The team leading proposals to upgrade the A428 between the Black Cat Roundabout and Caxton Gibbet have started work on a series of ground investigations.
Starting on Monday, almost 400 individual investigations at sites in Bedfordshire and Cambridgeshire will give engineers a clear picture of the type of soils, rock and groundwater along the entire 10-mile route of proposed new dual carriageway.
The work will include drilling almost 100 boreholes, ground water sampling and monitoring, more than 200 shallow trial pits and a wide range of geophysical surveys.
The ground investigations - which will run for about six months - will provide information that will be vital in the design and construction of the new road. Highways England A428 Black Cat to Caxton Gibbet scheme programme lead Lee Galloway said: "The A428 Black Cat to Caxton Gibbet scheme will help transform one of the most congested sections of roads in the region. The complex programme of tests and surveys we're undertaking will help us to better understand the ground conditions, allowing us to build safely, in a way that protects the environment.
"This preliminary work will enable us to get the clearest possible picture of what will be involved in building the new 10-mile stretch of dual carriageway. This is valuable for when we apply for planning consent next year and will help ensure our construction programme can get the new road open in 2025/26."
The investigations will be carried out along the entire route of the proposed dual carriageway. As much of work will take place on private property, such as farm land and industrial sites, there will be minimal disruption to drivers, Highways England stressed. However, there will be some lane closures on the A1 north of the Black Cat roundabout - currently scheduled for three weeks from October 17.
The A428 scheme would see a new 10-mile dual carriageway linking the Black Cat roundabout in Bedfordshire to the Caxton Gibbet roundabout in Cambridgeshire.
The project would replace the only remaining section of single carriageway between Milton Keynes and Cambridge, tackling one of the region's most notorious congestion hotspots.
Highways England ran an eight-week consultation on the proposals between June 3 and July 28, with about 2,500 people taking the chance to discuss the proposal at one of 15 consultation events.
To find out more about the proposals, visit: www.highwaysengland.co.uk/a428.