Decision time is rapidly approaching on the future of the 10.5km North-South road corridor between the River Torrens and Darlington

Decision time is rapidly approaching on the future of the North-South Corridor – and 6km of tunnels under Adelaide is looking more and more remote as costs soar.

Decision time is rapidly approaching on the future of the state’s biggest infrastructure project, the $9.9bn, 10.5km North-South road corridor between the River Torrens and Darlington.

The prospect of more than 6km of tunnels underneath Adelaide’s western suburbs is looking more and more remote as costs soar.

Instead, there are likely to be shorter tunnels and more lowered roadways gouged along South Rd’s current route. Acquiring land and excavating a channel to build the motorway – as happened from the River Torrens to Torrens Rd – is likely to be less costly than tunnels. But more land acquisition would ignite anger among affected property owners, creating a political headache.

A project review is expected to be completed – but possibly not publicly released yet – within days. It is understood the end of August was set as the scheduled target for finishing this Infrastructure and Transport Department review, commissioned by the Labor government shortly after winning the March state election.

Almost nine years ago, the-then prime minister Tony Abbott declared he could “get the whole North-South Road Corridor upgraded within a decade” if a state Liberal government was elected. Picture: AAP Image / Ben Macmahon

Already, soaring inflation has sent costs spiralling. The Advertiser in late June revealed the $9.9bn forecast cost had swollen to about $14bn. It was also understood a cost-benefit analysis returned a ratio of less than one – an industry measurement meaning the costs outweigh the benefits of going ahead.

Two months later and The Advertiser has been told the project costs, depending on the options, range up to $15bn.

Senior business figures are questioning the economic benefit of an expensive road that might make commuters’ lives easier but might not be worth the huge money. After all, what sensible business or government would pour money into an investment that returned less than it cost? Cabinet ministers are aware of this criticism and the risk to the state’s finances.

South Australian MP Jamie Briggs, former Australian Prime Minister Tony Abbott, former SA Premier Jay Weatherill and MP Stephen Mullighan sod turn, Wednesday, Aug 5, 2105. Picture: AAP Image / Ben Macmahon

At his June 2 state budget press conference, Treasurer Stephen Mullighan declared he wanted the North-South corridor and the $2.1bn new Women’s and Children’s Hospital projects “delivered as quickly as possible” – before costs inflated still further and added to net debt already forecast to increase to almost $34bn by 2025-26

“My challenge is to limit any further debt increase beyond those two projects as much as possible. And the challenge for the Cabinet, particularly over the next two years, will be to recalibrate how much our spending is growing each year, and how much our infrastructure spending will be in those years of those two projects being on the state’s books,” he said

Infrastructure project costs are soaring. The Australian Constructors Association on July 28 released a report citing examples of price rises of up to 70 per cent over a 12-month period, cautioning against governments trying to escape the problem by delaying or deferring projects and warning “the industry cannot continue to bear the cost of these steep price increases”.

Inflation has taken off since the mid-February pledge that the motorway was fully costed – delivered by the-then prime minister Scott Morrison when he unveiled a $2.26bn boost for the corridor alongside the-then premier Steven Marshall. At the time, the plan was for two stages. The first, which had been due to start next year at a total cost of $5.422bn, involved building 4km-long tunnels connecting Darlington to Anzac Hwy.

Tony Abbott, pictured with former Premier Steven Marshall, visits the corner of South Rd and Sturt Rd to make an infrastructure announcement.

The second, $4.48bn stage involved more than 2km of tunnels from Torrensville from 2026. Both tunnels were to be joined by a lowered, twin three-lane motorway, allowing non-stop travel from Gawler to Old Noarlunga. Compulsory acquisitions were set at 393 properties.

Almost nine years ago, the-then prime minister Tony Abbott in October, 2013, declared he could “get the whole North-South Road Corridor upgraded within a decade” if a state Liberal government was elected in 2013. But Labor was returned and Mr Mullighan, as transport minister, forged a bipartisan alliance with SA federal Liberal minister Jamie Briggs to in August, 2015, leverage $1.5 billion for two major parts of the corridor — the Torrens Rd to River Torrens section and Darlington section. In one of his final acts as prime minister, Mr Abbott in September, 2015, tipped in $788m to kickstart the $985m Northern Connector, linking the Port River and Northern expressways and South Rd Superway. The connector opened to traffic in March, 2020.

Since then, there’s been plenty of talk and not much action. Mr Abbott’s vision of a non-stop motorway by 2023 will not be realised. If cost pressures result in changes to smaller tunnels and more property acquisitions, at least there would be a cheaper motorway. But is the political and debt cost still too much to bear?