Close to 1,000 people turned up to protest a big new road in Perth this weekend.

Hundreds marched through Fremantle to voice their distaste for the WA Government's $1.6 billion Perth Freight Link project.

The heavy transport route is designed to link Perth's industrial eastern suburbs to the Fremantle Port, improving the transfer of goods and bringing a range of economic and employment benefits.

But the road is opposed by residents who could lose their homes to make way. 

There was also a strong showing from conservationists, who argue that a crucial link attaching the Roe Highway from the Kwinana Freeway to Stock Road, will damage the nearby Beeliar Wetlands.

The state’s Labor Opposition has used a recent Infrastructure Australia report (PDF) – which showed the project was hastily-conceived - to argue against it.

The report said the WA Government's business case “outlines strong links” with state priorities and policies, but that “at the time of the assignment (May 2015), the Perth Freight Link is not directly mentioned” in eight key strategic planning documents.

Infrastructure Australia says the freight link was picked from a shortlist of four proposals, which was itself cut from a list of 12 options.

Butof the 12 options, only the Perth Freight Link underwent any detailed assessment.

“A rapid BCR (Benefit Cost Ratio) was not completed for additional options to determine if the preferred option provided the greatest net benefits,” it said.

While the report questioned some modelling used to justify the project, it concluded that it was likely to deliver economic benefits.

The Opposition says it would immediately allocate money towards a study into a new outer harbour at Kwinana if it won the next federal election.

But WA Transport Minister Dean Nalder maintains that the project is well-planned and environmentally responsible, calling it “a fantastic project and a very important project for shifting freight,” at the opening of a Gateway WA project interchange on the weekend.

“At the moment the number of trucks that are growing on Kwinana Freeway and intermingling with passenger vehicles is very large.

“With the Roe 8 section it takes it across to Stock Road, which will service both the inner harbour and the outer harbour when it's developed.

“We understand there's concerns whenever we do something that impacts on natural vegetation, we need to make sure we've looked at it carefully, we followed due-process, and I'm very comfortable the process has been done properly and we're doing the right thing and the responsible thing for Western Australia.”