The 5.5km long M4 tunnels will allow drivers from Western Sydney to bypass a significant section of stop-start traffic on Parramatta Road and connect directly onto the City West Link.
The M4 tunnels are part of WestConnex that will link Sydney's west and southwest with the city, airport and port precinct in more than 30 kilometres of continuous motorway.
Once completed, WestConnex will provide a bypass of up to 52 sets of traffic lights.
Premier Gladys Berejiklian said within two years, around 67,000 trips are expected in the M4 tunnels every day.
"Once all of WestConnex is complete in 2023, drivers will be able to get from Penrith to the Anzac Bridge without having to stop at a single traffic light and travel times from Parramatta to Sydney Airport will fall by up to 40 minutes," Ms Berejiklian said.
"Traffic volumes on sections of Parramatta Road will also be reduced by more than 50 per cent."
