MACAO: Stepping onto a shuttle departing from Hong Kong, passengers are struck by the scale of the bridge, as it carries them toward Macao. Behind them, the land quickly fades, and for the next half hour, only open sea stretches on either side of the bus. The 55 km-long passage is the world’s longest bridge-tunnel sea-crossing, spanning the waters of the Lingding Channel in the Pearl River Estuary, a key waterway in southern China that flows into the South China Sea. It connects China’s two special administrative regions — Macao and Hong Kong — and the mainland city of Zhuhai.