The new M4 tunnels between Homebush and Haberfield will open on Saturday, with the NSW government saying it will slash travel times for thousands of drivers.
The first underground sections of Sydney's mammoth WestConnex project will be open to traffic from Saturday.
The new M4 tunnels between Homebush and Haberfield are expected to shave up to 20 minutes off a trip from Parramatta to Sydney's CBD.
"This is yet another major project which will allow people to spend less time in traffic and more time doing what they want," NSW Premier Gladys Berejiklian said in a statement on Wednesday.
The $3.8 billion, 5.5-kilometre twin tunnels are three lanes in each direction - extending the widened M4 to Haberfield and bypassing 22 sets of traffic lights.
The government predicts it will cut overall traffic on Parramatta Road by 53 per cent by 2021.
"WestConnex will take up to 10,000 trucks a day off Parramatta Road, which is welcome news for anyone who sits in bumper-to-bumper traffic on that notoriously congested corridor," NSW Roads Minister Andrew Constance said.
Motoring group NRMA wants the new section to be toll-free for at least the first month.