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The Øresund Bridge: Connecting Sweden and Denmark

This megaproject may have the word bridge in its name, but it’s really much more than that. The Oresund Bridge, which connects Denmark and Sweden, is now one of those iconic structures known around the world that has begun to define the early 21st Century. Part bridge, part island and part tunnel, this is a true marvel of modern engineering. 

The Danish call it Øresundsbroen, the Swedish refer to it as Öresundsbron, but around the world, it’s often simply known as ‘The Bridge’. And if you happened to watch the wildly popular detective drama with the same name about a murder committed halfway across it, you’ll probably know all about it. 

The Oresund Bridge is the longest combined road and rail bridge in Europe and stretches nearly 16 km (10 miles), connecting the greater Copenhagen and Malmo areas. But as I said, this is much more than just a bridge. If you’re coming from Sweden, about halfway across the Oresund Sound, the stretch of water between the two countries, the bridge dives down onto an artificial island and disappears into a tunnel, only to reappear 4 km (2.5 miles) later next to Copenhagen airport. Why such an intricate combination of bridge, island and tunnel? Well, keep watching and find out. 

Plans Emerge  

Let’s just say from the offset, there are few pieces of engineering around the world quite as spectacular as the Oresund Bridge. It’s not the tallest, it’s not the longest and it’s probably not even the most visually striking, but travelling across it, you can’t help getting a sense that you are passing across the pinnacle of modern engineering. 

Building something like this would have been unimaginable 50 years ago but the idea of connecting Denmark and Sweden goes back to the second half of the 19th Century. The giant leap forward taken during the Industrial Revolution showed that in theory, a bridge connecting the two countries across the Oresund Sound was at least possible – though cost and obscure economic benefits were huge stumbling blocks. Instead, the two countries focused their efforts on the tried and tested, sea transportation, as it remained significantly easier and cheaper.

Charles XV photographed by Mathias Hansen
around 1865

In 1865, Swedish engineer Claes Adelsköld submitted a proposal to the King of Sweden, Karl XV, to build a railway tunnel beneath the Oresund Sound, but this was turned down. In 1889, an underwater railroad tunnel between Elsinore and Helsingborg was also rejected, both again due to exorbitant costs and a lack of real need for it. 

Things began to change at the dawn of the 20th Century. A new form of transportation arrived and would go on to revolutionise how we travel. The automobile gave people a level of freedom that had been unheard of until that point and suddenly the idea of a bridge across the Sound became a whole lot more enticing.    

During the 1930s there were serious discussions surrounding the project involving some of the leading nordic engineers at the time. But as we know, the 1930s started to go downhill fairly rapidly and both governments made the quite sensible decision that with all the build-up of arms throughout Europe, it probably wasn’t the best time to begin such a mammoth construction project. 

Discussions picked up again in the 1950s and rumbled on for the next few decades, but vehement opposition from farmers, environmentalists and eventually both governments, appeared to torpedo the proposal once and for all.  

But by the early 1990s, things had changed. The collapse of the USSR offered a glimpse of a tighter global connectivity and there was also the fact that both Denmark and Sweden were in the midst of serious financial crises. What better way to boost the economy and encourage trade, than building one of the world’s great engineering projects right on your doorstep. In 1991, both the Danish and Swedish governments issued a bilateral agreement on the building of the Oresund bridge and 126 years after the first proposal was submitted, the project had a green light.         

Designing 

But there was of course a long way still to go. Several factors meant that simply building a massive suspension bridge across the Oresund Sound was out of the question. Its proximity to Copenhagen airport meant that tall man-made objects were seen as far too risky. After all, the last thing you want after building such a superb structure is for a plane to smash into it in thick fog. But the bridge also couldn’t be too low as the Sound sees heavy boat traffic. The second issue was how to combine a road and rail connection. Your traditional cable suspension bridge often looks wonderful but is normally far too shaky for trains that rather annoyingly prefer a nice flat, vibration-free surface. Whatever design would be used, it would have to stretch the boundaries of modern engineering. 

A design contest was initiated, both as a way of garnering a wide selection of ideas, but also to gain plenty of publicity. The final design was composed of work drawn from Jorgen Nissen and Klaus Falbe Hansen from Ove Arup and Partners, and Niels Gimsing and Georg Rotne and it was ambitious, to say the least. 

The design called for a bridge measuring 8 kilometres (5 miles) that would travel from the Swedish coast to a small island roughly in the middle of the Sound. Oh, I should add that there weren’t actually any suitable islands in that particular stretch of water, so an artificial island would have to be created. On this newly formed island, the road and rail line would then disappear into a black hole and travel 4 kilometres (2.5 mi) through the Drogden Tunnel before reemerging on the Danish side of the Sound. 

The Bridge

The most visually impressive section of the Oresund Bridge must be the bridge itself – to be fair that’s probably because you can’t see the rest of it. As I mentioned earlier in the video, a traditional suspension bridge would have been unsuitable for train travel, so designers went with a cable-stayed design, which can transfer the massive weight through multiple cables back to the main towers.

Øresund Bridge from the air in September 2015
Øresund Bridge from the air in September 2015.By Nick-D is licensed under CC-BY-SA

The bridge consists of four main support towers, each 204 metres (669 ft) high – equivalent to a 60 storey building – and has 160 separate cables. Its towers are completely unconnected from one another, a design feature chosen so that in the worst-case scenario that a plane was to hit one of them, the bridge would in theory remain standing.  

A four-lane road passes along a horizontal girder that runs the length of the bridge, with two railway tracks running beneath the road. The height of the bridge leaves 57 metres (187 ft) of headroom for shipping to pass under the main span. 

The four support towers are connected to giant foundations that were first constructed on land. Each foundation measured 1,500 sq metres (16,145 sq ft), weighed 18,000 tonnes and reached 22 metres (72 ft) in height and were all lowered into trenches dug into the sound 17 meters (55.7 ft) deep. Once the foundations were in place, construction could begin to slowly raise each of the four support towers. When they reached 44 metres (144ft), the cross-beam was added and at 80 metres (262 ft) a steel box for the cables was also installed, with additional boxes added every 12 metres (39.3ft). 

The horizontal girders, where the road and railway lines run, were then added with each section measuring 140 metres (459ft) in length, 23 metres (75.4ft) wide and weighing 5.5 million tonnes each. Again, these were first constructed on land then installed during a painstakingly slow process where they were gradually winched up from a truly heavy weight lifting barge. In total, the bridge weighs some 82,000 tonnes, which is eight times that of the Eiffel Tower. 

Peberholm 

In August 1995, dredging work began in the Oresund Sound that would eventually create the artificial island of Peberholm. The island was formed almost entirely of dredged seafloor material, which is great if you simply want to build a landmass that can accommodate people and small structures, but made drilling a tunnel through it absolutely impossible – and I’ll go into a bit more detail on that in the next section. 

The first step was to build a perimeter that the island would eventually fill and to do this 1.8 million tonnes of large quarried stones were brought in from Sweden. This perimeter was carefully set using GPS and measured 12 km (7.4 miles) in length when completed. 

Then came the mammoth job of actually dredging enough seafloor material to create the island. This was done with some colossal pieces of machinery, most notably the largest dip dredger in the world, ‘The Chicago’, with a shovel capable of digging up 22 cubic metres (776 cubic ft) of seabed in a single scoop. This material was then transferred onto floating barges and moved to the island area where smaller diggers piled the seabed up to create the island.   

Peberholm is 4 km (2.5 mi) long with an average width of 500 metres (1,640 ft) and a height of 20 metres (66 ft) high. And this being built by the rather thoughtful Scandinavians, the entire island has been designated as a nature reserve. Seen very much as a natural experiment, the island has thrived since its creation and is now home to over 500 separate plant species. To add a little spice – or sting rather – in 2005, environmental researchers discovered the venomous Hobo spider on the island, a creature only found in certain spots in Denmark. It’s believed to have travelled there by train, which seems rather appropriate considering its name, Hobo. 

Drogden Tunnel

As I just mentioned, the fact that Peberholm was built entirely with seafloor material, meant that engineers needed to find another way of inserting 4 km (2.5 miles) worth of tunnel under the Oresund Sound. The word inserting might sound a little strange while talking about a tunnel, but essentially that’s exactly what happened. With tunnelling out of the question, the Drogden Tunnel was actually formed of multiple concrete tunnel segments built at a Danish factory that were then placed inside a tunnel trench that had been dredged from the Danish coast to the island of Peberholm in the middle of the Sound. 

This trench was 11 metres (36ft) deep, 46 metres (150ft) wide and had a total of 2 million cubic metres (70.6 million cubic ft) of seabed excavated from it. To kill two birds with one stone – or several billion stones if you want to be finicky – the material removed from the trench also made up part of Peberholm and was transferred there via purpose-built pipelines.  

The 20 segments were outrageously big, each measuring 175 metres (574ft) long, 38 metres (124ft) wide and 8.5 metres (27.8ft) high. They included five tunnel sections, two for cars, two rail transportation and one for emergency use. Each piece weighed a massive 55,000 tonnes – that’s four times the weight of the Brooklyn Bridge in case you’re interested – and also included 40,000 tonnes of reinforced steel bars which acted as the frame which was then filled with concrete. All 20 segments used a combined 7.5 trillion litres (1.9 trillion gallons) worth of concrete – which is enough to build a pavement around the earth – twice.    

The segments were all sealed shut which allowed them to be floated out into the sound – I know that sounds unbelievable but it really happened – before being lowered into the trench with the entire stretch then backfilled to create a tunnel that hadn’t actually been tunnelled – if that makes sense.  

And perhaps unsurprisingly considering the complexities, it was while building the tunnel that the project faced its most dramatic moments. An eagle-eyed worker on one of the barges suddenly noticed something metallic in a pile of rock that had been brought up from the seafloor. Taking a closer look, he was horrified by what he saw. The Chicago had dredged up an unexploded bomb from World War II and had then dumped it unknowingly on the barge. Miraculously, it hadn’t gone off and the site was quickly evacuated. The Danish Navy was called in to defuse the bomb and everybody breathed a sigh of relief. 

But things weren’t over. Another bomb was soon discovered and the decision was taken that no area could be dredged until it had been swept for bombs first. Astonishingly, a total of 16 Allied bombs from the Second World War were discovered during the construction of the Oresund Bridge, but all were diffused safely.            

Opening

The Øresund Bridge took nine years to build and despite finding far too many unexploded bombs for comfort was finished three months ahead of schedule. It officially opened to the public during several ‘open days’ between 9th and 12 June 2000 and was inaugurated with plenty of gusto on 1st July 2000. 

It cost a total of DKK 30.1 billion – around $4.5 billion at the time, which equates to roughly $6.9 billion today. Broadly speaking, the Øresund Bridge has been a great success and in its busiest year, in 2017, on average just over 20,000 cars passed over the bridge each day and roughly 14,000 rail commuters passed across the Oresund Sound. Since its opening, nearly 250 million people have crossed the Oresund Bridge, either by car or by rail. It is however not cheap to drive on, with toll costs for a single trip currently around the $50 mark – though there are considerable discounts for frequent users. With this kind of pricing, it’s not surprising that Bridge will have effectively paid for itself by 2030.      

This is a wonderful bit of engineering which broke countless records for size and distance. It was a project that faced serious hurdles because of its location but one which engineers and designers were able to safely navigate around. As I said right at the start of the video, this is one megaproject that really gives you a sense of grand achievement and where humans have pushed the boundaries of what’s possible. And as we’ve seen, this is a bridge that’s so much more than just a bridge.   

Credits

“Öresundsbron” by Håkan Dahlström is licensed under CC-BY

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