A driver has suffered serious injuries in a collision on the A428 near Eltisley.
Cambridgeshire police were called shortly before 7.30am to reports of a two-car crash near the A428's junction with the B1040.
The collision involved a blue Peugeot 207 and a black Volkswagen.
The East of England Ambulance Service was also called to the scene.
A spokesman for the East of England Ambulance Service said: "A rapid response vehicle and ambulance crew were dispatched and treated a man in his 50s for centralised neck pains.
"He was conscious and breathing but needed cutting free from the vehicle with the assistance of the fire service. After that, he was conveyed to Hinchingbrooke Hospital for further treatment."
The road was blocked for more than two hours, causing delays eastbound to St Neots and westbound to Caxton Gibbet, before finally being re-opened shortly after 9.30am.