The world’s longest and deepest subsea road tunnel is currently under construction in Norway, intended to slash travel times between major cities and become part of a ferry-free motorway along the western coast.
Measuring 27 kilometers (17 miles) in length, the tunnel is named Rogfast, an abbreviation derived from “Rogaland fastforbindelse”—referencing the region where it is situated and a Norwegian term meaning “fixed link.” At its deepest points, it will lie 392 meters (1,286 feet) beneath sea level.
Construction commenced in January 2018 but faced a halt near the end of 2019 due to projected cost overruns, leading to the cancellation of existing contracts and a project redesign. Work resumed in late 2021, with the tunnel completion now anticipated in 2033 at an estimated cost of around 25 billion Norwegian kroner (approximately $2.4 billion).
“The tunnel will dramatically improve connectivity along Norway’s west coast, establishing a quicker and more reliable link between the Stavanger and Haugesund regions,” stated Anne Brit Moen, Project Manager at Skanska, the multinational construction firm responsible for the northern segment of the tunnel—the deepest section, spanning 9 kilometers (5.5 miles).
By replacing current ferry services, Rogfast will reduce the journey time between Bergen and Stavanger—Norway’s second and fourth most populous cities, respectively—by roughly 40 minutes and significantly ease daily commuting, Moen added.
The tunnel will feature two separate bores, each equipped with two lanes dedicated exclusively to vehicle traffic. It will incorporate a rather unique structural feature roughly midway: a 260-meter deep double-roundabout leading to a connecting tunnel that accesses the island of Kvitsøy, Norway’s smallest municipality.
High-Tech Measurements
Constructing a tunnel of this magnitude underwater presents numerous engineering challenges. Like most modern tunnels, Rogfast is being excavated simultaneously from both ends to save time, with the two construction crews aiming to meet in the middle with an error margin of only 5 centimeters (1.97 inches).
Achieving this level of precision demands meticulous surveying utilizing lasers and sophisticated equipment. A rotating mirror laser scanner surveys the newly excavated tunnel section, capturing 2 million data points per second to generate a “digital twin” of the tunnel. This digital model can then be checked against the design blueprints for any inaccuracies.
Laser measurement equipment is used to ensure the two ends meet in the middle accurately.
Laser measurement equipment is used to ensure the two ends meet in the middle accurately. Skanska
“It’s a little bit away from the romantic view of the of the surveyor looking through an eyepiece,” commented Burkhard Boeckem, Chief Technology Officer at Hexagon, the company supplying the measurements for the tunnel.
The 5-centimeter (1.9-inch) tolerance is among the world’s tightest specifications, yet adherence saves resources—time, money, materials, and emissions—by preventing errors: “If you deviate from this, you create so much more material that needs to be taken out, and then so much more to be filled in again — it’s a lot of whole trucks. So, it’s not just a risk factor, but also a very financial factor.”
Technically Demanding
The Rogfast project constitutes a major part of the upgrade for the E39 coastal highway, a 1,100 kilometer (684-mile) road stretching from Trondheim in the north down to Kristiansand in the south. Current travel along this route takes 21 hours and involves traversing seven ferries. The long-term objective is to eliminate all ferries by constructing tunnels and bridges, aiming to cut the total travel time in half. Completion for the entire E39 upgrade is not anticipated before 2050.
Rogfast stands out as one of the most ambitious and technically challenging components of that overall plan, and construction has not been without obstacles, according to Moen. “The main challenge so far has been to find good enough grouting methods to seal the rock,” she clarified. “We are now 300 meters (984 feet) below sea level, and we have already had quite extensive saltwater leaks in the tunnel system. Since we are going all the way down to 392 meters (1,286 feet) below sea level, we’re focusing on finding the best methods to maintain safe and efficient working conditions for everyone.”
“Measurement While Drilling” data is used to analyze and visualize the geological conditions along the tunnel.
“Measurement While Drilling” data is used to analyze and visualize the geological conditions along the tunnel. Skanska
The tunnel also necessitates measures to safeguard drivers from air pollution. It will feature a longitudinal ventilation system—which typically employs jet fans to generate airflow—supplemented by shaft ventilation extending up to Kvitsøy. “This combination is designed to ensure effective air circulation and safety throughout the tunnel’s considerable length,” Moen noted.
An alert system for real-time incident detection will also be implemented to flag events such as vehicle breakdowns or heavy congestion, with cameras and radar providing vehicle monitoring.
While the closure of ferries will lead to job displacement in that sector, Moen stated that Rogfast will enhance local communities’ access to other employment opportunities, educational institutions, and public services. It is expected to benefit the local economy and the seafood industry positively by reducing logistics costs, enabling businesses to operate across a wider territory. “The project also creates substantial employment during construction and lays the groundwork for more sustainable and integrated regional development along Norway’s fractured western coastline,” she concluded.
This illustration depicts Rogfast’s dual-bore configuration, featuring a central emergency passageway. The design incorporates cross-passages, pedestrian evacuation routes, and safety systems for efficient traffic flow and emergency access.
This illustration depicts Rogfast’s dual-bore configuration, featuring a central emergency passageway. The design incorporates cross-passages, pedestrian evacuation routes, and safety systems for efficient traffic flow and emergency access. Skanska
Currently, the title for the world’s longest subsea stretch in a tunnel belongs to the Seikan Tunnel in northern Japan—a rail tunnel with a total length of 53.85 kilometers (33.5 miles), of which 23.3 kilometers (14.5 miles) are underwater.
The Channel Tunnel, which is also exclusively for rail connecting England and France, is shorter at 50.46 kilometers (31.35 miles), but its underwater section of 37.9 km (23.5 miles) surpasses that of Rogfast. However, Rogfast will sit substantially deeper below sea level than both Seikan or the Channel Tunnel, which reach seabed depths of 240 meters (790 feet) and 115 meters (377 feet), respectively.
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