Faced with winds up to nearly 125 mph (200 km/h) in the Tarn valley, the Millau Viaduct required thorough studies. 36,000 tons of steel were needed to build its deck supported by 1,500 tons of cables. Eleven pairs of fan-shaped metal guy wires support the deck in each of the seven pylons. On each pillar, sensors monitor the slightest movement or deformation. A special plexiglass windbreak screen protects motorists from gusts of wind on either side of the deck.