Ontario Provincial Police say Highway 400 is open again after it was shut down in both directions south of Barrie because an accident about midday Saturday.

Police say a wheel flew off of a southbound SUV and struck the windshield of a vehicle heading north, seriously injuring the driver.

Emergency crews airlifted the driver, a man in his 20s, to Sunnybrook Hospital in serious but not life-threatening condition. His condition has since improved, and police say he is stable.

A woman in her 20s in the car was treated for minor injuries and shock.

The southbound lanes of Highway 400 at Highway 89 were shutdown to allow for the airlift, while the northbound lanes were closed for several hours on the busy long weekend.

Police say they have impounded the SUV and its wheel as part of their investigation.