Égratz Viaduct, Concrete viaduct in Passy, France
The Égratz Viaduct is a concrete bridge that crosses the Arve Valley near Passy, stretching for around 1,470 meters while reaching a height of 68 meters above the ground. It uses a curved box girder design that is about 11 meters wide, with individual spans measuring approximately 49 meters across.
Built between 1977 and 1981 and opened to traffic in 1982, the viaduct doubled the old mountain-flank road known as the descente des Égratz. It was meant to ease traffic between the A40 autoroute and the Mont-Blanc tunnel, opened in 1965. The climbing carriageway uses the viaduct while the old road, now one-way, carries descending traffic.
The N205 crosses the Arve three times along the viaduct's curve, and for about five kilometres between l'Abbaye and le Châtelard the two carriageways are swapped, so drivers have oncoming traffic on their right. The descent stays on the old mountain road, single-direction, while the viaduct carries the uphill express lanes. The viaduct appeared in aerial photography in the 2016 film Our Kind of Traitor.
The structure serves as a main passage connecting both sides of the valley through the Route Nationale N205, allowing vehicles to cross continuously throughout the day. A major renovation took place in 2015 to maintain its safety and ensure reliable use for the ongoing traffic that depends on this crossing.
The box girders were built using prestressed concrete, a technique that puts the concrete under pressure to give it extra strength for longer spans. This method was an advanced solution for the 1980s and allowed the bridge to cover such large distances across the valley.
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