The Barnett Government will today release one of its biggest and most expensive pre-election commitments — a $520 million rail link between Thornlie and Cockburn.

Planning and negotiations for the 17.5km link will begin this year, with completion due in late 2023.

First seriously proposed 17 years ago, the line will connect the Armadale and Mandurah lines.

It will follow an existing freight track alignment and include new stations at Nicholson and Ranford roads.

Transport Minister Bill Marmion said the new link would result in faster journeys for commuters who would otherwise need to travel into the CBD and transfer to another service.

“It’s the missing link in Perth’s southern transport network and will revitalise the areas through which it runs,” he said.

The connection will improve travel to and from the new Perth Stadium, with fans able to travel along the link to Cockburn, soon to be the home of the Fremantle Dockers, and, potentially, all the way to Mandurah.

Planning and negotiating with freight line owners Brookfield Rail is expected to take two years and shifting the freight line will take another two.

Construction of the passenger rail line is expected to begin in 2021, with the stations to be built in 2022.

The stations are expected to have more than 3000 boardings each day. They will include bus interchanges, park-and-ride facilities for 1400 cars and bike storage.

Camera Icon The new line. Illustration: Supplied Credit: Supplied

“Land around the two new stations will become vibrant urban precincts, with a mix of housing, apartments, retail outlets and other businesses,” Mr Marmion said. “Thousands of jobs will come with that.”

The State Government believes 500 jobs will be created during the construction of the link.

In its long-term transport plan released for public comment in July, the State Government nominated the extension of the Thornlie line to Cockburn as a necessary project “to cater for growing suburbs”.

The plan said the line was needed before Perth’s population reached 2.7 million, in about 2030. It also indicated that by the time Perth’s population hit 3.5 million in about 2050, a northern extension of the Thornlie line would be needed to join the Forrestfield airport line, which is currently under construction.

In mid-2015, the RAC described the Thornlie to Cockburn link as a priority project that would “offer a viable and highly attractive public transport option to commuters currently competing with freight and commercial transport along Roe Highway”.