Access to Witney: A40 slip road improvement scheme

Client: Oxfordshire County Council

Duration: February 2025- ongoing

Access to the A40 from the east of Witney was limited to eastbound on-slip and westbound off-slip resulting in all westbound traffic having to travel through the centre of the town, causing congestion and reduced air quality.

To improve connectivity, M Group Highways has delivered the construction of a new eastbound off-slip and westbound on-slip, along with infrastructure upgrades, on behalf of Oxfordshire County Council.

Our team began work in February 2025, beginning enabling works to prepare the site for the main construction phase, which started in May 2025.

Our M Group Highways civils projects team has worked to deliver a complex infrastructure scheme that:

• Improves road connectivity to and from Witney via the A40.
• Minimises disruption to live traffic during the project.
• Meets strict deadlines for utility diversions and critical works.
• Provides value engineering opportunities through Early Contractor Involvement (ECI) and construction to assist client with budget constraints.
• Overcomes environmental and logistical challenges, including protected species and deep excavations.

Between February and April this year, our team completed the enabling works. In this phase, we:

• Constructed a site compound and car park.
• Installed site perimeter fencing.
• Cleared trees and vegetation.
• Created access for the main works by constructing the slip road bell-mouths.
• Excavated deep utility trenches and completed trenchless digging beneath the live A40 to divert over 250m of overhead services overground.
• Temporarily widened the B4022 to maintain traffic and pedestrian flow during works.

The enabling works allowed our team to begin the main works in May. Currently ongoing, this phase will see us excavate and remove over 50,000m³ soil from the A40 embankments and create two new slip roads, including new drainage systems with three attenuation ponds. We’ll also upgrade signalised junctions, electrical ducting, cabling and street lighting.

During the main works, we will also realign and resurface the B4022, including building a new footway and install deep drainage.

Throughout the project our team worked with client and stakeholders to overcome challenges including:

• Utility Diversions: We coordinated with SSE to meet tight deadlines for underground cable installation before an overhead shutdown (requiring a 12-week lead time).  We also adjusted the diversion location by 30m due to a live badger sett, avoiding ecological impact.
• Horizontal Directional Drilling: Drilled an 80m section, 4m beneath the live A40, successfully pulling through five ducts while monitoring carriageway settlement. Completed in under two weeks.
• Budget Constraints: Successfully implemented multiple value engineering solutions, aligning with scheme objectives and achieving significant cost savings.
• Bulk Earthworks Efficiency: Leveraged machine control technology on dozers and excavators, completing the phase in 3 months. Achieved a record day of 341 lorry loads removed thanks to favourable weather and efficient quarry turnaround. We also reused nearly 4,000m3 of excavated subsoil and 3,000 tonnes of topsoil.

Despite the challenges, our team completed enabling works on time, allowing the main construction to start without delays. Utility diversions were completed in line with SSE’s planned shutdown, avoiding extra costs and keeping power supplies running. Bulk earthworks were carried out ahead of schedule, showing strong efficiency and good use of resources.

By working closely with the client, we found ways to deliver value engineering, even within strict technical requirements. Environmental standards were met throughout, including the careful handling of the badger sett and other local wildlife considerations.

The project is on track to ease traffic in and out of Witney, cut congestion, and support economic growth in West Oxfordshire. Once complete, it will provide a safer and more reliable transport link for the local community and businesses.