The first major stage of Sydney's WestConnex project will open to traffic more than three years after construction started on the $3.8 billion underground section.
The new M4 tunnels between Homebush and Haberfield are expected to slash up to 20 minutes off a trip from Parramatta to the Sydney CBD.
The 5.5km twin tunnels run three lanes in each direction, bypassing 22 sets of traffic lights.
The eastbound tunnel is expected to open from 2am on Saturday, followed by the westbound tunnel about an hour later.
There will be no toll-free period with motorists charged up to $7.89 per trip, depending where they enter the M4.
NSW Premier Gladys Berejiklian said drivers could use free alternative routes if they wished to bypass tolls.
She said the project would help commuters spend less time in traffic.
NSW Roads Minister Andrew Constance expected the new tunnels to reduce the traffic on Parramatta Road by more than 50 per cent.
Deputy Prime Minister Michael McCormack cut the ribbon for the long-awaited project with Ms Berejiklian and Mr Constance on Friday.
The federal government has contributed $1.5 billion to the total $16.8 billion WestConnex build, a project he said would get people home "sooner and safer".
The next stage of the WestConnex project - an extension of the M5 to St Peters - is expected to open in 2020.
The final stage will link the new M4 at Haberfield to the new M5 at St Peters.
© AAP 2019