Norway is building the world’s deepest and longest road tunnel nearly 400 metres below the sea

Norway is going on with a massive transport project that, while mostly invisible to the public, is significant in scope. Deep beneath the North Sea, work is continuing on Rogfast, an undersea road tunnel that will be part of a ferry-free route along the country's western coastline. The tunnel is already being cut through solid rock and will eventually span over 27 kilometres, reaching depths of nearly 400 meters below sea level. Once completed, it is planned to cut travel times between major cities and lessen dependency on weather-prone ferry crossings. CNN, which has closely monitored the tunnel's progress, has reported on the project's technical requirements and lengthy schedule. The project also showcases Norway’s engineering ambition, safety standards, environmental planning, and long-term infrastructure investment priorities for future generations nationwide.Rogfast is short for Rogaland fastforbindelse, named after the region it serves and the Norwegian term for a fixed link. The tunnel will connect Randaberg and Bokn, forming part of the E39 coastal highway. This road runs for more than 1,100 kilometres from Trondheim in the north to Kristiansand in the south. Today, drivers must board seven ferries to complete the journey. The long-term plan is to remove those crossings through a mix of tunnels and bridges. Rogfast is one of the most complex sections of that plan and also one of the first to take shape underground.At its deepest point, Rogfast will be approximately 392 metres below sea level. This makes it significantly deeper than existing submarine tunnels used for automotive or rail transportation. According to CNN, engineers are excavating the tunnel from both ends at the same time, with teams operating in tandem beneath the seabed. The goal is to achieve an error margin of fewer than five cm. This level of accuracy saves money and prevents costly mistakes, especially given the amount of rock being removed.Precision work at this depth relies heavily on measurement technology. As reported by CNN, laser scanners are used to record newly excavated sections of the tunnel, capturing millions of data points every second. These measurements create a digital model that is compared against design plans. Burkhard Boeckem, chief technology officer at Hexagon, the company providing the measurement systems, told CNN that even small deviations can lead to large increases in material handling. Correcting mistakes underground often means removing more rock and then reinforcing the structure again, which adds time and cost.Working hundreds of metres below sea level brings constant pressure from the surrounding rock and seawater. One of the main technical challenges has been sealing cracks in the rock to prevent saltwater from leaking into the tunnel. Anne Brit Moen, a project manager at Skanska, which is building the northern section of Rogfast, told CNN that water ingress has already occurred during excavation. She said the team is focused on improving grouting methods to maintain safe working conditions as the tunnel goes deeper. The northern section alone is about nine kilometres long and includes the deepest parts of the route.Rogfast will consist of two separate tubes, each carrying two lanes of traffic. About halfway along the tunnel, drivers will pass through a double roundabout located roughly 260 metres below sea level. This underground junction connects to a branch tunnel leading to the island of Kvitsøy, Norway’s smallest municipality. Air quality inside the tunnel is another priority. The design includes a longitudinal ventilation system supported by ventilation shafts. CNN reports that real-time monitoring systems, cameras and radar will also be used to detect incidents and manage traffic flow.Rogfast's construction commenced in 2018, but it was suspended in 2019 as a result of anticipated cost overruns. Work resumed in 2021 following the restructuring, and completion is now anticipated for 2033. The estimated cost is approximately 25 billion Norwegian kroner, which is equivalent to approximately 2.4 billion US dollars. Moen stated to CNN that enhanced road access will support other forms of employment, education, and public services, despite the likely decline in ferry jobs over time. Additionally, industries such as marine processing are anticipated to benefit from reduced transportation expenses. The tunnel is expected to have a gradual impact, altering daily routines rather than causing an abrupt change.