Norway is building the longest and deepest undersea road tunnel in the world

The longest and deepest car tunnel in the world is being constructed in Norway, under the surface of the sea, with the aim of reducing travel time between major cities and becoming part of a highway extending along the western coast of the country without the need to use ferries. The length of the tunnel is 27 kilometers, and it is called “Rogfast”, which is an abbreviation of the phrase “Rogaland fastforbindelse”, derived from the name of the region in which the tunnel is located, and the Norwegian word means “fixed link”.

At its deepest point, the tunnel will reach 392 meters below sea level. Construction work began in January 2018, but was halted in late 2019 due to expectations of exceeding specified costs, which led to the cancellation of existing contracts and the restructuring of the project.

Work resumed in late 2021, and the tunnel is currently scheduled to be completed in 2033, at an estimated cost of approximately 2.4 billion US dollars. “The tunnel will contribute significantly to improving connectivity between areas of the west coast of Norway, by providing a faster and more reliable route between the regions of Stavanger and Haugesund,” said Anne-Britt Moen, project manager at Skanska, the multinational construction company implementing the northern part of the tunnel, which is the deepest part and extends for 9 kilometers.

Moen added that the “Rogfast” tunnel, which will replace the current ferry lines, will reduce travel time between the cities of Bergen and Stavanger, which are the second and fourth largest cities in Norway in terms of population, respectively, by about 40 minutes, and will also make daily transportation between the regions easier. The tunnel will consist of two separate tubes, each containing two traffic lanes, and will be designated exclusively for vehicles.

It will include an unusual engineering design at approximately its midpoint, which is represented by a double roundabout located at a depth of 260 meters, and connected to a sub-tunnel leading to Kvitsøy Island, which is the smallest municipality in Norway. Measurements using advanced techniques Constructing a tunnel of this length under the sea presents many technological challenges.

Like most modern tunnels, excavation work in the Rogfast Tunnel is carried out from both ends at the same time to save time, with the two construction teams meeting in the middle with a margin of error not exceeding 5 centimetres. Achieving this level of accuracy requires extremely precise measurements using lasers and other advanced equipment.

A laser scanner equipped with a rotating mirror is used to scan the newly excavated sections of the tunnel, collecting two million data points per second to create a “digital twin” of the tunnel, which can then be compared with engineering drawings to detect any discrepancies or errors. “We've moved away a bit from the traditional, romantic image of a surveyor looking through the lens of a measuring device,” said Burkhard Boeckem, chief technology officer at Hexagon, which provides the measurement technology used in the project.

The 5cm margin of error is one of the most stringent accuracy standards in the world, but it contributes to saving time and money and reducing waste and emissions by avoiding errors. “If you exceed this margin, you will produce much larger quantities of material that must be taken out, and then you will need large additional quantities to fill the spaces again, which is equivalent to a large number of truckloads,” Boekeem explained.

“Therefore, it is not only a matter of risk factors, but it also has a significant financial impact.” Complex technical challenges The Rogfast project is part of a comprehensive plan to develop the E39 coastal highway, which extends 1,100 kilometers from the city of Trondheim in the north to Kristiansand in the south.

It currently takes about 21 hours to cover the entire route by car, including the use of seven sea ferries. The plan aims to dispense with ferries by constructing new tunnels and bridges, which would reduce the journey time by half.

The entire project is not expected to be completed before 2050. The Rogfast Tunnel is one of the most ambitious and technically complex components of this plan.

According to Moen, construction work was not without obstacles. “The main challenge so far has been finding methods suitable enough to inject the rock with insulating materials to fill the cracks and prevent water leakage,” she explained.

She added: “We have now reached a depth of 300 meters below sea level, and we have already encountered relatively large salt water leaks within the tunnel network. Given that we will continue digging to a depth of 392 meters below sea level, we are focusing on finding the best ways to maintain safe and efficient working conditions for everyone.”

The tunnel also requires measures to protect drivers from air pollution. It will be equipped with a longitudinal ventilation system, which usually relies on jet fans to generate air flow, in addition to a ventilation system through vertical openings extending to Kvitsoe Island.

Moen explained that this integrated system “was designed to ensure effective air circulation and maintain safety throughout the tunnel, given its great length.” An immediate warning system will also be implemented to monitor accidents and traffic problems, such as vehicle breakdowns or congestion, in addition to using cameras and radar devices to monitor vehicle movement.

Although the closure of ferry lines will ultimately lead to the loss of some jobs, Moen stressed that the “Rogfast” project will enhance access to other jobs, as well as facilitate access to educational institutions and public services for local communities. She added that the project will have a positive impact on the local economy and the seafood sector, as logistics costs will decrease, and companies will be able to expand their operations to larger geographical areas.

She said: “The project also provides great job opportunities during the construction phase, and lays the foundation for a more sustainable and integrated regional development along the western coast of Norway, which is interspersed with fjords and separated by many areas of water.” Currently, the Seikan Tunnel in northern Japan holds the title of the longest tunnel in the world that includes an undersea section.

This tunnel is designated for train traffic only, and its total length is 53.85 kilometers, of which 23.3 kilometers are under sea level. As for the “Manche Tunnel,” which is also called the “Channel Tunnel,” which connects England to France and is also used for trains only, its total length is 50.46 kilometers, meaning that it is shorter than the Sican Tunnel, but the section extending under the sea in it is 37.9 kilometers, which is longer than the “Rogfast” tunnel.

However, the "Rogfast" tunnel will be much deeper below sea level than both the "Seikan" and the Channel tunnels, with their maximum depths reaching 240 meters and 115 meters respectively, compared to the 392 meters depth of the "Rogfast" tunnel.