A groundbreaking trial exploring how vegetation removed during highway construction can be transformed into a valuable, carbon-saving material is underway on National Highways' A417 Missing Link project in Gloucestershire.

Led by main contractor Kier and environmental innovation company TerrAffix, the trial is the first of its kind in the UK and involves converting organic waste from the site into biochar, a charcoal-like substance created by burning vegetation at extremely high temperatures in a low-oxygen environment.

The process has already produced five tonnes of biochar on site, equating to a carbon saving of 13 tonnes of CO₂, comparable to the emissions from five flights between London and Perth. Rather than disposing of the removed vegetation, the project turns it into a multifunctional product with several environmental benefits.

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The next phase of the trial will see biochar used directly in the construction and landscaping of the A417 scheme:

• Landscaping: Biochar will be integrated into soil used for planting thousands of trees, helping them establish faster and absorb more carbon from the atmosphere.

• Green Bridge Construction: Biochar will replace synthetic water-retaining gels on the UK's largest green bridge, helping vegetation on the bridge deck survive dry periods by storing and releasing water more effectively.

• Microplastic Removal: The biochar will also be used in the highway drainage system to help filter out microplastics from surface water runoff.

A full case study will be developed at the end of the trial, evaluating the benefits, challenges, and lessons learned. This could pave the way for the wider adoption of biochar across National Highways projects and its broader supply chain as part of efforts to reduce carbon emissions in future infrastructure builds.

The trial is jointly funded by National Highways’ Environmental and Wellbeing Designated Fund and Kier.