Liza Harvey got raucous applause off the Liberal Party faithful when she vowed to them that a government led by her would end decades of debate and kick on with extending Roe Highway.

"It is glaringly obvious that this critical piece of infrastructure needs to be built," she told the Liberal Party's state conference late last month.

"Speak to anyone living in Riverton, Willetton, North Lake, Melville, Palmyra, Jandakot, Atwell, all of those southern suburbs, they have to put up with congestion like no other commuter in Western Australia."

The Liberal Party faithful's delight at that commitment would have been understandable to many.

Almost every Liberal is convinced the Perth Freight Link, a heavy-haulage extension of the existing Roe Highway to Fremantle, is a big potential vote-winner for them.

Polling commissioned by the Liberals earlier this year found 70 per cent of residents in the Melville and Cockburn council areas wanted Roe 8 and 9 built, fuelling belief among their ranks that the $2 billion road is their ticket to winning back key southern suburbs seats lost to Labor two years ago.

Ms Harvey hit the airwaves the next day in a bid to sell the public on her flagship policy, but it did not all go to plan.

Harvey fumbles key details

The Liberal leader said the freight industry had given its support to a truck toll to help pay for the road, a claim quickly dismissed by WA's two most prominent road transport groups.

She was asked for exact details on what the toll would be, but could not provide them.

And Ms Harvey was asked whether there would be a tunnel, a question she was unable to answer clearly.

"I believe there was a tunnelling component to it but Dean [Nalder] is more across those issues because he was the transport minister at the time," she told radio station 6PR.

The Roe Highway extension plans prompted protests against the destruction of wetlands. ( ABC News: Andrew O'Connor )

Since the awkwardness of that situation, Ms Harvey has largely stayed out of the spotlight.

She made a brief speech talking up the project in State Parliament this week, but she has planned just one press conference in the fortnight since the Roe Highway announcement — about crime in Mandurah.

'A really, really bad start'

The lack of effort to get the leader into the public eye has left some Liberals bemused.

"She has had a really, really bad start as leader," one Liberal MP conceded this week, pointing also to the defection of Geraldton MP Ian Blayney as well as confusion and controversy over early policy stances Ms Harvey took on Western Power, retail trading hours and public sector wages.

"They are hiding her."

While the Roe 8 announcement has not delivered the bang for buck some Liberals had hoped for, the party is still convinced it is a big vote-winner.

Shadow transport minister Libby Mettam said the feedback she had received was "overwhelmingly positive" and that there was strong support for the project, not just in the immediately affected suburbs.

"It is a significant community concern," Ms Mettam said.

"This Government has no viable solution for the southern suburbs."

Powerful allies flex muscle

The state Liberals have some powerful allies on their side, with some sections of the media spruiking the pro-Roe case and the Federal Government leaving $1.2 billion on the table to build the project.

The Morrison Government's commitment to the project was made abundantly clear this week.

A joint press conference to mark a suburban road upgrade turned awkward when Urban Infrastructure Minister Alan Tudge used the event to spruik the Freight Link — all while fierce opponent and WA Transport Minister Rita Saffioti stood next to him.

The Liberals are convinced building Roe 8 will be popular among voters in Perth's south. ( ABC News: Andrew O'Connor )

Labor points to its wins in the state seats of Bicton and Jandakot as evidence that the public never wanted Roe 8 or 9, and the party is bullish about fighting another election on it.

The Government believes its decision to divert funds to other projects has delivered far more benefits than the Freight Link would have.

But, despite the substantial missteps of the past fortnight, the Liberals are convinced the road could be their route back to power.