Traffic on one of the main trunk roads into the Westcountry was gridlocked for more than two hours on one of the busiest days of the year this weekend.
Police were called to the A30 between Lifton and Launceston just after 1.30pm on Saturday after a car overturned on the westbound carriageway.
Inspector Andrew Hamilton, of Devon and Cornwall Police, said one person was reported trapped in the vehicle and fire brigade, ambulance and Cornwall air ambulance were also scrambled.
The day is acknowledged by police as being one of the busiest of the year on the road as holidaymakers flood west.
Insp Hamilton said the incident did cause some headaches.
"We had to close the road because of the nature of the accident, but we were able to divert most drivers off the A30 at Lifton and around to Launceston.
"We also notified drivers via the network signs on the M5 that the A30 was closed.
"This would allow people who knew the area or could make arrangements to take an alternative route.
"However there were some delays while the incident was attended to."
It is not yet clear how the car came to be on its roof and Insp Hamilton said the matter was being investigated.
The 58-year-old driver did not receive major injuries, although he was trapped in the vehicle for about 20 minutes.
Insp Hamilton said: "The male driver was trapped but he had not suffered serious injuries.
"He had cuts to his arm and the road was closed to assist with getting him out of his vehicle safely.
"He was released by the fire brigade and taken to Derriford Hospital in Plymouth by land ambulance on a spinal board as a precaution."
One lane of the A30 was reopened just before 2.30pm and the road was entirely cleared within the hour.