Broadly speaking, there are two ways to build a bridge. The first is to build extensive, sturdy scaffolding to hold the elements in place as work crews assemble them. The second is to start with a pier, and build outwards in both directions at the same pace, ensuring balance. Both methods are time-consuming and expensive.

That's why Johann Kollegger, a professor at the Institute of Structural Engineering at Vienna University of Technology (TU Wien), has been working on an alternate solution since 2006. After years of testing and research, he and his team recently unveiled it. Or unfolded it, I should say.

Kollegger's fantastical method consists of two girders placed vertically within a crane-like skeleton. This is hoisted into place by a crane and set like a post. Then the two girders are unfolded, slowly and steadily, in opposite directions:

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Those girders span Austria's river Lafnitz, and are part of the Fürstenfeld Motorway.

The girders themselves consist of thin-walled prefabricated elements with steel reinforcement and are initially hollow. Once they have reached the final horizontal position they are filled with concrete. "Erecting bridges using scaffolding usually takes months. The elements for the balanced lowering method on the other hand, can be set up in two to three days, and the lowering process takes around three hours," says Johann Kollegger.

The new bridge construction method not only saves time but also money, and the durability of the bridge is the same if not better than that of bridges built using other methods, as Kollegger emphasizes. The balanced lowering method (or lifting method when building bridges with high piers) is particularly advantageous for the erection of bridges in difficult terrain or terrain that should not be disturbed – for example a nature reserve, as was the case for the Lafnitz Bridge that is now being erected.

"Now that we have proven that the method is well-engineered and works perfectly," says Kollegger, "we hope that it will prevail and will soon become one of the common bridge building methods that are used around the globe and that the S7 Motorway will become an international pioneer."