Construction work is currently in progress to expand the Metro system under Sydney Harbour and the Central Business District (CBD) to include 41miles (66km) of twin tracks and 31 stations by 2024.

The 3.45km twin tunnel underground rail link will run up to 42m below the city centre and includes the construction of two new inner-city underground stations (Karangahape and Aotea) and rebuilding the existing Mt. Eden Station.

The Metro Tunnel provided some unique challenges for the ventilation design, including space and noise constraints plus the location on excavation works within the CBD.