Due to the size and scale of the T2D Project, a project-specific sustainability approach and assessment methodology has been adopted seeking to move beyond a 'business as usual' approach. The Department seeks to proactively identify and maximise opportunities to deliver positive environmental, social and economic outcomes. This will leave a larger, more positive legacy of sustainable and connected communities.

As part of this approach, a sustainability commitment and associated requirements have been developed incorporating impact and opportunity areas identified during the project’s planning phase.

This commitment will inform contract and procurement documentation and will increase positive outcomes by:

• fostering future-ready and resilient infrastructure and communities
• protecting and enhancing the local environment and communities
• integrating and embedding sustainability through developing measurable targets in project decision making and the supply chain.

The assessment of sustainability impacts and opportunities of the T2D Project was based on technical investigations that have been prepared as the project design evolved.

The key technical document to date for the project is the Planning Phase Sustainability Plan which has been prepared in accordance with the Department’s Sustainability Manual (SM), Master Specification (MS) and Transport Planning Investigations Frameworks. Due to the size and complexity of the project, a bespoke Sustainability MS has been developed which incorporates and builds on PC-ST1 – Sustainability in Design and PC-ST2 – Sustainability in Construction.

The technical investigations that relate to sustainability impacts and opportunities of the project that were considered by the Department in this assessment include:

• Planning Phase Sustainability Plan which outlines the approach to implementing sustainability through contract requirements and includes high-level greenhouse gas emissions estimates and circular economy assessment
• Preliminary Climate and Natural Hazard Risk Assessment
• Urban and Landscaping Design Plan
• Ground and Surface Water Strategy.

These technical investigations are summarised in the Impacts and mitigation measures section.

The T2D Project will create both positive and negative environmental, social and economic outcomes in areas of the project due to its magnitude and complexity. Impact and opportunity areas were identified early in the planning phase and are presented below.

The sections following the table summarise the sustainability assessments completed for the key impact areas considered during Project Design, which provide the basis for development of sustainability initiatives and opportunities.

Key sustainability impacts and opportunities

Greenhouse gas emissions

As part of the Planning Phase Sustainability Plan, high-level whole-of-life greenhouse gas (GHG) emissions associated with construction and operational material, and energy consumption have been estimated for the Project Design. From these estimates it is evident that materials used (embodied emissions and materials haulage) during construction are expected to be the most significant GHG emission source for the T2D Project.

In calculating the T2D Project’s GHG emissions, an operational period of 50 years was adopted to ensure that ongoing GHG emissions over the whole of life of the project are appropriately accounted for. The main source of operational GHG emissions is anticipated to be generated from traffic flow within the project.

Further details on GHG emissions sources and estimates for the project are summarised below.

Energy usage

A range of energy uses during construction will contribute to the project’s GHG emissions. This includes operating the tunnel boring machines (TBMs) and construction plant, equipment and vehicles used for a range of works, including earthworks and piling and the use of on-site passenger vehicles. It is evident from the calculations, that utilisation of diesel for plant, equipment and vehicles is expected to generate greater GHG emissions than if electricity or cleaner forms of energy generation were used.

The project is also expected to have a significant demand for electricity during its operation. This is largely due to the operational requirements of the project’s tunnels, which include ventilation, lighting, traffic management, communication and safety systems. In addition to the tunnels’ operational energy demands, there will be significant lighting, signalling and safety requirements for surface roads and public realm/pedestrian areas.

Materials usage

The use of concrete is expected to be the most significant source of GHG emissions and environmental impacts during construction.

Photo: Pre-cast concrete tunnel segments

Other significant sources of GHG emissions include steel reinforcement, asphalt and bitumen.

Graphic: Greenhouse gas emissions from materials usage for construction.

For the operations and maintenance phase, GHG emissions are expected to be significantly lower than those generated during construction, typically relating to rehabilitation of pavements, accessible drainage elements such as kerbing and replacement of tunnel mechanical systems.

Circular economy

The project will generate and consume significant volumes of resources during construction, operation and maintenance, including but not limited to spoil from tunnels, cleared vegetation, concrete, asphalt and steel.

As part of the Planning Phase Sustainability Plan, an initial circular economy assessment has been completed to identify opportunities to incorporate reused and/or recycled products/materials into the project and is summarised in the table below. The Contractor will be required to undertake further assessments and nominate targets during the procurement phase. It will be a requirement to achieve or exceed agreed targets during Detailed Design and construction.

Initial circular economy assessment

Photo: Trucks on-site, Darlington Upgrade.

Climate change resilience

A preliminary Climate and Natural Hazard Risk Assessment for the T2D Project has been completed which identified risks and how they can be addressed through adaptation measures - improving the resiliency of the asset. The scope of the risk assessment included the works associated with the design and construction of the project and considered the operational elements of the asset, such as tunnel ventilation, lighting and intelligent transport system (ITS), and maintenance activities. It also considered the interface of the asset with the broader road network and adjacent land uses.

Projections for future climate conditions and changes to natural hazards such as extreme rainfall events were primarily sourced from the Department for Environment and Water’s Guide to Climate Projections for Risk Assessment and Planning in South Australia. The risk assessment summarised the current projections for emissions scenarios Representative Concentration Pathway (RCP) 4.5 (low emissions) and 8.5 (high emissions). The risk assessment has primarily focused on risks in the years 2050 and 2090, as the overall asset design life is 100 years, with several components such as bridge structures and culverts having a specified 100-year design life.

A series of technical workshops were conducted to identify elements to be considered and to subsequently assess potential impacts, the risks they pose and appropriate adaptation measures necessary to reduce these risks.

Twelve priority risks were identified along with adaptation measures that need to be adopted which and are described in the table below.

Overview of priority climate and natural hazard risks and adaptation measures

Climate change risks will continue to be assessed and reviewed throughout the Detailed Design and construction phases of the project.

Greening and water sensitive urban design

Without mitigation, the project would negatively impact vegetation, the existing urban tree canopy and create an increase in impermeable surfaces within the project boundaries. These effects can contribute to an increased urban heat island effect and adversely impact stormwater quality.

The Department has committed to identifying and pursuing feasible opportunities to expand green infrastructure (including water sensitive urban design) on new infrastructure projects through their Green Infrastructure Commitment. Specific targets include:

• a minimum 20% increase in canopy cover is achieved within the T2D Project area, or higher where possible
• a minimum 50% canopy cover is achieved over all pedestrian and cyclist paths, or higher where possible.

An Urban Design Strategy has been developed for the project,  which sets out an overarching urban design vision, principles and objectives that apply project-wide to all works, including the requirement to achieve minimum tree canopy cover targets. These are supported by detailed design requirements for specific locations and project elements, including requirements for green spaces and landscaping in and around the motorway.

Artist's impression: Proposed greening near the Brickworks Marketplace.

During Detailed Design, a Green Infrastructure Assessment including development of a Green Infrastructure Concept Plan and a water quality risk assessment will be undertaken which will identify mitigation measures to reduce urban heat island impacts and improve stormwater quality.

See Landscape and visual amenity and Surface water.

Key sustainability opportunities

The greatest opportunities to reduce GHG emissions (carbon) across any infrastructure project are at the earlier stages of the project. As the detail and accuracy of the project’s design increases, the opportunities decrease and the cost of change increases. As a result, as a project moves through design phases and into Detailed Design, the ability to challenge, influence or alter the design solution reduces and the focus moves towards design optimisation (for example, pavement types or concrete mix designs).

In an effort to provide early design guidance, initiatives which address the key impacts and opportunities were identified early in the planning phase. They were either considered during the Project Design or will be as the design and construction processes progress. Initiatives and opportunities with potential for a high magnitude impact are summarised in the table below.

Key sustainability initiatives/opportunities across impact areas

Key sustainability outcomes already achieved through the Project Design include:

• the use of tunnels across about 60% of the length of the project , reducing surface level impacts on existing trees and vegetation within the corridor
• the proposed ventilation system significantly reduces operational energy demand for the project
• design has aimed to minimise impacts to social infrastructure and community facilities, such as health centres and schools
• use of passive shading elements to provide a natural light transition at tunnel portals
• the motorway design has been slightly re-aligned to the east in the vicinity of to the Brickworks Marketplace, with less impact on community open space/green space at Kings Reserve, and reduced amenity impacts
• revegetation to support enhancement of local ecology and increased canopy cover
• continuity of the shared-use path (SUP) along the length of the corridor, including connections to existing networks, such as the SUP along the River Torrens / Karrawirra Parri linear park and Western Bikeway
• stormwater basins integrated within the landscape design.

Construction

Key initiatives and opportunities identified for further assessment and implementing as delivery progresses include, but are not limited to, the following:

• reduction in whole-of-life GHG emissions and increased recycled content for concrete, pavements, steel reinforcement and noise barriers
• replacing a portion of the construction plant, equipment and/or vehicles which are typically diesel-powered, with electric, hybrid or renewable energy-powered alternatives
• investigation into onsite generation, storage and use of renewable energy
• efficient use of water during construction, including implementing initiatives to reduce water demand, onsite capture and reuse, and use of non-potable water sources.

Operation

Key initiatives and opportunities to be investigated for operations include, but are not limited to, the following:

• tunnel ventilation system design to use much less energy over time
• lighting design optimisation
• onsite generation, storage and use of renewable energy
• efficient use of water during operation of the project, including implementing initiatives to reduce water demand, onsite capture and reuse, and use of non-potable water sources.

Maintenance

Key initiatives and opportunities to be investigated for maintenance include, but are not limited to, the following:

• use of hybrid and electric maintenance vehicles
• beneficial re-use of groundwater from tunnels
• use of recycled materials for pavement resurfacing
• maintaining green infrastructure targets, including increase in 20% tree canopy cover and planting a minimum of 50% local native species.

Approvals, permits and authorisations

A summary of key legislation, policies and guidelines covering sustainability, including an overview of each and their relevance to the project is provided in the table below. Depending on the final sustainability initiatives adopted for implementation as part of the project, approvals, permits or authorisations may be required. For example, if the use of recycled water during construction is implemented, relevant approvals from local councils, SA Water and SA Health may be required.

Key legislation, policies and guidelines

The Project Assessment Report (PAR) community consultation period concluded in April 2024. We thank you for your feedback.

The valuable information and local insights received during the consultation phase of the PAR are being considered by the project team and will inform the ongoing refinement of the T2D Project.