Brusio spiral viaduct

Brusio spiral viaduct is a famous feature of the World Heritage Rhaetian Railway . It was needed "to limit the railway's grade to the required maximum of 7%, so the train would not slip on the way up, or be uncontrollable on the way down. Geological factors prevented the boring of the spiral tunnel that had originally been planned. Engineers therefore decided to construct on the valley floor a 360 degree curve with a 50 to 70 m (160 to 230 ft) radius, and the viaduct forms part of that curve"(Wiki).

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