This vast sea bridge will soon connect three of the world's most densely populated cities - by spanning the width of China's Pearl River Delta. At its longest stretch, the Hong Kong-Zhuhai-Macao Bridge measures 29.6 kilometres and includes a 6.7-kilometre stretch of tunnel between two artificial islands.

"This bridge is one of the most technically challenging projects in the history of transportation in China," claims Su Quanke, chief engineer of the HZMB Authority, the company overseeing the ambitious project.


The structure's 40-metre-deep submerged tunnel creates a gap in the bridge, which will allow cargo ships to pass through and up into the Pearl River Delta, home to some of China's biggest industrial cities. But to get from the bridge to the underwater tunnel and back out again at the other side, cars will have to drive through two man-made islands situated at each end of the tunnel. To build the 100,000-square-metre islands, engineers drove huge steel cylinders into the riverbed before filling them - and the area they enclosed - with sand. Without the tunnel, Su explains, the bridge would have been so tall its pylons would exceed the height limits for structures near Hong Kong International Airport.

The bridge is built to withstand the strong winds and typhoons that batter the Pearl River Delta every summer. When structural engineers were drawing up plans for the project, they ran wind-tunnel simulations to make sure it could hold out against tropical storms, which can carry gusts well in excess of 100kph.

When it comes to infrastructure projects of this scale, "Size is not the only challenging aspect," Su says. Difficulties co-ordinating between regional governments and concerns over the construction's impact on the habitat of Chinese white dolphins have pushed the completion date back to late 2017. Until then, there's always the ferry.