The world’s longest and deepest undersea road tunnel is being built in Norway, with the aim of reducing travel times between major cities and becoming part of a ferry-free highway along the west coast.
This 27 kilometer long tunnel is called Logfast. It stands for “Rogaland Fastforbinderse,” after the name of the region and the Norwegian word for “fixed link.” At its deepest point, it is 392 meters (1,286 feet) below sea level.
Construction began in January 2018 but was halted at the end of 2019 due to predicted cost overruns, which led to the cancellation of existing contracts and restructuring of the project. Construction will resume at the end of 2021, and the tunnel is currently scheduled to be completed in 2033 at a cost of approximately NOK 25 billion (approximately $2.4 billion).
“This tunnel will significantly improve connectivity along Norway’s west coast by creating a faster and more reliable link between the Stavanger and Haugesund regions,” said Anne-Britt Moen, project manager at multinational construction company Skanska, which is building the northern part of the tunnel, which is 9 kilometers (5.5 miles) long at its deepest point.
Moen added that Logfast’s replacement of the current ferry connection will reduce travel time between Bergen and Stavanger, Norway’s second and fourth most populous cities respectively, by around 40 minutes, making the daily commute much easier.
The tunnel consists of two separate tubes with two lanes designed exclusively for road traffic, and features some rather unusual design elements in about half of the sections. It is a double roundabout with a depth of 260 meters, leading to a connecting tunnel to the island of Hvitzi, Norway’s smallest municipality.
Constructing a tunnel of this length underwater poses several technical challenges. Like most modern tunnels, to save time, Logfast is being built from both ends simultaneously, with the goal of the two construction teams meeting in the center within just 5 centimeters (1.97 inches).
Achieving this level of precision requires careful measurements using lasers and other advanced equipment. A laser scanner with a rotating mirror measures the newly excavated tunnel section, collecting 2 million data points every second to create a “digital twin” of the tunnel. You can then check for inaccuracies against your design plans.
“This is a far cry from the romantic view that surveyors see through their eyepieces,” says Burkhard Bockem, chief technology officer at Hexagon, which provides tunnel measurements.
The 5 centimeter (1.9 inch) margin is one of the tightest in the world, but avoiding mistakes can save you time, money, waste and emissions. “If we deviate from this, we’re going to have to take out a lot of material, and then we’re going to have to refill even more material, which is the equivalent of an entire truck. So this is not only a risk factor, but it’s also a very financial factor.”
technically demanding
The Logfast project is part of the renovation of the E39 coastal highway, a 1,100-kilometer (684-mile) road that runs from Trondheim in the north to Kristiansand in the south. Today, it takes 21 hours to travel the entire length of the road, including seven ferries. The goal is to build tunnels and bridges to eliminate ferries and cut travel times in half. Completion is expected to occur before 2050.
Moen said Logfast was one of the most ambitious and technically demanding components of the plan, and construction was not hurdle-free. “The main challenge so far has been finding a grouting method that is sufficient to seal the rock,” she explained. “We are currently at 300 meters (984 feet) above sea level and have already experienced fairly extensive salt water leaks in our tunnel system. As we descend to 392 meters (1,286 feet) below sea level, we are focused on finding the best way to maintain safe and efficient working conditions for everyone.”
Tunnels also require measures to protect drivers from air pollution. It employs a longitudinal ventilation system (usually using jet fans to create airflow) and is complemented by shaft ventilation extending up to the kvitsoy. “This combination is designed to ensure effective air circulation and safety throughout the considerable length of the tunnel,” Moen said.
Real-time incident alerts will also be implemented to identify events such as breakdowns and traffic jams, and cameras and radar will monitor vehicles.
Mr Moen said that while the closure of the ferry would ultimately result in job losses, the introduction of Logfast would have a positive impact on the local economy and the seafood industry by increasing local communities’ access to other jobs, education and public services, lowering logistics costs and allowing companies to operate over a wider area. “This project will also create substantial jobs during construction and lay the foundations for a more sustainable and integrated regional development along Norway’s fractured west coastline,” she said.
Currently, the title of the world’s longest tunnel with an undersea section, with a total length of 53.85 kilometers (33.5 miles), belongs to the Seikan Tunnel in northern Japan, a railway-only tunnel with an undersea section spanning 23.3 kilometers (14.5 miles).
The Channel Tunnel, which is also a rail-only tunnel connecting England and France, is shorter at 50.46 kilometers (31.35 miles), but its undersea section is longer than Logfast at 37.9 kilometers (23.5 miles). But Logfast is much deeper below sea level than the Seikan Tunnel or the Channel Tunnel, forming its bottom at 240 meters (790 feet) and 115 meters (377 feet) respectively.
