Hailuoto Bridge: Finland’s New Island Connection

Bridging the Gap: The Engineering Marvel of the Hailuoto Fixed Connection

For decades, getting to Hailuoto—the largest island in the Gulf of Bothnia and one of Finland’s most unique cultural landscapes—meant timing your life around a ferry. For about 1,000 permanent residents and countless tourists who flock to the island’s sandy beaches and nature trails, the 25-minute, 6.8-kilometer ferry ride from the mainland was a routine part of travel.

However, relying entirely on aging road ferries came with steep operating costs and weather-related vulnerabilities. Enter one of Finland’s most significant modern infrastructure achievements: the Hailuoto fixed road and bridge connection, which officially opened to traffic, transforming a journey that used to take nearly half an hour into a swift, eight-minute drive.

Anatomy of the Project: More Than Just Bridges

While colloquially referred to as the “Hailuoto Bridge,” the project is actually an ambitious 8.4-kilometer roadway combination consisting mostly of a sea causeway, complemented by two major bridges named Huikun silta and Riutun silta.

• The Route Breakdown: Out of the 8.4 kilometers of new roadway, an astonishing 7.7 kilometers run directly across the sea. The core of the causeway was built using an immense embankment of blasted and crushed rock.
• Huikun Silta (Bridge S1): A continuous steel-concrete composite girder bridge spanning 767 meters across nine spans, featuring a clearance height of 18 meters to allow marine traffic underneath.
• Riutun Silta (Bridge S2): A continuous prestressed concrete girder bridge spanning 737 meters across ten spans, with a 5-meter clearance.

Conquering Extreme Engineering Challenges

Building a multi-kilometer transport link across a northern marine environment is no small feat. The project team faced fierce geotechnical hurdles right from the start.

The seabed sits in what is known as the Muhos formation—an ancient geological depression filled with soft sediment and claystone layers descending tens of meters deep. Furthermore, the marine chemistry of the area presented unusually high chloride and sulphate contents, pushing structural durability requirements to the absolute limit.