Reducing carbon for greener roads ahead

Roads are sometimes seen as antithetical to decarbonisation, standing in the way of active transport and densification, but they are also economic and social lifelines.

Australia | 21 February 2024

Roads are a means by which we transport essential goods, visit our relatives, and increasingly facilitate the passage of green transport such as zero emission vehicles and active, shared or public transport options.

Undeniably, constructing and maintaining roads is carbon-intensive and energy-hungry, calling for large quantities of materials to be mined, manufactured, transported and placed. But can anything be done about this? Is it possible to create a ‘green road’?

Frameworks for carbon measurement and sustainability in road projects

The need for a more sustainable approach to road projects is increasingly being integrated into policy and legislation, embedded into business cases, and expected by communities as a component of social and environmental licence. Transport for New South Wales (TfNSW) recently announcing a Net Zero and Climate Change Policy which legislates targets for operational and embodied emissions.

The challenge of accurately measuring and actioning these commitments is sizeable, and will require learnings from both local and global examples. The National Highways Net Zero Carbon Plan in the UK, for which WSP was lead advisor is a good place to start. TfNSW is partnering with National Highways to share best practice and accelerate progress.

“The simple reality is that there is no net zero Australia without net zero roads. Transport agencies are all facing the same challenges in a safety critical industry. So it makes every sense to collaborate, share learnings and work together to make faster progress together” says David Symons, Director, Sustainability and Climate Change, WSP in the UK.

For transport agencies and planners to make informed decisions in balancing infrastructure needs with reducing carbon emissions, calculating a project’s carbon footprint early and valuing carbon appropriately are integral to success. WSP has recently been supporting Austroads on the Transport Agency Emission Reduction Opportunities project, developing Decarbonisation Decision Making Guidance incorporating assessment of whole of life carbon and cost-effectiveness, among other criteria.

PAS2080, the carbon management standard for buildings and infrastructure is an emerging international standard for carbon management in infrastructure and buildings. WSP worked with UK National Highways to achieve accreditation for PAS2080 in 2023 and some government agencies in Australia are beginning to also mandate this, along with Infrastructure Sustainability ratings which have seen growing adoption in recent years.

WSP has also developed the Carbon Zero framework, which our UK team is using to assist clients to make informed decisions considering the whole of life carbon impacts in early transport planning and strategic options assessments.

Consider carbon emissions at a transport system level

Before road projects are planned, leaders must ask whether they are necessary at all or indeed whether construction will support, or harm net zero progress. Alternatives to new infrastructure such as adjustments to traffic flow, tolls, mode shift or intelligent transport systems, public transport or active travel approaches could meet the need. This goes to the heart of PAS2080 which right from the start challenges roads authorities to think at the whole transport system level. And to question whether a new road or rail is genuinely the best way to meet a transport need.

If new infrastructure is required, the approach should consider how to make new assets more resilient and Future Ready^TM, minimising the need to build more later. Applying a circular economy approach to road design and construction A circular economy is based on the principles of designing out waste and pollution, keeping products and materials in use and regenerating natural systems. This approach holds promise for delivering more sustainable road projects, as it can reduce the carbon-intensive task of creating and transporting new materials but the approach requires consideration at every stage.

The 10 R's of a circular economy approach

Designing infrastructure for longevity, adaptability and materials optimisation, and selecting products with a high potential for reuse or recycling can improve sustainability outcomes. Establishing a materials database can inform reuse and end of life decisions.

Valentina Petrone, WSP’s Circular Economy lead in Australia, says “Applying a circular economy approach is critical for clients to achieve net zero targets, but perceived extra costs can remain a pressing factor in their decision-making.

“To address this, we are exploring ways to quantify and measure the benefits of reusing materials including avoiding disposal costs and reducing energy and water consumption by not using virgin materials,” she says. “It remains a global challenge to find the right metrics to demonstrate the business case, risk and opportunities – but this is a key part of our work to promote greater circularity."

WSP has been working with our clients to embed a circular economy approach on road projects such as the M12 Motorway in Western Sydney, and for precincts such as the Moree Plains Shire Council Special Activation Precinct in regional NSW. We’ve also collaborated with the NSW Office of Energy and Climate Change to develop circular design guidelines for the built environment.

Low-carbon asphalt and alternative materials

The available options for low-carbon materials generally achieve equivalent, or improved performance compared with conventional materials, but have a reduced carbon output. They can incorporate demolition waste, crushed glass, fly ash, plastics and crumb rubber to name a few. Selecting suitable sustainable road materials involves a complex analysis of factors including cartage, energy usage, durability and reusability but, when it is done right, the results can be impressive.

WSP has been working with Fulton Hogan in Brisbane to explore the use of recycled asphalt, as well as asphalt mixtures that enable the thickness of the asphalt layer to be reduced, and mixtures that incorporate less hydrated lime, which deliver energy savings due to the lower temperature required for manufacturing.

WSP’s Senior Principal Consultant and highly experienced asset manager Mark Faulkner says that these innovations are achieving “As much as 40% emissions reduction in the materials, coupled with energy efficiency benefits and reduced waste – all delivered to the client at a similar cost.”

Elsewhere, UK National Highways’ approach has focussed on providing long term signals on the carbon intensity of products it will purchase – giving the market confidence to invest. Its carbon in procurement policy is also looking to monetise carbon in the tender process – investing in strong data systems to capture forecast and actual carbon emissions accurately.

Designing and building more efficiently with digital twins and modern methods of construction

A digital-first approach can increase certainty and address concerns about cost, measurement or the effectiveness and timeliness of adopting new sustainable methods or materials. Here are some examples of how:

Digital twins can make designs and construction processes more efficient, and deliver a better understanding of the carbon footprint of the design. Design optimisation as part of this process can reduce the volume of materials required and lead to carbon and cost savings.
Digitally enabled design can make it easier to apply modern construction methods including modular or standardised components, which can be fabricated offsite to high safety and quality standards and be reused across multiple projects. This is often a less carbon intensive means of production.
Digital tools make it easier to calculate, map and track emissions, even automating carbon estimation into digital design tools. WSP’s CAESAR tool maps cartage, which can inform material choices to reduce the emissions resulting from transporting those materials.

Resilience and longevity in changing times

In addition to sustainability imperatives, the road sector faces considerable change over coming years. As zero emission vehicles (ZEVs) become more prevalent, road infrastructure must provide the necessary charging facilities to support them and to consider how this is likely to impact road managers and industry practice.

WSP is currently working with Austroads to consider how this is likely to impact road managers and industry practice. With increasingly volatile weather predicted due to climate change, designing for climate resilience will also be crucial to maximising the ongoing performance of road infrastructure and reducing the need for repairs, lessening the impacts on affected communities, and how renewable energy can be incorporated. ZEVs present another challenge due to their heavier weight.

As a large contributor to transport emissions, the role of roads in decreasing them cannot be ignored. While zero emission vehicles will improve tailpipe emissions, a comprehensive view of the design, construction and reuse of roads is needed to approach the net zero targets that are set. There are many levers we can pull to spur on incremental improvements and new technologies are developed every year. While it is a technical challenge, the biggest shift will come from a change in mindset and a willingness to approach things differently.