A 3-kilometre tunnel to Fremantle will be built as part of the next stage of the $1.9 billion Perth Freight Link if the Barnett Government is re-elected in March.

Key points: Construction of Roe 9 and tunnel due to start in 2020 if Barnett Government re-elected

Construction of Roe 9 and tunnel due to start in 2020 if Barnett Government re-elected No current plans to take Perth Freight Link into North Fremantle and Fremantle Port

No current plans to take Perth Freight Link into North Fremantle and Fremantle Port Greens, Labor condemn decision as policy on the run, say it won't fix transport problems

Premier Colin Barnett announced plans for the tunnel to run underneath homes in White Gum Valley, Beaconsfield and Hilton in the $903 million stage two of the freight link, originally designed to provide a seamless route from Perth's industrial eastern suburbs to Fremantle Port.

Stage one of the project — the controversial extension of Roe Highway west of the Kwinana Freeway known as Roe 8 — is set to take the freight link to Stock Road.

The tunnel would then be built from the Stock–Winterfold Road intersection in Hilton to High Street in East Fremantle, with interchanges at both High Street and Marmion Street connecting to Stirling Highway, as part of the 5-kilometre Roe 9 extension.

However, there are currently no plans for a final stage to take the freight link into North Fremantle and the port.

"There is no Roe 10," Mr Barnett said.

"We are not tunnelling under the [Swan] River, we are not building super bridges over the river."

The tunnel promise marks a turnaround on stage two of the freight link by Mr Barnett.

Then-WA transport minister Dean Nalder backed the tunnel option more than two years ago in a bid to prevent the demolition of homes in the area, just months before a leaked report also advocated the proposal.

Colin Barnett says the freight link is now "fully defined", despite the final stage remaining uncertain. ( ABC News: Andrew O'Connor )

However, Mr Barnett shelved stage two just months later, describing it as "incredibly complicated, incredibly expensive for what it does".

That prompted the Federal and State Governments to renegotiate a billion-dollar deal for the project, with the Commonwealth insisting the freight link must be built in its entirety.

The Commonwealth then committed $260 million to a tunnel in April last year, taking its overall commitment to the freight link to $1.2 billion.

The promise also reinforces a distinct difference between the WA Liberals and Labor in the run-up to the state election in March, with the Opposition vowing to stop work on Roe 8 and the entire freight link if it wins power.

The tunnel would be built from the Stock-Winterfield Road intersection to High Street in East Fremantle. ( Supplied: Main Roads WA )

Tunnel the cheapest option: Barnett

Mr Barnett said construction of Roe 9 was expected to start in 2020, after the completion of Roe 8.

He said the tunnel option was the most direct route, offered better value for money than a surface route, minimised impacts on private property and delivered higher productivity benefits for the freight industry.

"Work is yet to be done on the exact design of that tunnel, there are environmental studies and whole lot to happen," he said.

"It will take around 7,000 heavy trucks off suburban roads. This project will saves lives, simple as that.

"I understand that people object to Roe 8, but I think that the vast majority of people in the southern suburbs will realise that this project is now finally defined.

"People understandably were worried about would their houses get resumed. That is now resolved."

Transport Minister Bill Marmion said Roe 9 would generate 1,900 direct jobs with a total onsite workforce of up to 6,640 during construction.

He said a re-elected Liberal National Government would commit $181 million to the project, with the remaining 80 per cent being provided by the Commonwealth Government.

Mr Marmion said the Roe 9 route from Stock Road to Canning Highway would be subject to a strict environmental approval process, expected to take up to 18 months.

Greens, Labor condemn 'completely failed plan'

The Greens criticised the announcement and called on the State Government to release its business plan for Roe 9, saying Commonwealth funding would not be forthcoming otherwise.

"This plan will cause traffic chaos at North Fremantle," Greens MLC Lynn MacLaren said.

"Barnett is exposing himself to voter backlash from his own electorate with his decide-announce-defend ad hoc policy on-the-run approach.

Roe 9 was originally designed to run along Stock Road and Leach Highway to Stirling Highway. ( Supplied: Main Roads WA )

"The Liberal Party have seen the writing on the wall, the protests at the Beeliar Wetlands are working and public sentiment is shunning Colin Barnett for his completely failed plan for our transport needs.

"Until the Federal Government sees a project proposal report for Roe 9, the WA taxpayer will foot the bill for Roe 8."

WA Labor leader Mark McGowan said the Government was "making it up as they go along".

"Mr Barnett has been all over the place with this project, he's flipped and flopped and then done it again," he said.

"They are blowing $2 billion on a road to nowhere that doesn't fix the problem ... It's going to mean a massive bottleneck in East Fremantle.

"Our plan is to use that money more wisely on projects that make a real difference to congestion around Perth."