The planned toll road linking Sydney and Wollongong has been costed at an extraordinary $18 billion – almost $12 billion more than the rail alternative that would cut the journey to about one hour.
The cost of the F6 Extension, which is also greater than the $16.8 billion estimate for WestConnex, is revealed in government documents seen by Fairfax Media and the ABC that raise doubts about the government's ability to build both projects at the same time.
Described as the "Gateway to the South" in the cabinet-in-confidence document seen by Fairfax, the 32-kilometre road would extend from a Westconnex junction at St Peters to President Avenue in Monterey via a nine-kilometre tunnel followed by a continuous tunnel along the Sandringham Peninsula to the Georges River at San Souci.
It would then travel above ground from Taren Point to Loftus and then through or adjacent to the Royal National Park to Waterfall, where it would connect with the Princes Highway.
A Roads and Maritime engagement and communication plan seen by Fairfax Media says messaging on the national park would need "careful management". Should the government be unable to run the expressway through the national park, it would need to acquire and bulldoze about 500 homes and commercial properties.
The document estimates the construction cost at $14.5 billion. A separate document puts operation and maintenance costs at $3.5 billion.
The $18 billion total raises questions about whether the road will ever be built. Fairfax Media understands that negotiations on a public-private partnership on cost sharing are advanced.
A spokesman for Roads Minister Melinda Pavey said the F6 Extension was in an early development stage.
"No decision has yet been made regarding the final alignment or form of the proposed F6 Extension, therefore it is too early to speculate on the final cost," he said.
Greens NSW transport spokesperson Mehreen Faruqi called the $18 billion price tag "madness".
"Eighteen billion dollars of taxpayers' money for yet another toll road, potentially through a national park, is just obscene," she said.
The cabinet-in-confidence costing lends weight to a claim in a separate Transport for NSW report released under the Government Information (Public Access Act) that the difference in cost between the road and rail options would be "sufficient to construct the equivalent of almost three Snowy Mountains Hydro Schemes".
The Snowy Mountains scheme is thought to have cost around $5 billion in today's dollars.
The rail alternative would be made up of a separate Maldon to Dombarton freight line to enable coal trains to be taken off the Illawarra line, the construction of a tunnel at Thirroul and extra rolling stock.
The June budget allocated $15 million for planning work for the extension on top of $20 million for geotechnical testing in December.