The A14 spur road near Alconbury was closed for almost two hours following a “multi-vehicle collision” this morning (Monday).
Emergency services were called to a stretch of the road between junction 14 with the A1(M) and junction 23 at the Spittals interchange at about 7.30am.
The East of England Ambulance Service and Cambridgeshire Fire and Rescue Service joined Cambridgeshire police at the scene. The collision is understood to have involved five vehicles.
A diversion on the A1(M) south to Brampton Hut and the A14 eastbound to junction 23 was put in place while emergency services worked to clear the scene.
A spokesman for the Bedfordshire, Cambridgeshire, and Hertfordshire road policing unit said one lane was re-opened at about 9am, with both lanes re-opened by 10am.
A rapid response vehicle from Magpas also attended the scene, with a man treated for serious injuries to his leg.
A spokesman said: "The Magpas enhanced medical team assessed the patient, in his 20s, who had sustained a serious leg injury. They worked alongside Cambridgeshire Fire and Rescue Service to safely extricate the man from the vehicle and sedated him at the scene.
"The doctor-paramedic team then accompanied the patient to Addenbrooke's Hospital via land ambulance where he was in a stable condition upon arrival."