The cost of the first three stages of the F6 Extension is put at more than $9 billion. Credit:John Veage These arrangements are supposed to protect the government from private investors pocketing all of the windfall profits from toll roads in the event that traffic volumes turn out to be significantly higher than forecast. "The analysis indicates the revenue increase is not sufficient to trigger the upside-sharing regimes and therefore RMS would not receive any benefit from the uplift in patronage," the document states. The business case prepared by Roads and Maritime, obtained by the Herald, advises the government to consider options to "balance value creation" between WestConnex and tolls for the F6 Extension. "Alternatively, the state should ensure that potential upside is otherwise captured through any sale of the WestConnex entities," it says.

Under the plans mirroring those for WestConnex, tolls for each of the three sections of the F6 Extension will range from about $3.50 to $3.80 – capped at just over $8 for a one-way trip along the entire motorway – in today's dollars and rising annually at the rate of inflation or 4 per cent, whichever is greater. The state's roads agency has the task of overseeing the design, construction and operation of the F6 Extension, the first stage of which will extend from the WestConnex toll road at Arncliffe to Kogarah in Sydney's south. The cost of building the first three stages of the F6 Extension between Arncliffe and Loftus near the Royal National Park has been put at more than $9 billion. Martin Locke, an adjunct professor at Sydney University and a former investment banker and infrastructure adviser, said upside-sharing arrangements were designed to ensure the state gained a portion of windfall profits made by investors in toll roads. "If the government moves forward with the F6, the increased traffic will create extra revenue for the investors in WestConnex," he said.

"The government will want to have some share in that upside, rather than 100 per cent going to the WestConnex investors." The leaked document shows the government will gain a 30 per cent share in extra revenue from WestConnex only when the amount generated by tolls surpasses 130 per cent of that forecast in the business case for the project. In contrast, the state will gain an "upside share" in the revenue from the NorthConnex tunnel, under construction between the M1 and M2 in Sydney's north, when it is more than 110 per cent of "base revenue". A spokesman for Treasurer Dominic Perrottet said the business case for the F6 had not been finalised, and the government did not comment on "speculation about traffic or revenue forecasts on projects that are subject to ongoing development". The leaked document also reveals that the roads agency will have to pay tens of millions in compensation to the owners of WestConnex if the F6 is "other than a tunnel and surface road connection" from the new M5 at Arncliffe to Kogarah.

Loading In October, Premier Gladys Berejiklian committed to building the first stage of the F6 Extension but declined to release details about the design, cost and tolling, saying such specifics would be provided in mid-2018. The state government wants to complete the sale of a 51 per cent stake in Sydney Motorway Corporation, the corporate entity set up to oversee the building, financing and operation of WestConnex, by the middle of next year. The spokesman for the Treasurer said the government would "continue to provide information" on the sale as the process progressed. The inclusion of tolling revenue from existing motorways such as the M5 South West and a widened section of the M4 between Homebush and Parramatta will help improve the attractiveness of Australia's largest motorway project to large private investors.