The six lane, 6.5-kilometre (4.0 mi) twin tunnels will run from Cammeray to Rozelle, passing beneath Sydney Harbour.

It will then continue beneath Birchgrove and Balmain ending at the Rozelle Interchange, with connections to City West Link and WestConnex towards the M4 and M8 motorways.

[2] The Western Harbour Tunnel was introduced as a single project with the Beaches Link, aimed at reducing the level of traffic congestion in the greater Sydney area.

[8] In September 2021 the design and construction contract for the Warringah Freeway upgrade was awarded to a CPB Contractors and Downer Group joint venture.

[12] Early work activities commenced in March 2021, while major construction of the Warringah Freeway upgrade and the Western Harbour Tunnel began in late 2021 and 2022 respectively.