Deep ventilation works mark progress on world-record subsea road tunnel

A second ventilation shaft has broken through on the E02 Kvitsøy section of Norway’s Rogfast Tunnel, marking another important underground milestone on what is planned to become the world’s longest and deepest underwater road tunnel.

The Rogfast Tunnel will run for almost 27 km beneath Boknafjord in western Norway, creating a fixed road connection between Stavanger and Haugesund and giving the island municipality of Kvitsøy a permanent link to the mainland. Today, these journeys depend on ferry crossings. Once complete, the tunnel is expected to make travel and freight movement more predictable by removing dependence on ferry schedules, weather windows and queues.

The newly completed shaft is one of two major ventilation shafts on the Kvitsøy package. The first shaft broke through in March 2026, and the second has now followed. Each shaft is approximately 230 m deep, with diameters of about 8.6 m and 9.4 m. They will ventilate the tunnel during construction and remain part of the completed road tunnel’s permanent ventilation system.

Ventilation shafts are sometimes treated as secondary elements beside the main tunnel drive, but Rogfast shows why that is misleading. In a long, deep subsea road tunnel, air management is fundamental to safety, construction productivity and long-term operation.

During construction, ventilation supports blasting, mucking, plant operation and worker safety deep below the fjord. During operation, the system must manage vehicle emissions, smoke control, pressure effects and emergency scenarios. At Rogfast’s scale, a shaft is not just an opening to the surface. It is part of a wider life safety system that must work with technical buildings, emergency stations, cross-passages, pumping systems and tunnel control infrastructure.

The E02 Kvitsøy package is described as the most complex part of the project. It includes about 8.8 km of 10.5 m diameter double-tube, two-lane tunnel, an underground intersection and a ramp connection to Kvitsøy. The package also includes 17 technical buildings, 154 emergency stations, 38 cross-passages and five pumping stations.

Rogfast is being excavated through rock beneath the sea, where geological uncertainty, high water pressure and weak zones can strongly influence progress. Norway’s use of drill and blast tunnelling is well established, but the method still depends on continuous adaptation to actual rock conditions.

For a tunnel of this length and depth, the visible breakthrough is only one part of the engineering story. The permanent success of the project will depend on ventilation, drainage, waterproofing, rock support, fire safety, emergency access and maintenance systems working as one integrated underground network.

The second Kvitsøy shaft breakthrough therefore represents more than progress on a vertical excavation. It shows that the hidden infrastructure needed to make Rogfast safe, buildable and operable is taking shape beneath Boknafjord.