Private car users would save $1 billion in reduced travel time if the Perth Freight Link were built, a partial analysis has found.
Released to the Senate after pressure from the Greens and Labor, the figures compiled by Main Roads claimed the biggest saving from the $1.6 billion project would be those associated with running vehicles, including reduced wear and tear on tyres.
The project, which would be a traffic light-free link between Perth Airport and Fremantle port, was one of the centrepiece infrastructure announcements in the Government's first Budget.
Heavy vehicles would pay a toll to use the road. The Government had claimed a cost-benefit analysis of the project showed that for every dollar invested, the economy would be $5.20 better off.
But the partial report released to the Senate shows it is not a full cost-benefit analysis. Instead, the figures are based on a Main Roads "rapid benefit cost ratio".
The Roe Highway extension part of the project would generate $4.3 billion in total savings, including $1 billion in time savings to private car users, $1.7 billion in savings from reduced vehicle operating costs, $1 billion in reduced travel times for commercial vehicles and $520 million in accident savings.
The same partial report suggests that improving High Street and Stock Road will deliver $1.4 billion in benefits but at a much-reduced cost-benefit ratio of $1.70 for every dollar invested.
WA Greens senator Scott Ludlam said the Government was hiding the full cost-benefit analysis.
"It looks like they've pulled some numbers together to justify a project that nobody wants," he said.