The eastbound stretch of the A45 was closed between Great Billing and Earls Barton yesterday (July 16) after a collision involving a van and a lorry.
All emergency services - including the air ambulance - were called to the A45 eastbound just before the Earls Barton turn off just before 11.40am.
The westbound carriageway was temporarily closed for the air ambulance to land.
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A spokeswoman for Northamptonshire Police today said: "The man was taken to University Hospital Coventry & Warwickshire where he remains.
"We don’t believe the injuries are life threatening or life changing at this time."
Northamptonshire Police and Highways officers spent the last few hours turning vehicles around caught in the tailbacks, which was completed at around 3pm.
A spokeswoman for Magpas Air Ambulance said: "At 12:17pm yesterday afternoon Magpas doctor Scott Knapp and paramedic Steve Chambers landed on the A45 in Northampton via the Magpas Air Ambulance. They had been called to treat a man who had been injured in a collision between a van and a lorry.
"The Magpas enhanced medical team assessed the patient, who was in his 50’s, and had sustained multiple serious injuries. They provided him with care at the scene before airlifting him to University Hospital Coventry and Warwickshire. The man was in a stable condition upon arrival."