When it opened on 17 December 2004, Millau Viaduct set new standards in both planning design and construction, as well as the record as one of the largest cable-stayed bridges in Europe.

At 2.4km long and 270m above the river at its highest point, the Millau viaduct spans a 2km valley in the Massif Central mountain range and forms the final link in the A75 highway from Paris to Barcelona.

The road has two lanes in each direction and costs €400m, which will be recouped by the builder, Eiffage, under a 75-year concession.

The Millau Viaduct rest area, which can be accessed from the A75 motorway or from Millau via the D911 and the Boulevard du Viaduct roads, was inaugurated in July 2017. The viaduct reached a threshold of five million vehicles for the first time on 29 December 2017.

Bridge design

Two major challenges were identified in building the structure, namely crossing the River Tarn and spanning the huge gap from one plateau to the other. The solution proposed is unique using seven pylons instead of the typical two or three. It is several metres taller than the other famous French landmark, the Eiffel Tower.

Famous British architect Norman Foster was in charge of the viaduct’s appearance. It has been designed to look as delicate and transparent as possible. Each of its sections spans 342m and its columns range from 75m to 235m in height over the river Tarn. It uses the minimum amount of material, which made it less costly to construct, namely the deck, the masts rising above the road deck and the multi-span cables are all in steel.

Seven piers

The seven piers of the Millau Viaduct are sunk in shafts of reinforced concrete in a pyramidal shape and divided in an overturned V. The shrouds are anchored and distributed in semi harps. The programme utilised hundreds of high-pressure hydraulic cylinders and pumps to push-launch the deck spans in place and a PC-synchronised lifting system to lift the auxiliary piers. Enerpac was awarded the major contract to supply the hydraulic system for lifting and pushing the bridge spans and piers for the bridge.

Interestingly, the Millau Viaduct is not straight. A straight road could induce a sensation of floating for drivers, which a slight curve remedies. The curve is 20km in range. Moreover, the road has a slight incline of 3% to improve visibility and reassure the driver.

Bridge construction

Construction began in October 2001 and, by November the following year, the highest pier had already reached 100m in height. Launching the deck started in February 2003 and was completed by May 2004.

The deck is unusually constructed from new high-grade steel as opposed to concrete. This helped the deck to be pre-constructed in 2,000 pieces at Eiffage’s Alsace factory and GPS-aligned by 60cm at a time.

The Millau Viaduct is supported by multi-span cables placed in the middle. To accommodate the expansion and contraction of the concrete deck, there is a 1m empty space at its extremities and each column is split into two thinner and more flexible columns below the roadway, forming an A-frame above the deck level.

Construction work used approximately 127,000m³ of concrete, 19,000t of steel-reinforced concrete and 5,000t of pre-constraint steel, namely cables and shrouds. The project needed 205,000t of concrete, of which 50,000m³ is reinforced. In total, the viaduct weighs 290,000t.

A 3m-wide emergency lane provides increased security. In particular, it prevents drivers from seeing the valley from the viaduct.

As the bridge will be exposed to winds of up to 151km/h, side screens are used to reduce the effects of the wind by 50%. Therefore, the speed of the wind at the level of the road reflects the speed of the wind found at ground level around Larzac and Sauveterre.

An extension work, which began in 2005, included the installation of 30km/h electronic toll collection lanes and payment lanes with recycling.

Toll station

An 18-lane toll station 6km north of the Millau Viaduct is housed under a structure made of a special concrete patented by the group Eiffage. The toll plaza includes a CCTV connection to the viaduct and the highway. It also accommodates technical and administrative services.