State Government seriously considers multi-billion dollar twin tunnel solution for Adelaide’s traffic woes

Two separate traffic tunnels bored beneath South Rd are being seriously considered by the State Government as the multibillion-dollar fix for Adelaide’s major motorway — SEE THE DESIGN.

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Two separate traffic tunnels bored beneath South Rd are being seriously considered by the State Government as the multibillion-dollar fix for the city’s major motorway.

The Sunday Mail can reveal designs for the possible engineering solution, which it is hoped could avoid the need for huge expense and disruption by buying up properties on the surface.

The so-called “hybrid tunnel” solution would feature one underground stretch between the River Torrens and Anzac Hwy, where traffic would return to using existing infrastructure including under and overpasses, before going below ground again from Edward St to Tonsley.

The Government is also considering one super-tunnel from the completed Torrens to Torrens project to the Darlington Upgrade now underway, and a surface-level option.

However, indicative timelines provided by the Department of Planning, Transport and Infrastructure suggest major construction may not be finished for another decade.

Transport Minister Stephan Knoll said a decision on the best path forward would be taken this year, and the Government would chose the best option rather than the cheapest.

River Torrens to Darlington Project — North-South Corridor project.

He said a tunnel could cost more, but create less disruption for residents and businesses.

“When we were looking at a long tunnel, it became apparent that a hybrid tunnel could deliver a better balance of traffic flows,” Mr Knoll said.

“There was a suggestion that other arterial roads could have all their traffic sucked up into South Rd, creating more bottlenecks.

“We need to distribute the traffic well, and the hybrid tunnel is a possible solution.”

Designers also believe the twin tunnels option will allow more people to get on and off the rebuilt South Rd, rather than it being commonly used as an express route for 10km.

Mr Knoll said the Government was “very keen in the decision making to factor in what this is going to mean for businesses and communities along that corridor”.

The Government will receive a final business case in the coming months.

It has not released cost estimates, but the price tag is expected to total several billion dollars.

The Government last year committed to the Regency Rd to Pym St upgrade, which will complete a 47km non-stop free flow roadway between Gawler and the River Torrens.

The area between Thebarton and Oaklands Park is the last piece of the puzzle in completing a non-stop South Rd and follows major builds including the northern and southern expressways.

A South Rd planning study released by the Federal Government in 2015 estimated a cost of $596 million for land purchases alone before heavy construction could start on upgrading the road from Gallipoli Underpass to Darlington.

A further $375 million was estimated to buy land north of Anzac Hwy so work could start to reach the Torrens to Torrens upgrade.

A concept image of the River Torrens to Darlington Project.

A concept image of the River Torrens to Darlington Project.

Federal Cities, Urban Infrastructure and Population Minister Alan Tudge said finishing a non-stop South Rd from Gawler to Old Noarlunga would “make a huge difference” for Adelaide.

“It’s been truly fantastic to see the Marshall Liberal Government working hard on the business cases for the remaining stages, which will be the most complex,” he said.

“They are progressing well so we can get on with delivering the final section and get people home sooner and safer.”

Former prime minister Tony Abbott in 2013 said he wanted to finish South Rd in a decade.

SA Opposition transport spokesman Tom Koutsantonis said that timeline was set to be “blown out of the water”, and state Liberals had failed to secure the cash to deliver the build.

“South Australians just can’t trust what the Commonwealth promises on South Rd,” he said.

“We were told, when Premier Steven Marshall was elected, that he’d have a better relationship with the Federal Government. That’s turned out to be very much a one-way relationship.

“Whether it’s the River Murray or South Rd, it’s being done on the Commonwealth’s terms.”

Mr Koutsantonis also raised concerns about how the state component of the build would be funded, given Mr Marshall’s first Budget included a significant increase in SA’s forecast debt.