Crossing the Øresund Strait between Copenhagen and Malmö means moving through three different kinds of infrastructure. A road and railway first pass beneath the water in a tunnel, emerge onto a small artificial island, and then continue across a long bridge toward Sweden. The sequence is not a flourish. It is an engineering answer to a crowded stretch of sea where ships need a clear passage and aircraft need safe approaches to Copenhagen Airport.
The Øresund fixed link opened in 2000. Its roughly 16-kilometre route combines the Drogden Tunnel, the island of Peberholm and the Øresund Bridge. Together, the parts carry both motorway traffic and trains. Designing them as one connected system meant solving different problems along a single crossing rather than insisting on one structure from shore to shore.
Why the crossing changes from tunnel to bridge
A bridge is often the more visible choice for a long water crossing, but a tall structure near an airport can conflict with flight paths. On the Danish side, the route runs close to Copenhagen Airport. The crossing therefore begins underwater in the Drogden Tunnel, avoiding a high bridge in that area. Farther along, where a bridge can rise without the same constraint, the route comes above the surface.
The tunnel also leaves a navigable passage across the strait without bridge supports standing in the water along that section. The overall design has to accommodate shipping as well as vehicles, trains and aviation. Instead of treating those requirements as separate projects, engineers joined tunnel, island and bridge into a continuous transport link.
That arrangement brings its own challenge: the road and railway must transition smoothly between structures built in different ways. The tunnel reaches Peberholm, a human-made island in the middle of the strait. From there, the route continues over the bridge to Sweden. The island serves as the physical and engineering transition point between the submerged and elevated sections.
Building a tunnel on the seabed
The Drogden Tunnel is an immersed-tube tunnel. Rather than excavating a conventional tunnel deep beneath the strait, builders placed large prefabricated concrete sections in a prepared trench on the seabed. The sections were transported into position, lowered, joined and covered. The finished tunnel is about four kilometres long, with most of that distance made up of the immersed section.
Each tunnel element had to be heavy and strong enough for its permanent job, yet manageable during construction. The tunnel carries two railway tracks and a motorway in each direction, with a separate service passage. Keeping these routes enclosed in one connected structure saves the need for distinct crossings for cars and trains, but it also makes the tunnel’s layout and safety systems essential parts of the design.
Immersed-tube construction depends on precise connections. If sections do not meet and seal correctly, water can enter the joints. The work also requires careful control of the seabed trench and the elements’ position as they are lowered. Once in place, the sections are protected by a covering layer. The result is a road-and-rail passage beneath the strait rather than a bridge that would need to rise above it.
Peberholm: more than a midpoint
Peberholm is an artificial island about four kilometres long. It gives the tunnel a place to emerge and provides the approach to the bridge. That may sound like a simple handoff, but the island makes a complex combination of structures function as a continuous route. It also separates the Danish tunnel section from the bridge’s long approach across the water.
The island was built using material dredged during work on the crossing. Its position and shape were part of the project’s larger design: the route needed a transition area while keeping the main shipping channel open. Peberholm is not the same as the nearby natural island of Saltholm; the fixed link was designed around the strait’s existing geography rather than simply extending a causeway across the water.
A bridge carrying two transport systems
On the Swedish side, the link rises onto the Øresund Bridge. The bridge section is nearly eight kilometres long and includes a high-level cable-stayed span, whose central span measures about 490 metres. The main pylons rise roughly 204 metres above the water. The elevated roadway and railway provide clearance for ships to pass underneath.
Road and rail share the bridge structure but run on separate levels: the railway is below the motorway. That arrangement makes the crossing compact compared with building entirely separate road and rail bridges, while requiring the structure to carry the weight and movement of both. The railway also connects to the broader networks on each side, allowing the link to serve regional trains as well as road vehicles.
The bridge is not simply a scenic finale after the tunnel. Its height, span and approach viaducts are part of the same balancing act as the underwater section: provide a reliable transport route and preserve room for other uses of the strait. The combined link demonstrates how a major crossing can be designed around changing conditions along its route.
One crossing, several engineering answers
The Øresund link is often described as a bridge, but that shorthand leaves out much of the design. Its tunnel addresses the airport-side constraint; its bridge provides a high passage over the water; and Peberholm joins the two. Across the whole route, road and rail share a fixed connection while ships continue to use the strait.
That does not make the crossing a universal blueprint. Local geography, air traffic, navigation and environmental conditions determine what is practical for any particular project. The enduring lesson is more specific: infrastructure can change form to meet different constraints in different places. In the Øresund, the most useful solution was not one enormous bridge or one long tunnel, but a carefully connected sequence of both.
