In July 1965, a 12km tunnel dug deep beneath the Alps was opened to traffic, making it the longest vehicular tunnel in the world. Linking France and Italy, the Mont Blanc Tunnel was a remarkable feat of engineering.

Franco Cuaz, a consultant on the project and the tunnel's first operations manager, spoke to Mike Lanchin in 2017 about the risks and challenges of the ambitious project.

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(Photo: The Mont Blanc Tunnel. Credit: AFP via Getty Images)