israel or Jordan. There is a car ferry between Safaga, Egypt and Duba, Saudi Arabia.

Bridge of the Horns

The Bridge of the Horns is a proposed construction project to build a bridge between the coasts of Djibouti and Yemen across the Bab-el-Mandeb, the strait between the Red Sea and Gulf of Aden. There is no ferry today (2016).

Sri Lanka

The Boat Mail train and ferry service provided a train and ferry service from India to Sri Lanka until the First World War. An India–Sri Lanka HVDC Interconnection is under consideration to link the electricity networks of these countries.

South East Asian islands

Mainland Peninsular Malaysia is linked to Penang Island by two road bridges: the Penang Bridge and the Sultan Abdul Halim Muadzam Shah Bridge (Penang Second Bridge). To the south, it is linked to Singapore Island across the Straits of Johor by the Johor–Singapore Causeway and the Malaysia–Singapore Second Link; the former also carries Malaysia's West Coast Line to the island.

Passenger and vehicle ferries link the various islands of Indonesia, Malaysia, Singapore, the Philippines and Papua New Guinea.

There are proposals to link Java, the most populated Island of Indonesia to Sumatra via a proposed Sunda Strait Bridge and from Sumatra to Singapore and/or Malaysia via a Malacca Strait Bridge.

Australia-Papua New Guinea Tunnel

A tunnel/bridge between the Australian mainland and the island of New Guinea, bridging the Torres Strait, is not considered economically feasible owing to the great distance. Cape York in northern Queensland is 140 km away from New Guinea. This is a very long distance compared to existing tunnels or bridges, and the demand for car travel is not so high; as of 2009 there are no car ferries between Australia and Papua New Guinea. Passenger travel is by air only.

Hainan Island

The Guangdong–Hainan Ferry, or the Yuehai Ferry (part of the Guangdong–Hainan Railway) is a vehicle and Train ferry connecting Hainan Island to Guangdong in mainland China. The ferries run across the Qiongzhou Strait, between Zhanjiang, Guangdong and Haikou, Hainan.

Taiwan

The Taiwan Strait Tunnel Project is a proposed undersea tunnel to connect Pingtan in China to Hsinchu in northern Taiwan as part of the G3 Beijing–Taipei Expressway. First proposed in 1996, the project has since been subject to a number of academic discussions and feasibility studies, including by the China Railway Engineering Corporation. There exist cross strait ferries, both within outlying island of Taiwan and between PRC and Taiwan.

South Korea

Since the Korean War travel overland from South Korea through North Korea to China and Russia has been blocked. South Korea maintains ferry services to Japan and China.

Korea to Japan

The "Korea Japan Friendship Tunnel System," is a proposal for a fixed link from the city of Fukuoka on Kyūshū, Japan, to the port city of Busan in Korea via four islands. The maximum ocean depth in this area is 146 m (480 feet). Similar proposals have been discussed for decades by Korean and Japanese politicians. A road bridge links Kyūshū to the main Japanese island of Honshu.

Japan to Russia

The Seikan Tunnel has provided a rail link from the main Japanese Island of Honshu to the northernmost Japanese island of Hokkaido since 1988. The proposed Sakhalin-Hokkaido Tunnel would link Hokkaido to the Russian island of Sakhalin. When combined with the proposed Sakhalin Tunnel between Sakhalin and the Russian Mainland and an extension of the Baikal Amur Mainline this would give a rail link from Japan to Russia and the mainland of Asia.

Bering Strait bridge or tunnel

There is a proposal is to span the Bering Sea with a bridge or tunnel called the Intercontinental Peace Bridge, the TKM-World Link or the AmerAsian Peace Tunnel. This would link the American Cape Prince of Wales, with the Russian Cape Dezhnev. The Bering Strait Tunnel would consist of 3 tunnels connecting Alaska and Russia by going through two islands (the Little Diomede (USA) and Big Diomede (Russia)). The longest single tunnel would be 24 miles (40 km). Since the Bering Sea at the proposed crossing has a maximum known depth of 170 feet (50 m), the tunnels might be dug with conventional tunnel boring machines of the type that was employed in the construction of the Channel Tunnel. The three tunnel proposal is considered to be preferable over a bridge due to severe environmental conditions, especially the inescapable winter ice damage.

Each proposed tunnel would be shorter than some current tunnels. The Channel tunnel linking England with mainland Europe is approximately 31.34 miles (50.45 km) long; the ocean tunnel Seikan linking Hokkaidō with Honshū in Japan is 33.46 miles (55.86 km) long; and the Swiss Gotthard Base Tunnel through the Alps, currently under construction, will be 35.7 miles (59.60 km) long.

To make a bridge or tunnel useful, a road or railway must be built to connect it, despite very difficult climate and very sparse population that makes roads less economically motivated. In Alaska a 700 mile (1,100 km) link would be needed, and in Russia a link more than 1,200 miles (2,000 km) long must be constructed. Until around 2010 such road connections were suggested by enthusiasts only, but at that time both the Russian government and the Alaskan state government started considering such roads.

Vancouver Island

Ferry services link Vancouver Island to British Columbia on the Canadian Mainland and to the State of Washington in the US.

Proposals have been made for a fixed link to Vancouver Island for over a century. Because of the extreme depth and soft seabed of the Georgia Strait, and the potential for seismic activity, a bridge or tunnel would face monumental engineering, safety, and environmental challenges at a prohibitive cost.

Prince Edward Island

Prince Edward Island is linked to New Brunswick on the Canadian mainland by the Confederation Bridge which opened in 1997.

Newfoundland

Various proposals have been considered for a fixed link consisting of bridges, tunnels, and/or causeways across the Strait of Belle Isle, connecting the province of Newfoundland and Labrador's mainland Labrador region with the island of Newfoundland. This strait has a minimum width of 17.4 km (10.8 mi).

Long Island

Nine bridges and 13 tunnels (including railroad tunnels) connect Brooklyn and Queens, on Long Island, to Manhattan Island and Staten Island and, via these, to Newark in New Jersey and The Bronx on the mainland of New York state. Ferries connect Suffolk County northward across Long Island Sound to the mainland of New York state and westward to the state of Connecticut. There have been various proposals for a fixed link across Long Island Sound to replace these ferries.

Delmarva

The Chesapeake Bay Bridge–Tunnel (CBBT) is a 23-mile-long (37 km) fixed link crossing the mouth of the United States' Chesapeake Bay, connecting the Delmarva Peninsula with Virginia Beach, Virginia. It opened in 1964.

Florida to Puerto Rico

Ferry services between the US and Cuba and between Cuba and Haiti have been suspended due to the ongoing United States embargo against Cuba.

There's only one regular ferry to Havana from a foreign port: Cancún, Mexico.

There is a ferry that travels between Mayagüez in Puerto Rico and Santo Domingo in the Dominican Republic.

Darién Gap

A notable break in the Pan-American Highway is a section of land located in the Darién Province in Panama and the Colombian border called the Darién Gap. It is an 87-kilometre (54 mi) stretch of rainforest. The gap has been crossed by adventurers on bicycle, motorcycle, all-terrain vehicle, and foot, dealing with jungle, swamp, insects, kidnapping and other hazards.

Some people, groups, indigenous populations, and governments are opposed to completing the Darién portion of the highway. Reasons for opposition include protecting the rain forest, containing the spread of tropical diseases, protecting the livelihood of indigenous peoples in the area, and reducing the spread of drug trafficking and its associated violence from Colombia.

Transatlantic tunnel

A transatlantic tunnel is a theoretical tunnel that would span the Atlantic Ocean between North America and Europe possibly for such purposes as mass transit. Some proposals envision technologically advanced trains reaching speeds of 500 to 8,000 kilometres per hour (310 to 4,970 mph). Most conceptions of the tunnel envision it between the United States and the United Kingdom ‒ or more specifically between New York City and London.

Advantages compared to air travel could be increased speed, and use of electricity instead of scarce oil based fuel, considering a future time long after peak oil.

The main barriers to constructing such a tunnel are cost with estimates of between $175 billion to $12 trillion as well as the limits of current materials science. Existing major tunnels, such as the Channel Tunnel, Seikan Tunnel and the Gotthard Base Tunnel, despite using less expensive technology than any yet proposed for the transatlantic tunnel, struggle financially.