The units were constructed over 100 kilometres (62 mi) away in a casting basin at Port Kembla and then towed to Sydney Harbour.

The land tunnels were constructed by a combination of driving and cut-and-cover techniques, designed to be strong enough to withstand the impact of earthquakes.

Fresh air is drawn by an underground ventilation station on the north shore and is pumped to all sections of the tunnel through vented ducts.

They can expel it at up to 1,500 m3/s (53,000 cu ft/s) – equivalent to changing all the air in the tunnel every two minutes[7] with the capability of running in reverse in an emergency and all fans are rated for smoke extraction.

[9] $223 million of this was an interest-free loan from the NSW Government, to be repaid at the conclusion of the operating contract in August 2022 when the tunnel would be transferred to public ownership.

[10] The NSW Auditor-General had also raised concerns that the tunnel's expenses may make the operating company default on the $223 million loan,[11] however the government remained confident in it.

In 2006 the New South Wales government announced that all cash tolls on the Sydney Orbital Network would cease by 2010.

[14] This measure has substantially eased the traffic jams heading towards the electronic gantries, and providing increased convenience and time savings.

[16] It was eventually announced by the state government that the toll would continue, to be used for maintenance just like the Sydney Harbour Bridge.