A man in his 40s was seriously injured after hitting a guardrail and going off the road in Salaberry-de-Valleyfield Thursday afternoon.
The vehicle overturned and he ended up on the roof.
The driver, who was alone in the car, had to be taken to hospital.
At first, his condition was deemed critical but by the evening he appeared to be doing better, according to the Sûreté du Québec.
The police launched an investigation to determine what happened.
The accident could have been caused by inattention, fatigue or discomfort , according to Sergeant Audrey-Anne Bilodeau, spokesperson for the SQ, adding that drunk driving and excessive speed had already been dismissed.