Despite being quite a common fixture around the world, the construction of tunnels is often an incredible story of advanced technology and effective conveyor belt installation that works to bore through the earth itself.
From the Gotthard Base tunnel, the longest railway tunnel in the world, to the labyrinthine and exceptionally well-used tunnels of the Shanghai Metro, every tunnel tells a story of the incredible people and machines that made them and the journeys of millions of people that made it essential.
However, one of the most staggering engineering marvels is the Øresund Bridge that connects Sweden and Denmark, which not only is the longest combined road and rail bridge in Europe but also isn’t entirely a bridge.
What is most striking about the route is not the five-mile bridge that starts at Malmo but instead the artificial island of Peberholm and the 2.5-mile Drogden tunnel that connects it to Copenhagen in Denmark.
There is a rather unique sensation of travelling along a huge bridge across a vast strait before diving underground as part of the journey and it came about for rather peculiar reasons.
When the bridge was finally agreed to by Denmark and Sweden in 1991 after nearly a century of attempts to create a bridge across the Øresund strait, there was a dilemma in running a bridge the entire way.
Copenhagen Airport is exceptionally close to where the exit of the bridge was planned to be, and that could potentially cause major issues with air traffic whilst the bridge is being constructed.
As well as this, the struts of the bridge risk creating ice floes that would affect Copenhagen’s harbour and potentially block channels for ships, as well as requiring the bridge to be built higher, creating a steeper gradient which could cause issues for freight trains.
Instead, they opted for the expensive route of building an artificial island and nature reserve, as well as the construction of an underwater tunnel.
The tunnel part is made from 20 prefabricated segments made of reinforced concrete laid in the correct position before being sunk using a method known as immersed tube construction.
After this, a stone ballast is laid on top to keep the tunnel at the bottom of the strait and unaffected by water flow.
It consists of five tunnels. Two of these are two-lane roads going in each direction, two are train tunnels and there is a fifth, which carries a service tube, escape tube and tube for carrying data cables from one country to the other. All of these tubes have been laid side by side.
Construction of the bridge ultimately started in 1995 and despite one of the tunnel segments being skewed and 16 unexploded bombs being found on the seafloor, the tunnel was completed in August 1999, three months ahead of schedule and almost a year before its grand opening on 1st July 2000.
Initially, the bridge saw increased traffic but not as much as many were expecting, but by 2005 traffic levels increased considerably due to Danish commuters choosing to buy property in Malmo, the third-largest city in Sweden, rather than in the capital of Denmark.
