Higher Road

The Millau Viaduct bridge, is a cable-stayed road bridge which spans over the River Tarn in the Massif Central mountains near Millau in southern France.

Designed by the French structural engineer Michael Virlogeux and British architect Norman Foster, it is the tallest bridge in the world with one mast's summit being taller than the Eiffile tower at 343m (1,125ft) above the base of the structure.

Deck

The metallic deck, which appears very light despite its total mass of around 36,000 tonnes, is 2,460m (8,070ft) long and 32m (105ft) wide. It comprises eight spans. The six central spans measure 342m (1,122ft), and the outer spans are 204 meters (669ft) Theses are composed of 173 central box beams, the spinal column of the construction, onto which the lateral floors and the lateral box beams were welded. The central box beams have a 4m (13ft) cross-section and a length of 15-22m (49-72ft) for a total weight of 90 metric tons.

The deck has an inverse Airfoil shape, providing negative lift in strong wind conditions. 

Masts 

The seven masts, each 87m (285ft) high are weighing around 700 tonnes, are set on top of the pylons. Between each of them, eleven stays (metal cables) are anchored, providing support for the road deck.

Construction of one of the mast's.

Stays

Each mast of the viaduct is equipped with a monoaxial layer of eleven pairs of stays laid face to face. Depending on their length, the stays were made of 55 to 91 high tensile steel cables, or strands, themselves formed of seven strands of steel (a central strand with six intertwined strands). Each strand has triple protection against corrosion (galvanisation, a coating of petroleum wax and an extruded polyethylene sheath). The exterior envelope of the stays is itself coated along its entire length with a double helical weatherstrip. The idea is to avoid running water which, in high winds, could cause vibration in the stays and compromise the stability of the viaduct.

Mast with multiple stays consisting of 55-91 high tensile steel cables. 

Surface

To allow for deformations of the metal deck under traffic, a special surface of modified bitumen was installed by research teams from Appia. The surface is somewhat flexible to adapt to deformations in the steel deck without cracking, but it must nevertheless have sufficient strength to withstand motorway conditions (fatigue, density, texture, adherence, anti-rutting etc.) The "ideal formula" was found only after two years of research.

Asphalt compation

 
The viaduct is part of the autoroute axis from Paris to Montpellier, and construction cost was approximately 400 million Euros (540 million CAD)

It was built to reduce traffic on the route from Paris to Spain along the stretch passing through the valley near the town of Millau, especially during the summer when roads became jammed with holiday traffic.

The Millau bridge.What an incredible sight to see both on and off of the levitated motorway.

Of course it had to have been featured in an episode of Top Gear on BBC. 

Skip to 4:32

Good stuff.