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Frequently asked questions

Project details, timeline and status

What is the North-South Corridor?

The 78 km North-South Corridor will unlock Adelaide’s transport network by providing a non-stop traffic-light-free connection between Gawler and Old Noarlunga, with links to the port and airport precincts. The corridor consists of the following sections of non-stop motorway:

  • Southern Expressway
  • Darlington Interchange
  • Torrens to Torrens
  • South Road Superway
  • Northern Connector
  • Northern Expressway

The Australian and South Australian governments are getting on with completing the final sections of the corridor including the $354 million Regency Road to Pym Street Upgrade, due for completion in early 2022, and the final and most complex section between the River Torrens and Darlington, the Torrens to Darlington Project (T2D).

What is the Torrens to Darlington Project?

The Australian and South Australian governments are delivering the 10.5 kilometre T2D Project, which is the most complex section of the North-South Corridor due to the ground conditions, unique heritage assets and social character of the surrounding area.

A hybrid+ option will see a combination of tunnels, lowered and ground-level motorway, as well as overpasses / underpasses at key intersections (to be defined during the design refinement) to successfully complete the non-stop, traffic-light-free transport route. When complete, around 60% of the T2D Project will be underground tunnels.

This final section will be delivered in the following stages:

Southern Tunnel: Linking Anzac Highway to Darlington

  • Approximately 6 km of motorway including over 4 km of tunnel to address this very congested section of South Road
  • The construction program will prioritise minimising disruptions to motorists, residents and businesses along this section of South Road
  • Pending relevant approvals, construction is expected to commence in late 2023 and take approximately 4-5 years
  • Stakeholder engagement on this project is underway. To sign up for updates please register your details on the project’s website: www.dit.sa.gov.au/torrenstodarlington

Airport Link and Northern Tunnel: Linking River Torrens to Anzac Highway

  • Engagement, planning, early works, procurement and approvals will run concurrently to the Southern Tunnel
  • Construction is expected to commence in 2026, subject to planning, approvals and funding
  • Completion of the final 10.5 km section expected in 2030

Why is it being delivered in stages?

By delivering the project in stages, sections can be opened as they are completed, while other parts continue being constructed concurrently. This staged approach is commonly used in complex infrastructure projects.

The first stage of the project, the Southern Tunnel, will consist of approximately 6 km of motorway, of which over 4 km will be tunnel. This stage will connect Anzac Highway to Darlington.

The second stage of the project will link the River Torrens to Anzac Highway with an at-surface Airport Link and the Northern Tunnel.

Why is the hybrid+ option preferred to deliver this section?

The hybrid+ design is the best option to deliver the key benefits of the project, whilst:

  • Improving safety and reliability for road users by bypassing 21 sets of traffic lights
  • Minimising community and business impacts by saving 480 more properties and reducing the number of business closures by 40% when compared to the open motorway option
  • Minimising, heritage and social impacts
  • Maximising the city shaping opportunities
  • Maximising the property value uplift
  • Removing more than 110,000 vehicles at Thebarton and Edwardstown minimising the number of vehicles and helping to enhance the feel and look of the areas along South Road
  • Providing more efficient links between key industry and freight routes of the National Land Transport Network, the Port of Adelaide, Adelaide Airport, the city’s manufacturing and industrial precincts, and the northern and southern regions of South Australia
  • Enhancing community connectivity by reducing infrastructure barriers

Many years of extensive investigations and analysis of traffic data, ground conditions, local environment, heritage assets, and stakeholder feedback as well as numerous independent evaluations and reviews, have confirmed that a hybrid+ option will deliver the greatest transport, social and economic benefits for the community and the state.

Compared to other options, the hybrid+ solution will more effectively reduce the number of vehicles using South Road each day, thereby providing a unique, once-in-a-lifetime opportunity to reshape and enrich the surrounding areas through a dedicated City Shaping program.

Were any other options to deliver the project considered?

In addition to the preferred hybrid+ option, a number of alternative models were also investigated and analysed. These options failed to match the hybrid+ design in meeting key social, economic, heritage, safety and environmental objectives:

Open Motorway

  • This was one of the final two design options but was not recommended for a number of reasons
  • Compared to the hybrid+ option, an open motorway would have ignored the concerns of the majority of the community, and imposed a ten-lane-wide asphalt and concrete wedge along South Road
  • One of the key reasons for choosing the hybrid+ option was its capacity to minimise the number of houses, businesses and community facilities that may need to be acquired
  • While it is not possible yet to identify exactly which and how many properties will need to be acquired under the hybrid+ option, it is estimated that it would reduce the number of acquisitions by 480 properties when compared to the open motorway option
  • By significantly impacting homes, businesses and heritage sites, the open motorway would have not met one of the key project objectives to improve community connectivity
  • Compared to the hybrid+, this option more than doubled land acquisition
  • This option, would have significantly increased traffic noise at Thebarton and Edwardstown when compared to the hybrid+ design

Single Long Tunnel

  • One long, continuous tunnel was contemplated when the tunnel concepts were re-introduced in 2018
  • After analysing how drivers make use of South Road and the surrounding network, it was clear this option failed to provide convenient and adequate connections to Adelaide travel destinations
  • This lack of accessibility would have decreased the number of drivers using this route, and therefore offered limited overall benefit to Adelaide’s transport network and would not alleviate the congestion on South Road

Dual Corridor

  • A dual-corridor concept was proposed, using both South Road and Marion Road, with grade separations such as overpasses and underpasses at key intersections, and a short tunnel connecting the northern end of Marion Road to the southern end of Torrens Road to the River Torrens
  • By utilising existing major arterial roads, this option would:
    • Fail to deliver a non-stop transport corridor
    • Fail to increase the network capacity to address current congestion
    • Fail to improve efficiency and network reliability
    • Fail to provide opportunities for city-shaping and urban uplift
  • The dual corridor option would also limit speeds to 60 km/h and require extended clearways along two major commercial roads
  • The effects of this option would have seen a significant departure from the objective of providing a seamless, efficient, and free-flowing, north-south motorway connection

Cut and Cover Tunnelling Construction

  • As its name suggests, ‘cut and cover’ involves cutting a long, deep channel to accommodate the motorway, and then covering it with a concrete deck to effectively create a motorway tunnel
  • Cut and cover construction was considered as an alternative to using tunnel boring machines. However, when compared to the recommended hybrid+ option, cut and cover construction would have required a wider road corridor, and more than twice the number of compulsory property acquisitions
  • The open-channel construction would have led to extensive and costly relocation of power, communications, gas, water, sewer and service infrastructure. It would also have meant lengthy traffic disruptions and road closures
  • The impact of construction dust and noise to local communities, together with the estimated cost being, for this length of tunnelling, around 30% higher than using Tunnel Boring Machines, suggested this option was neither viable nor appropriate

Elevated Motorway

  • An elevated motorway option was also evaluated during the planning studies and in terms of the economics, performed poorly
  • Technical analysis showed that this approach would require widening the current South Road corridor, resulting in over 1,000 properties being directly impacted by acquisition as well as the visual amenity of remaining properties being severely compromised
  • During initial engagement prior to 2018, the community ranked this design as the ‘least preferred’ option

What stage of development is the T2D Project up to?

Following the decision to proceed with a hybrid+ option, our team are now working to ensure we have the best plan in place to minimise impact to properties, and deliver the safest, most reliable motorway possible.

The next stage in the project’s development is to produce a Reference Design and Final Business Case which are both expected to be completed in the second half of 2021.

Development of the Reference Design will be informed by more detailed technical investigations and engagement with the traditional owners of the land, residents, businesses, the community, road-users, businesses, and industry to better understand their views.

What is the Reference Design?

The Reference Design sets minimum design standards and provides guidance to designers of each stage of the project.

These design standards include desired project outcomes, engineering requirements, and environmental and social assessments.

When will construction commence?

As a decision to proceed with a hybrid+ option has now been approved, the project will progress to the next stage of development. This includes ongoing ground investigations, detailed design and a comprehensive stakeholder engagement program.

The Southern Tunnel linking Anzac Highway to Darlington is expected to commence construction late 2023 and will take approximately 4-5 years.

The central section between the Southern Tunnel and the Northern Tunnel will be a combination of lowered motorways at key intersections and at-grade surface roads.

The second stage of the project will link the River Torrens to Anzac Highway with an at-surface Airport Link section and the Northern Tunnel. Construction of the second stage is expected to start in 2026.

What works are currently occurring on site now?

A ground investigations program, including geotechnical and hydrogeological testing, is underway to help us build on our current understanding of the underlying soil and groundwater conditions along the final section of the North-South Corridor.

The ground investigations drilling program for the entire T2D Project is well underway. The first part of the ground investigation program is due for completion the second half of 2021, these investigations are part of a broad range of works that shape the project, ensuring the solution will meet the needs of South Australians for decades to come.

By the end of February 2021, we would have completed nearly 5,000 tests, across 200 testing locations (holes).

To undertake these critical investigations, a specialist crew sets up a drill rig site to conduct the testing. This will generally involve:

  • Implementing temporary local traffic management
  • The presence of personnel and light vehicles
  • Minor excavation to uncover any underground services in the immediate area
  • Drilling a bore hole to collect ground samples
  • Performing a range of tests
  • Restoring the rig site

Work crews will make every effort to minimise disruption and noise, and following completion of each test, the site will be fully reinstated.

Does the location of ground investigation works indicate what properties will be affected?

The selected locations do not necessarily mean those areas will be impacted by construction, but rather, they have been carefully chosen to minimise impacts to road users, businesses and residents, while still providing a good understanding of the underlying soil and groundwater conditions.

Project benefits

Why do we need this final section? What’s in it for South Australia?

Currently, more than 110,000 vehicles use parts of South Road and its parallel alternate routes in a north-south direction each day. Further, 100,000 vehicles travel in an east-west direction through key intersections on South Road. With four out of the six key intersections almost at capacity a solution to bust congestion was of critical importance to support South Australia’s growth.

When this section is complete, motorists will be able to travel from the River Torrens to Darlington in around eight minutes, bypassing 21 sets of traffic lights and saving up to 24 minutes in travel time per trip.

The project will also deliver a wide range of social, economic, environmental and safety benefits, not only for Adelaide, but for South Australia, including:

  • Creating up to 4,000 jobs during construction and building a skills legacy for future projects
  • Around 60% of the motorway will be in underground tunnels – meaning less impacts to the surface and communities
  • Removing more than 110,000 daily vehicle movements from Edwardstown and Thebarton into underground tunnels
  • Improving the connectivity of the east-west transport network
  • Better access to travel gateways including Adelaide Airport, the Port of Adelaide, and national highways
  • Safer, more reliable and efficient journeys
    • Bypassing 21 sets of traffic lights
    • Shaving up to 24 minutes off the existing River Torrens to Darlington journey
    • Busting congestion at notorious key intersections
  • Improving South Australia’s competitiveness through the provision of efficient access to and from key freight areas
  • Preserving sites of cultural importance, including:
    • Thebarton Theatre
    • Hindmarsh Cemetery
    • Hoffman Brick Kiln
    • Queen of Angels Church
  • 78 km of non-stop travel from the north to the south of Adelaide
  • Creating opportunities for urban renewal and place-making for local businesses and residents through a dedicated City Shaping Program
    • New and upgraded walking and cycling paths
    • New and improved green spaces and recreational areas
  • Providing better connections, bringing communities together

What are the economic benefits of the T2D Project?

Large transport infrastructure projects generate significant revenue for local and regional economies, stimulate employment opportunities and investment during both construction and operation.

In addition to construction work on site, numerous jobs will also be created in areas such as design, engineering, manufacturing, administration, logistics, trades, security, safety, surveying, finance, legal, HR, environment management, fabrication, health and safety, communications and management roles, both within the project itself and across a wide range of local suppliers and contractors.

What sort of jobs and skills opportunities will there be?

From design to construction, the project will create up to 4,000 jobs. These jobs include plant-operators, concreters, pavers, welders, electricians, pipe fitters, mechanics, engineers, health and safety professionals, to name a few, with the safety and wellbeing of the workforce being the top priority.

The South Australian Government will invest in local people to give them the opportunity to work on the biggest infrastructure project in the state, and build the skills required to work on projects in the future.

How are you protecting Adelaide’s precious heritage sites?

We share the community’s view that progress and heritage can co-exist, and that as many local and state treasures should be preserved as is practically possible.

The preferred hybrid+ option:

  • Saves Thebarton Theatre
  • Saves Hindmarsh Cemetery
  • Saves Hoffman Brick Kiln
  • Saves Queen of Angels Church
  • Minimises impact on land along that section of the corridor
  • Maintains the area’s suburban, neighbourhood character
  • When compared to an open motorway option, all of the heritage sites will be saved, with the potential exception of one. The Reference Design will inform the approach and impacts on this site

Will there be opportunities for urban renewal along the existing South Road?

We recognise that the final project design must help Adelaide retain its status in the top 10 most liveable cities in the world.

The hybrid+ solution will remove over 110,000 vehicles from Thebarton and Edwardstown each day, reducing noise and visual impacts and providing a rare opportunity to reshape and enhance the surrounding areas.

A dedicated City Shaping program will be implemented to provide attractive, well-considered public spaces with urban design, landscaping and greenery designed to enhance South Road.

The T2D Project is not only being planned by South Australians and built for South Australians, but with South Australians. Together, we can shape tomorrow’s infrastructure and transport network; therefore it is critical that we engage widely.

We understand how important some of the features of this historic project are, and commit to engaging with the community.

Our dedicated engagement team will be hosting a number of drop in sessions, the first one expected to take place late November - managed in accordance with the latest health advice to meet COVID requirements. These sessions will be in the vicinity of Torrensville and Edwardstown, and across a range of dates and convenient times.

Project design and features

Where will the tunnels start and finish?

The T2D section will be delivered in stages. This approach means sections can be opened as they are completed, while other parts continue being constructed. This staged approach is commonly used in complex infrastructure projects.

The first stage of the project, the Southern Tunnel, will consist of approximately 6 km of motorway, of which over 4 km will be tunnel. This stage will connect Anzac Highway to Darlington. Pending approvals, construction is expected to commence in late 2023.

Delivery of the Southern Tunnel will provide significant network benefits through the removal of the Edwardstown bottleneck on South Road and improved access to the CBD from the south of Adelaide.

The central section between the Southern Tunnel and the Northern Tunnel will be a combination of lowered motorways at key intersections and at-grade surface roads.

The second stage of the project will link the River Torrens to Anzac Highway with an at-surface Airport Link section and the Northern Tunnel. Construction of the second stage is expected to start in 2026.

Investigation works are currently being undertaken to determine the ground conditions and the exact locations of where tunnels will begin and end. These investigations will inform the Reference Design, and updates will be provided once these are known.

Where will the tunnels connect with surface roads?

It is important we better understand the way South Australians use the transport network as the location for the surface connections is determined by traffic modelling and the demand forecast. This data will inform the key traffic movement and connectivity that our community needs.

It will also determine the optimal areas where the tunnels will connect to the surface roads and allow the most efficient traffic movements and journeys.

What will be the height of the underground tunnel?

The height of the tunnel will be determined by a number of factors, including the number of tunnel lanes required. The number of lanes will determine the diameter of the Tunnel Boring Machines (TBM) in addition to freight and High Productivity Vehicle height needs.

While the diameter of TBMs can vary, it is estimated that the machines we will use will be around 15 metres.

How many lanes will the tunnels be when they open to traffic?

This will be determined as we continue to develop the design, update our traffic modelling and engage with key stakeholders. We expect the tunnels to be built for at least two lanes in each direction. When complete, the Torrens to Darlington Project will more than double the capacity of this section of South Road.

What will the signposted speed be within the tunnels?

As is the case for similar motorways across Australia, we expect the speed limit within the tunnels will be 80 km/h.

How will I know if the tunnel will be near my property?

As we continue to refine the project’s design, we will engage with the community and key stakeholders to ensure they have as much visibility as possible on the project’s development and the location of permanent infrastructure.

How noisy will tunnelling be?

Using tunnel boring machines (TBM) means the tunnels can be constructed below ground-level, reducing disruption above ground.

Properties located near the path of the TBMs may experience low levels of noise or vibration.

In most cases noise on the surface generated by vibration would be no more than 35 dBA (roughly the same noise level inside a private office) during the night at residential locations more than 30 metres from the nearest tunnel. This is around half that of a normal conversation. The highest impact would be as tunnelling work directly passes under a property which would only be for a short period.

However, TBMs are very effective at reducing vibration, so people living and working above may not notice construction happening beneath them.

Stakeholder engagement

How are you engaging with the community?

The T2D Project is being delivered by South Australians for South Australians. Together, we can shape tomorrow’s infrastructure and transport network. Keeping you up to date with our progress as we upgrade the Torrens to Darlington section of the North-South Corridor, is one of our top priorities. The Feedback we receive helps to inform our decisions.

There’ll be many opportunities to get involved and provide feedback on the T2D project. We’ll engage with the traditional owners of the land, the community, road-users, businesses, and industry to better understand their hopes and concerns for the project. We’ll keep you regularly informed through mail and email notifications, social media, our website and other engagement activity.

You can subscribe to receive regular updates at www.dit.sa.gov.au/torrenstodarlington

How will you work to support business through years of disruption?

While any project of this scale has the potential to affect businesses during the construction phase, our aim is to minimise impacts, and deliver positive and lasting outcomes for those located along the project corridor.

A number of initiatives to support businesses during the delivery of this project will be implemented, including:

  • The development of a Business Assistance Program to engage and support businesses
  • Openly discussing ways in which we can help businesses thrive during and after construction

How will you engage with the traditional landowners of the corridor?

The T2D Project team has existing relationships with Kaurna representatives and will work collaboratively with them to develop a comprehensive Aboriginal Engagement plan.

The T2D Project commits to actively encouraging Aboriginal participation in, and benefit from, employment and economic opportunities arising out the completion of the North-South Corridor.

What property acquisition will be required to build the T2D Project?

Around 60% of the T2D project is being built in underground tunnels to minimise impacts on the surface.

As is to be expected in any significant, inner-urban infrastructure project, additional land will be required to accommodate construction of the motorway. One of the key reasons for choosing the hybrid+ option was its capacity to minimise the number of houses, businesses and community facilities that may need to be acquired.

While it is not possible yet to identify exactly which and how many properties will need to be acquired under the hybrid+ option, it is estimated that it will reduce the number of acquisitions by 480 properties when compared to the open motorway option.

The location of affected properties will be established as detailed planning continues and the Reference Design is finalised in the second half of 2021.

Once the Reference Design is finalised, we expect to be in a position to engage with stakeholders who have an interest in land which will be impacted by full or partial acquisition. These discussions will include clear and transparent details about the land acquisition process, and will allow all parties to work together in a transparent and collaborative manner.

Where the tunnels pass under properties, the property at surface level is generally not required for acquisition.

What about residents living next to construction sites for years?

In order to create a path for the T2D additional land will be required. Following on from an extensive planning process that will include government approvals and funding, the Department for Infrastructure and Transport (the Department) will make a determination regarding land requirements. The Department will contact all parties with an interest in land to discuss the land acquisition process.

How much is the T2D Project going to cost?

The Australian and South Australian governments have committed to delivering the non-stop North-South Corridor for Adelaide.

The Australian and South Australian governments have already committed $4.8 billion to delivering projects on the North-South Corridor, with a further $5.4 billion towards delivering the T2D Project.

The T2D Project is in the early planning stages and further refinements to costings will be determined during the development of the Reference Design and Final Business Case. Costings for the project will be further defined and contracted as part of the construction procurement process.

The South Australian Government will continue to work with the Australian Government and with Infrastructure Australia to ensure the completion of the North-South Corridor remains a priority project.

How do I find out more?

Please contact our dedicated team via:

Website:         www.dit.sa.gov.au/torrenstodarlington

Phone:           1300 951 145

Email:             northsouthcorridor@sa.gov.au

Facebook:     @DFITSA


You can register your details with the project team for updates and provide comments, click here.