Climate grassland retrofit
This project aims to reduce soft estate maintenance by trialling low-nutrient substrates such as crushed chalk that slow vegetation growth and improve safety and biodiversity.
These low nutrient systems significantly slow vegetation growth, reducing annual maintenance visits while improving biodiversity, lowering carbon emissions, and enhancing safety. A trial retrofit will be designed in 2025/26 and delivered in 2026/27, targeting one or more high maintenance sites identified by Operations in the Southeast region. The work builds on successful small scale retrofits at A27 Patcham and the A35 Monkey Jump Roundabout.
National Highways is facing significant operating expenditure constraints in Road Period 3 (2026-31), leading to a significant reduction in proposed soft estate maintenance budgets. Certain areas of soft estate, such as sight lines, require multiple maintenance visits per year for safety reasons, with grassland cut up to 8 times a year.
These areas have significant maintenance burden, and maintenance activities mean road workers have to be on the network under traffic management multiple times per year. The project designed replacing the vegetation and soil in one of these high maintenance areas with low nutrient substrate to reduce vegetation growth, reducing maintenance visits, saving money and increasing safety.
Objectives
Enhance worker safety by reducing the need for repeated visits under traffic management.
Reduce the frequency of maintenance visits at high maintenance grassland sightlines.
Lower operational carbon emissions associated with repeated grass cutting activities.
Improve roadside biodiversity through establishment of species rich, low nutrient wildflower grasslands.
Test and validate a retrofit approach that can be scaled nationally.
Success criteria
Reduced need for road workers to be on the network under traffic management, increasing safety.
Significant reduction in maintenance frequency (from 8 cuts to 1–3 per year, or potentially lower).
Quantifiable OpEx savings at the trial site(s), with a projected payback period of 1–3 years for a £180k investment.
Reduction in operational carbon proportional to reduced maintenance activity.
Increased biodiversity following establishment of wildflower rich grasslands.
Evidence to support development of a national delivery model or specification for future retrofits.
How the project supports National Highways KPIs
Safety (KSIs) improves because fewer maintenance visits mean road workers spend less time on the network under traffic management, and improved visibility enhances driver sight lines, reducing the likelihood of incidents.
Network availability improves because reduced vegetation growth lowers the need for maintenance closures.
Efficiency improves because cutting high maintenance areas fewer times each year reduces total maintenance costs.
Carbon emissions reduce because less maintenance activity means less operational carbon from grass cutting.
Biodiversity improves because enhancing small areas of grassland supports nature’s recovery and contributes to National Highways’ biodiversity outcome of achieving no net loss.
The approach
The project will design at least one low nutrient retrofit in the 2025/26 period, focusing on a high maintenance Soft Estate sightline. The retrofit process involves removing existing vegetation and 20–30 cm of nutrient rich topsoil, replacing it with a low nutrient medium such as chalk, and seeding with appropriate wildflower mixes. This method reduces grass dominance and limits growth rates, cutting requirements and supports long term biodiversity.
Operations Southeast (Ops SE) identified seven “crossover cuts” as potential sites. These collectively cost £1.39m–£1.49m annually to maintain at current cutting frequencies.
Project obstacles
During feasibility, the project identified several issues that would need to be managed ahead of delivery. These included cost variability across the seven potential retrofit sites, the requirement to remove varying levels topsoil across different sites before installing low nutrient materials, potential for utilities and contaminated materials, and the coordination needed with Ops SE during soil removal and material import.
How they were addressed
Cost variability, mitigated through Ops SE identifying seven crossover cut sites to support comparison and inform selection of one or more retrofit locations.
Topsoil removal requirements, addressed by drawing on learning from previous retrofits such as A27 Patcham and A35 Monkey Jump, which informed planning for topsoil removal and installation of low nutrient substrate
Operational coordination, solved through early engagement with Ops SE, including feasibility approval on 7 April 2025, which supported planning for delivery, soil removal and material logistics.
Potential presence of utilities and contaminated land, managed through appropriate ground investigation during the feasibility stage.
Outcomes and impact
The project has proven the potential to deliver these predicted results.
- Potential enhanced safety, with fewer road worker visits under traffic management.
- Potential maintenance reduction, from eight cuts per year to three or fewer, with some comparable sites requiring no maintenance for four years.
- Potential annual savings, of approximately £932k across seven sites, or £66k–£212k per individual site.
- Potential material reductions in operational carbon, due to fewer maintenance interventions.
- Potential biodiversity uplift, as wildflowers thrive in low-nutrient conditions.
- Potential creation of a habitat that is more ecologically resilience, as ground conditions will favour stress tolerant plants.
User and stakeholder outcomes
Regional engineering teams, Service Delivery staff and Soft Estate managers are expected to benefit from reduced maintenance pressure, enabling resources to be redirected to other priority tasks. Road users are expected to experience fewer closures and less traffic management as maintenance frequency decreases, supporting local economic activity.
Stakeholder engagement is already strong, with the South East Operations Directorate, Head of P&D, and Regional Head of Service Delivery bought into the approach.
Key insights and learning
Previous small ad hoc trials highlighted the potential of low nutrient retrofits to reduce maintenance, improve safety and deliver wider environmental benefits. The process also showed the value of applying learning from previous retrofits and working closely with Operations to align planning, site selection and delivery to scale benefits. Investigation of high maintenance locations and the initial innovation investment created operational momentum and unlocked further funding for additional schemes.
Key insights include:
- Low nutrient substrates have the potential to significantly reduce grass growth while enhancing biodiversity.
- Retrofitting offers a cost-effective alternative to repeated annual maintenance interventions, with quick return on investment.
- Early retrofits elsewhere on the network provided valuable learning and demonstrated multi year maintenance reductions.
- Targeting high maintenance sites maximises savings and accelerates payback.
- Cross regional coordination is essential for planning and safe delivery.
- The initial innovation investment generated strong operational uptake, with the approach incorporated into an existing safety scheme and funding secured for further schemes.
- Strong opportunity for scaling, with operational funding enabling wider rollout to realise predicted benefits and wider network gains proven through the initial innovation investment.
Future value and next steps
The approach is now positioned to progress through operational funding, with capital and budgets enabling multiple schemes to move forward next year. This creates a clear opportunity to expand delivery and embed low nutrient retrofits within wider maintenance and safety programmes.
Next steps include:
- Deliver of pilot projects and measure benefits.
- If successful, developing a national retrofit specification for low nutrient grassland treatments.
- Scaling delivery to additional high maintenance sightlines, supported by operational funding.
- Reducing operational carbon emissions through fewer maintenance interventions.
- Enhancing biodiversity across the Soft Estate as wildflower rich grasslands establish.
- Integrating the retrofit approach into routine asset management and future RIS programmes.
