Paramedics were called to the first southbound Tring junction, near the Crows Nest, at 7.25am.
They found a silver Peugeot 307 in the ditch with two people inside.
Paramedics assessed one patient at the scene for neck pain before taking them to Stoke Mandeville Hospital.
It is believed the other person did not require any treatment.
The incident was dealt with by 9am and traffic is now flowing freely.