It is on track to open to the public within 12 months, but underneath Yarraville, vehicles can now travel the full length of the tunnels that are to provide a long-awaited alternative to the West Gate Bridge.

Premier Jacinta Allan played bus driver on Monday to celebrate a key milestone for the West Gate Tunnel project, driving the entire four-kilometre length of the outbound tunnel for the first time, albeit two years after the project was originally scheduled to open in 2022.

Taking up the benefits, Allan promised the project would open before the end of 2025 and “transform transport around the city”.

“The delivery of the West Gate Tunnel project is going to save travel time, which means people will get home safer, sooner, with more time to do the things that they want to do, not be stuck in traffic,” she said.

Once complete, the two tunnels will take traffic underground from between the West Gate Freeway and the Maribyrnong River, where vehicles will connect to a new traffic bridge above Footscray Road.

The state government estimates the $10 billion project, once opened, will remove 9000 trucks a day from local streets in the inner-west, slash travel time for commuters by 20 minutes and provide another option when traffic is congested on the West Gate Bridge.

“Just about everyone has had an experience where there is an incident on the West Gate Bridge and not only does it grind traffic to a standstill ... it has a knock-on effect across the city,” Allan said.

Inside the sparse, three-lane cavities, work is under way to install more than 10,000 architectural panels on the tunnel walls, with more than half already in place.