Aerial pictures show Black Cat roundabout progress
Aerial footage showed part of a £1bn project to build a new 10-mile (16km) dual carriageway, which National Highways said was "on track".
Some 80,000 drivers a day use the Black Cat roundabout in Bedfordshire, where the A1 converges with the A421 and A428.
The new carriageway will link it to the Caxton Gibbet roundabout in Cambridgeshire, and half of the cost of the upgrade is going on this junction and its new three-tier gyratory system.
Senior project manager for National Highways, Paul Salmon, said it was the "most complex and most challenging" part of the four-year project but they were "absolutely where we need to be, we're on track".
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