The Rozelle interchange, a twisting maze of overlapping tunnels some 40 metres below Sydney’s inner west, could be the most complex underground junction ever built, according to its project director.

A draft design of the last and most complicated stage of WestConnex was released to the Herald on Thursday (and is published in full at the bottom of this article), revealing how the new M4 and M5 tunnels, the ANZAC Bridge and Iron Cove will be linked together.

Rozelle Interchange project director Tarnjit Chahal. Credit:Steven Siewert

The three-storey underground interchange, which varies in depth between 35 and 65 metres, will act as a linchpin for the 33-kilometre, $16.8 billion WestConnex project, and also provide the connection to a future Western Harbour Tunnel.

Project Director Tarnjit Chahal, who has worked on tunnelling projects around the world, said he wasn’t aware of a more complex piece of underground road infrastructure.