Project Management Institute

Tunnel vision

immense underwater tunnel projects deliver major benefits -- and wrestle with engineering and financial challenges


The Fehmarnbelt Fixed Link tunnel will connect Denmark and Germany.


Underwater tunnels are altering the world map. By joining lands that historically have been connected via lengthy surface routes, these megaprojects can significantly cut down travel times. But with myriad funders, approval agencies and engineering challenges stretching across long schedules, underwater tunnel projects also face a high level of uncertainty.

The Fehmarnbelt Fixed Link tunnel will connect Denmark and Germany. Lying below the Baltic Sea and comprising a twin-track railway and four-lane motorway, the US$10 billion project will reduce travel time from 45 minutes by ferry to seven minutes by train or 10 minutes by car. Rather than the traditional tunnel design of boring below the seabed, the 11-mile (17.7-kilometer) Fehmarnbelt will be built on land and then submerged, becoming the world's longest immersed tunnel when finished in 2024, 13 years after the project launched.


“The Fixed Link will not only benefit the centers of Hamburg and Copenhagen, but also offer opportunities for the regions between both metropolises.”

—Bo Eske Nielsen, Femern A/S, Copenhagen, Denmark

“The Fehmarnbelt Fixed Link realizes the dream of a direct connection between Scandinavia and continental Europe,” says Bo Eske Nielsen, project director, Femern A/S. The Copenhagen, Denmark-based organization is planning and building the tunnel for the Danish government, the project owner. “It will promote the continuous integration of Europe.”

So will the Eurasia Tunnel. When the five-year project is completed in 2017, the Eurasia Tunnel will connect the Asian and European sides of Istanbul, Turkey via a highway running under the Bosporus Strait. The US$1.25 billion, two-story underwater tunnel, 5.4 kilometers (3.4 miles) long, will cut travel time from 100 minutes to 15 minutes. It's not the only tunnel beneath the Bosporus in Turkey's largest city: The Marmaray, a US$4 billion, 13.6-kilometer (8.5-mile) railway, opened in 2013. And the Eurasia Tunnel won't be the last: In early 2015, the government announced a US$3.5 billion, 6.5-kilometer (4-mile) tunnel that will have two levels for cars and a third for trains when it opens in 2020.

“Istanbul is a heavily trafficked city,” says Nigel Hailey, a Birmingham, England-based director for Arup, a technical, environmental and traffic adviser on the Eurasia Tunnel. “There clearly is a demand for cars to cross the Bosporus.”

By improving transportation networks, these underpasses promise to bolster economic networks as well. “The Fixed Link will not only benefit the centers of Hamburg and Copenhagen, but also offer opportunities for the regions between both metropolises,” Mr. Nielsen says.

The nature of these underwater tunnel projects means their project teams must put thorough plans in place, Mr. Hailey says. “It's really about being prepared—and making proper plans if things do go wrong,” he says.

With underwater tunnels, “the big unknown is always ground conditions,” Mr. Hailey says. Poor ground conditions make boring a tunnel difficult, while an environmentally sensitive seabed site discourages an immersed design approach. “You can do lots of ground investigations, digging trial holes, but with a tunnel you're never really quite sure what you're going to find until you get there,” Mr. Hailey says.

The Eurasia Tunnel project team contended with unseen challenges. The initial geotechnical investigation had not been carried out along the exact line of the tunnel, and the tunnel's mechanical and electrical needs had not been fully considered. As a result, the project team had to deepen the alignment and increase the size of the tunnel diameter. It also planned extensively for emergency situations, installing an exit route between the upper and lower decks and creating a ventilation system that minimizes the spread of smoke.

Because of such comprehensive preparations, when these initiatives finally get the green light from funders and government agencies, they can very quickly move into the execution phase. Because the Danish Parliament authorized Femern A/S to conduct limited advanced activities on the Danish side, the project team was able to begin preparations for the seaside factory that will build the tunnel while still negotiating bids with potential contractors.

Given the projects’ large budgets and correspondingly high cost of delays, their owners often depend on public-private partnerships (PPP) to take the financial risk off the funders and place it onto the contractors. With the Eurasia Tunnel, costs associated with running over budget and schedule fall to the private-sector special purpose organization that's constructing it; conversely, if that organization finds savings, it keeps them.

In Miami, Florida, USA, the US$1 billion PortMiami tunnel was scheduled to open in May 2014 after four years of construction, but project closure was delayed by three months while engineers corrected last-minute glitches including faulty exhaust fans and a leaky drainage pipe. The project's PPP structure incentivized speedy resolutions: The contractor paid Miami's government US$9 million for the delays.

“You don't let the contractor leave until everything's perfect,” Chris Hodgkins, vice president of MAT Concessionaire, the consortium that built the tunnel, told the Miami Herald. —Novid Parsi

The Eurasia Tunnel will connect the Asian and European sides of Istanbul, Turkey. The US$1.25 billion, two-story underwater tunnel, will cut travel time from 100 minutes to 15 minutes.


Projects that seem fantastic today could be a reality tomorrow. Here are a few of the more far-fetched tunnels proposed in recent years.

  • U.K. to Ireland: A Welsh think tank has discussed an underwater rail tunnel from Ireland to the United Kingdom. The Chartered Institute of Logistics and Transport Cymru-Wales estimates a tunnel linking the cities of Holyhead, Wales to Dublin, Ireland would cost £15 billion and could be finished by the end of the century.
  • China to the United States: Chinese officials are reportedly considering a rail link from Beijing, China to Alaska, USA. The 8,000-mile (12,875-kilometer) path would travel north through Siberia before tunneling under the Bering Strait.
  • Dalian, China to Yantai, China: At 123 kilometers (76 miles) in length, this US$36 billion tunnel would be the world's longest underwater tunnel if completed. Connecting the cities of Dalian and Yantai across the Bohai Sea, the tunnel's high-speed rail line would slash travel time from eight hours by ferry to just 40 minutes. A government feasibility study is reportedly underway.
  • Japan to South Korea: Proposals for a 200-kilometer (124-mile) undersea tunnel have been around since 1917, with one suggested route linking Karatsu, Japan to Geoje Island, Korea. But in 2011, the Korean government said projected costs—KRW100 trillion—for several tunnels made them economically unfeasible.
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