Cost of Torrens to Darlington project blows out to more than $15bn in designs to be revealed by state government

Revised designs for the Torrens to Darlington project are set to be revealed by the state government on Wednesday after a lengthy review.

New Torrens to Darlington concept images show the southern entrance to the southern tunnel. Picture: Supplied by SA Government

Revised designs for the Torrens to Darlington project, set to be revealed by the state government on Wednesday after a lengthy review, will cost upwards of $15bn to complete.

The new designs will retain twin northern and southern tunnels along the 10.5km stretch of road, and will require the acquisition of more than 412 properties.

The project remains on track for completion by 2031.

The review, which was independently audited by firm PwC and tested against alternative options, found the $9.9bn business case released last year by the former Liberal government was “significantly understated and underscoped”.

A new Torrens to Darlington concept image. More details will be released by the government on Wednesday. Picture: Supplied by SA Government

It found if the project was completed as presented, it would instead have cost $14.3bn – but it did not account for “broader network upgrades” that were essential for the effective operation of the motorway.

Incorporating those upgrades, the review found the Liberals’ 2021 plan would have cost a total $15.15bn.

But it is understood the new design, to be revealed by Transport Minister Tom Koutsantonis, will come at an even higher price. It was unclear on Tuesday how Labor’s design would differ from the previous plan.

The PwC review also found that the true number of full and partial acquisitions required to deliver the Liberals’ plan would be 412 – 19 more than the 393 announced by the former government.

However, it is understood more properties will need to be acquired to accommodate the latest changes.

Mr Koutsantonis has previously flagged his intention to remove elevated roadways at Anzac Hwy and West Hindmarsh, which had proven unpopular with local communities. PwC’s financial audit also provided cost breakdowns for two other roadway solutions as a comparison. These included the “Open Motorway” option, a combination of below-grade “open” motorway and above-ground structures, which was found to have an estimated total cost of $14.5bn and would have required 813 property acquisitions.

The audit found the “at-grade” motorway option would have cost an estimated $12.8bn and required 867 acquisitions, including the Thebarton Theatre, St Anthony’s Church and Hilton and West Thebarton hotels.

It found that if the $9.9bn budget was maintained, only the southern tunnel section of the original reference design could be delivered.

Mr Koutsantonis said it was vital to do the project “right first-time”.

On Tuesday, the opposition accused the government of trying to “stem any political damage” after 10 job advertisements for “engagement specialists” were posted online last week. However, a government spokesman said the roles already existed within the department’s structure and only five related to the North-South Corridor.