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Reducing carbon on UK’s road schemes: actions to take for the sake of climate change

July 06, 2021

By Jon Heath and Simon Earl

As civil engineers, we have the responsibility to make sure our built environment supports the climate change and social value agenda

We have a responsibility as civil engineers to wave the environmental flag, and the duty to question standard practices, find other solutions, and try something new.

By looking at alternatives to the norm, a Wiltshire-based development is attempting to cut their embodied carbon on a road scheme in Chippenham. It’s time to have the same discussions across regional and local authorities to drive change in support of climate targets. 

Road schemes are usually contentious; if we do nothing, we run the risk of increased traffic congestion, and higher air pollution rates. Where we do something, we must consider all low carbon options from the beginning. 

Managing a carbon hotspot

Because it’s not possible to eliminate carbon in an infrastructure project, the emphasis should be on managing it using the PAS 2080 process (Carbon Management in Infrastructure). On a road scheme generally, the asphalt across the layers of a road pavement design is likely to be a carbon hotspot if traditional techniques are used. Hot rolled asphalt is a commonly specified material, which involves a mixture of aggregate, bitumen and other additives heated up at a mixing plant and delivered to site at temperatures between 120 and 140 degrees Celsius before laying and rolling it into place. 

On a road scheme, the asphalt across the layers of a road pavement design is likely to be a carbon hotspot.

At the design stage of the Chippenham development, Stantec’s carbon review process identified the potential to use warm mix asphalt (WMA) in pavement layers. WMA, mixed and delivered at lower temperatures, can reduce the embodied carbon of asphalt by around 15%. We found that the local highway authority (as the adopting authority of the road scheme) was open to using WMA and is considering updating its local specifications accordingly. They can clearly see the benefit that this innovation can provide to aid their own Climate Emergency declaration and their drive to net zero carbon. But we can and should encourage a faster uptake across all Local Highway Authorities; after all, climate emergency commitments need to drive our national infrastructure agenda now. 

Collaborate to drive down carbon

WMA is just one of the solutions we can commonly adopt across our schemes, from private developments to major national programmes for new infrastructure and road improvements. For years, asphalt producers have been using recycled aggregate in their mixing process and there are other innovative recycling ideas to consider, for example: Tarmac is trialling the use of rubber granules from old tyres in asphalt mixes. One of the main principles of PAS 2080 is close collaboration with materials suppliers and we must encourage this as a fundamental part of the design process to drive down carbon.

Reducing carbon in our infrastructure is in the spotlight and the Government mandate to reach net zero by 2050 means Local Authorities need to adopt innovative measures.

As designers, we need to think carefully about the thicknesses of asphalt materials. Another PAS 2080 principle is to reduce the quantity of materials used. Specifying permeable asphalt may well save carbon in new materials and installation for the road drainage system. Where we need to refurbish a road, we can incorporate reinforcement grids through stress absorbing membrane interlayers (SAMI). This approach would help us to re-use existing base layers. Like WMA, these are not necessarily new concepts, but we must give them credit as being an important part of reaching Local Authority climate change commitments.

At the design stage, Stantec’s carbon review process identifies the potential to use warm mix asphalt in pavement layers.

Specifying the use of WMA in Wiltshire proved that thinking outside the box can successfully reduce the carbon footprint of road schemes. Since then, we at Stantec are in detailed discussions with multiple Local Highway Authorities and the private sector about associated carbon benefits. Schemes range in scale and complexity from relatively minor highway schemes to a 10km road enhancement. This is the next stage for us, to encourage change across the whole spectrum of national road programmes. To a certain extent, it’s a behavioural change, with Local Authorities needing to alter their requirements and scheme details—from using materials they know and love, to being open to other technically viable suggestions.

From an engineering sense, we can’t find a reason why we shouldn’t roll out this process, literally, on our nation’s roads. Reducing carbon in our infrastructure is in the spotlight and the Government mandate to reach net zero by 2050 means Local Authorities need to adopt innovative measures. As engineers of our existing and future infrastructure, we have a moral obligation to support them, especially as we issue our own sustainability targets and statements!

Changing the conversation

The challenge isn’t harder than it looks—we’ve made changes fairly easily by changing the emphasis of the design conversation to be more carbon focussed. The PAS 2080 process for managing carbon encourages the whole supply chain to work together across a scheme. We need true collaboration to make it easier still; everyone doing something to reduce carbon is far more effective than a few people doing carbon management perfectly.

It’s become our nature as civil engineers to be efficient in design stages and reuse as much possible, so we’d expect that many of our engineering solutions will naturally bring about a carbon reduction. We must reinforce this and re-double our efforts to collaborate with our associated professionals and the asset owners. The coming years are widely accepted as our last chance to begin a reversal of the climate emergency, and we have to do this together.

As designers, we need to take the supply chain with us and show Local Authorities how the materials and new technology work, and importantly how we can help with their climate commitments. The PAS 2080 mantra of reduce, reuse, recycle ought to be considered across all projects, and it’s our responsibility to challenge when we see an opportunity to be better. There is no doubt that reversing climate change is a huge challenge. With clients, local authorities, designers, materials suppliers and contractors working together, we can drive out low carbon solutions for the good of the planet.

  • Jon Heath

    Leading a team of engineers and technicians on civil engineering and infrastructure design, Jon is a civil engineer with over 20 years of experience on earthworks, utilities, drainage, and flood risk management.

    Contact Jon
  • Simon Earl

    A chartered civil engineer and multi-disciplinary project manager, Simon has delivered projects in the residential, commercial, health, and education sectors as well as led highways and transportation frameworks.

    Contact Simon
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