Our Soil Affected Roads (SARs) innovation trial page gives details on the project background, aims, and why it is important to Cambridgeshire.
What are soil affected roads (SARs)?
Soil affected roads (SARs) are parts of the road network that rest on peat or other weak soils.
Roads built on peat soil deteriorate faster than roads constructed on other types of soil because peat soil is much more affected by the weather. Wet and dry weather causes peat soil to expand and contract under the road surface.
This continuous movement damages the road, creating cracks, sloping and bumps in the surface. It can also lead to holes opening up in the surface of the road as gaps are created under the road surface.
Why is the trial important to Cambridgeshire?
A large amount of Cambridgeshire including almost all of Fenland is made up of peat soil. Whilst there is peat soil elsewhere in the UK particularly on moorlands, Cambridgeshire is unique in having such a large amount of peat soil in our county, especially underneath our roads. This means over 1800km of our roads are built on peat soils or similar.
The table and the map below show the extent of our soil affected road network.
| District area | Percentage % of road that is soil affected |
| Cambridge City | 0% |
| East Cambridgeshire | 28% |
| Fenland | 93% |
| Huntingdonshire | 15% |
| South Cambridgeshire | 1% |
The extra cost of peat soil affected roads
It costs up to five times as much to repair a peat soil affected road than it does for roads built on other types of soil. This is because instead of renewing the road surface, we have to dig deeper and do more work to reconstruct the road to the same standard.
As a highway authority, this means that we face significant extra costs to build and maintain roads in Cambridgeshire. However, we are funded in the same way as other places which do not have these difficulties.
Trial details
The soil affected roads innovation trial aims to test better, greener, and more cost-effective ways to repair SARs. This will be achieved with a £1.5m funding grant secured from the Cambridgeshire & Peterborough Combined Authority (CPCA) at the Highways and Transport Committee meeting on 4 March 2025.
Aims and objectives
This initiative aims to identify and evaluate the most effective repair solutions for routes impacted by underlying soil conditions.
The trial will provide robust evidence to inform future investment decisions and identify how soil-affected roads can be maintained to a similar standard to non-soil-affected roads.
The findings will support long-term planning, and we hope also to help shape national government policy around fairer funding for maintenance. Ensuring that unique regional challenges to local authorities are recognised, and all communities benefit from safe and reliable transport links.
Trial location
The trial location is the B1099, Upwell Road, March, Cambridgeshire. The section of Upwell Road that meets the B1098, Sixteen Foot Bank, is highlighted on the image below inside the dashed lines.
Approach
We will design a range of innovative treatments. Each treatment will be applied to a specific section of the B1099. Treatments could range from deep soil mixing, chemical stabilisation, deep reconstruction, and lightweight fill alternatives.
Monitoring
We will install monitoring equipment and undertake routine surveys to support a data driven approach to future SAR treatment design.
Trial work to date and next steps
Completed activities
- Soil investigations to help us determine existing road construction and underlying ground conditions.
- Initial design work and preliminary costing based on our soil investigations and the planned trial sections.
Upcoming activities
- Soil testing to inform the design phase.
- Tendering through the Eastern Highways Framework 4.
- Construction of trial sections.
- A 12-month monitoring phase to evaluate performance. The findings will be documented in a case study to guide future approaches to SAR maintenance across the county.
Work stages
Our work is undertaken in stages. The details below outline the approximate duration of each stage.
- Design stage: July 2025 to March 2026
- Pricing stage: April 2026 to June 2026
- Construction stage: July 2026 to September 2026
- Monitoring and case study stage: October 2026 onwards
How we currently deal with SARs
Reactive maintenance
After a road has been identified as being soil affected, we will follow a clear, staged, process to managing the area until repairs can be carried out. This is set out below:
- Make the area safe: we set up temporary warning signs to alert drivers before they reach the damaged section. For example, uneven surface or slow down.
- Routine inspection: a highways officer inspects the route at an increased frequency to make sure everything remains safe and visible.
- Review road safety: we review if extra measures are needed from a road safety perspective. This could include temporarily reducing the speed limit if it makes the area safer.
- Add traffic controls if required: if the road condition worsens, we may use temporary traffic lights to control vehicle flow. In rare cases, we may need to close the road to keep people safe.
Planned maintenance
When we rebuild SARs, we install geogrids to give more stability to the road and limit movement. Since 2016, Cambridgeshire has reused road materials on site. This sustainable method cuts waste, lowers costs, and reduces carbon emissions.
This method works well, but it still needs regular maintenance. It does not solve the long-term problem of weak soil. The trial aims to find durable solutions. Stronger roads will reduce the amount of roadworks, save money, and give residents more reliable journeys.
Use the forward and back arrows on the side of the images below to see the stages of reconstruction of the B1381 Chain Causeway.
2026-27 works on peat soil affected roads
As part of this year’s budget, £2.5m will be spent on repairing peat soil affected roads across the county. This includes £700,000 towards repairing Wells Bridge, Ramsey Mereside.
More information on this year’s planned work, how we prioritise road maintenance and our peat soil affected roads work can be found in our Highways and Transport Committee meeting (3 March 2026) CMIS documents.
How to stay informed
We will share updates on this web page. Residents, stakeholders, and industry partners can follow the trial and review findings in the case study.
