How roadbuilding projects create CO2 emissions and what can be done to reduce them

England’s strategic road network (SRN) – the arterial network of motorways and A-Roads – is the backbone of national prosperity. However, as we look towards a more sustainable future, are we doing enough to ensure our roads meet our need for a low carbon infrastructure?

The second Road Investment Strategy (RIS2) sets out the government’s investment plan for the SRN for the period 2020-2025. The plan outlines £27.4bn of funding for building new road capacity, improving the existing SRN and reducing its negative impacts. It aims to deliver a safer, more reliable and efficient network of roads.

Although the plan prioritises fixing “the strategic roads we have today”, rather than delivering an expansive road widening or building programme, it will nevertheless have a major carbon footprint in its delivery and beyond.

Indeed, the plan is being challenged in court by the Transport Action Network (TAN), which alleges that the government has underestimated the carbon emissions RIS2 will generate.

TAN argues that the plan does not give due consideration to the UK’s climate targets, including reaching net zero on carbon emissions by 2050, and that RIS2 could generate carbon emissions 100 times greater than government estimates.

Given the importance of England’s roads to national prosperity, upgrading and maintaining the SRN is essential. However, ICE has also called for infrastructure planning to be joined up and aligned with wider social, economic and environmental outcomes such as achieving net zero.

How road building generates CO₂ emissions

Road building generates carbon emissions from a variety of direct and indirect sources, including:

• Construction work, such as land preparation, embodied carbon in concrete, asphalt, steel and other raw materials used to build road schemes, and emissions from construction vehicles.
• Tree felling, to make way for roads reducing carbon capture.
• Maintenance and servicing work.
• Roadside and tunnel lighting and signage.
• Increased usage through more vehicles on the road, journeys undertaken and higher traffic speeds.

Evidence suggests road schemes generally induce traffic by enabling more carbon emitting and car-dependent activities and land development, including new manufacturing and freight activities and new houses, business and retail parks. The latter generate carbon emissions during their construction and are often built in locations inaccessible by public transport, thus generating additional car usage.

How can carbon emissions be reduced in road building?

There are a number of measures that can reduce or offset carbon emissions in road building projects. In its RIS2 Delivery Plan, Highways England pledges carbon reduction measures including:

• Using ultra-low emission or electric vehicles where they meet the needs of maintenance and support work.
• Reducing the use of carbon-intensive equipment during road renewal work.
• Incorporating emissions standards into contracts with suppliers.
• Using energy-efficient lighting for roadsides, tunnels and signage.
• Planting trees for capturing carbon near major projects.

RIS2 and the Delivery Plan also incorporate efficiency principles such as lean construction, digital design and off-site manufacturing, which can go some way to reducing environmental impact.

RIS2 also commits to mainstreaming environmental considerations and exploiting “new thinking and technology” wherever possible. There are opportunities for innovation in the design and delivery of road projects, and research is exploring how new materials and technologies could reduce carbon emissions, for example:

• Skanska is trialling graphene-enhanced asphalt in Oxfordshire, which could be more durable than traditional tarmac and therefore require less maintenance.
• In 2019, a stretch of the M25 was resurfaced using 50% recycled asphalt, exploring the potential for more recycled materials to be used in future SRN projects.

Other measures can also have an impact. The long-term switch to electric vehicles by road users will lower carbon emissions. However, it is also necessary to integrate the SRN with active travel and public transport initiatives to encourage use of alternative, low or zero carbon transport options. This should include providing higher frequency and zero emissions bus and coach services across the SRN.

ICE has also advocated introducing a Pay As You Go (PAYG) model for England’s busiest roads. This could reduce congestion, incentivise modal shift and generate sustainable revenue for road maintenance and upgrade.

Alongside maintaining and upgrading England’s vital SRN, the government will need to consider the full range of options for reducing carbon emissions and meeting its net zero target.

More information on how it will approach this will be available when the Department for Transport publishes its Transport Decarbonisation Plan later this spring.