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Soil affected roads innovation trial

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Our Soil Affected Roads (SARs) innovation trial page gives details on the project background and aims.

Why is the trial important to Cambridgeshire?

Cambridgeshire is in a challenging position: approximately 40% of our total road network lies on peat-based soils. These roads are prone to seasonal expansion and contraction. This means the roads need more repairs, more often, and this is cost which needs to be covered out of our existing budgets.

What are the aims and objectives of the trial?

Cambridgeshire County Council, in partnership with the Cambridgeshire & Peterborough Combined Authority (CPCA), has launched a £1.5 million trial to address the long-term maintenance challenges posed by soil-affected roads across the region.

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 policy 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.

What are soil affected roads (SARs)?

Soil affected roads (SARs) are parts of the road network that rest on peat or other weak soils. These soils shift with changes in weather and climate. As a result, the roads above them often move, crack, and wear out faster than normal.

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 0%
Extent of soil affected roads Cambridgeshire map
Cambridgeshire map showing extent of soil affected roads

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 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.

Chain Causeway photo showing defects on road surface
B1381 Chain Causeway between Earith and Sutton before reconstruction.

Project 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 CPCA at the Highways and Transport Committee meeting on 4 March 2025.

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.

Map showing trial section of the B1099, Upwell Road, March, Cambridgeshire

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.

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 to stay informed

We will share updates on this website page. Residents, stakeholders, and industry partners can follow the trial and review findings in the case study.

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