£1 Billion A428 Upgrade Hits Major Milestone as Halfway Point Reached

The UK’s largest ongoing road construction project — costing up to £1 million per day during its peak — has officially reached its halfway stage, according to National Highways.

The ambitious scheme involves building a brand-new 10-mile dual carriageway between the Black Cat roundabout near Roxton in Bedfordshire and the Caxton Gibbet roundabout near Cambourne in Cambridgeshire. Once completed, the route will significantly improve travel times between Milton Keynes and Cambridge, while also easing congestion at one of the region’s most notorious bottlenecks.

Designed to support smoother journeys to major east coast ports such as Felixstowe and Harwich, the project is expected to transform one of the UK’s most problematic stretches of road. The current single carriageway A428 has long been a source of delays and safety concerns, especially around the Black Cat junction — which handles nearly 80,000 vehicles daily.

“The Black Cat has been known for years as a hotspot for congestion and collisions,” said a project representative. “This development removes those issues and unlocks traffic flow for the entire corridor.”

Key Infrastructure Upgrades

Black Cat Roundabout OverhaulA major redesign will see the creation of a modern three-tier junction connecting the A1, A421, and surrounding roads. A1 traffic will run through a newly built underpass, while A421 traffic will travel over the junction via a flyover. Local roads, such as Bedford Road, will remain at ground level to support seamless local connections.

River Great Ouse ViaductA 240-metre viaduct is being constructed to span the River Great Ouse between Roxton and Little Barford, enabling uninterrupted traffic flow across the river.

Railway Bridge Over East Coast Main LineA newly designed bridge will carry traffic safely over the East Coast Main Line, one of the UK’s busiest railway corridors connecting London and Edinburgh.

St Neots JunctionEast of St Neots, a new junction at Cambridge Road will include two ground-level roundabouts connected by a bridge over the dual carriageway, which runs in a cutting below. This improvement will offer enhanced access to the town and train station, making local and regional travel quicker and safer.

Caxton Gibbet JunctionIn Cambridgeshire, the Caxton Gibbet roundabout is being transformed into a split-level junction. A new flyover will carry dual carriageway traffic over the existing A428 and A1198 junction, while local traffic will continue to use the roads at ground level.

Looking Ahead

Construction on the £1 billion scheme began in December 2023 and is on track for completion by spring 2027. The project employs around 850 workers across the site and offices. Earthworks peaked during the summer months, marking one of the busiest periods in the project timeline.

Paul Salmon, Senior Project Manager at National Highways, praised the progress: “Reaching the halfway mark on schedule and within budget is a huge achievement for the team. It brings us one step closer to delivering a safer, faster, and more reliable route for everyone who uses it.”