Bridging the Gap: The Engineering Triumph of Finland’s Hailuoto Link

For decades, getting to and from Hailuoto—the largest island in the Gulf of Bothnia and home to about 1,000 residents near Oulu, Finland—meant relying entirely on road ferries. While the 25-minute ferry ride offered a scenic introduction to the island’s unique nature, it was also prone to weather delays, seasonal ice challenges, and growing maintenance costs.

That routine changed forever when the Hailuoto causeway and bridge project officially opened to traffic. Replacing a maritime crossing that had defined the region for generations, this massive infrastructure undertaking has permanently transformed travel to the island.

A Massive Infrastructure Feat

The road link project is one of the most significant transport infrastructure developments in Finland in recent years. Spanning a total length of 8.4 kilometers, the connection features 7.7 kilometers built directly across the sea. Rather than a single continuous bridge, the project is a hybrid engineering marvel combining rock embankments with two major bridges:

• Huikun silta (Bridge S1): A 767-meter-long continuous steel-concrete composite girder bridge featuring nine spans and an 18-meter vertical clearance.
• Riutun silta (Bridge S2): A 737-meter-long continuous prestressed concrete girder bridge with ten spans and a 5-meter vertical clearance.

Constructed by the HAIKI alliance and key partners like GRK, the physical building phase kicked off in May 2024 and reached its final completion milestones.

Overcoming Complex Geotechnical Hurdles

Building a multi-kilometer causeway and two massive bridges across open sea water is never simple, but the Hailuoto project faced an especially tricky geological challenge: the Muhos formation.

Roughly 1.3 billion years ago, the bedrock in the area subsided by about a kilometer, filling up with thick layers of claystone and soft sediment reaching tens of meters deep. Furthermore, the seabed’s chemical environment featured unusually high levels of chlorides, sulfates, and electrical conductivity.

To anchor the bridges securely into stable sand layers beneath the soft sediment, engineers drove massive steel pipes—some up to 1,200 millimeters in diameter—deep into the seabed. Because of the aggressive chemical conditions, these heavy steel piles were designed to act alongside reinforced concrete structures to ensure a target design service life of a full century.

Life After the Ferries

The most immediate impact of the new causeway is speed and convenience. What used to be a rigid schedule dictated by ferry timetables has been replaced by a smooth, 80 km/h roadway where drivers can make the crossing in roughly eight minutes. Local public transit lines, like Oulu’s regional bus routes, adapted immediately, cutting travel times down significantly for commuters and visitors alike.

While the traditional ferry ports have retired, the project was meticulously designed to blend into the sensitive coastal landscape. Intentionally built without highway lighting to protect local dark-sky and natural aesthetics, the causeway respects the fragile ecosystem of the region while giving Hailuoto a reliable, modern lifeline to the Finnish mainland.