DUNNIGAN, Calif. — A Greyhound bus that originated in Seattle rolled onto its side today, seriously injuring four and disrupting holiday traffic on the state's major north-south corridor. The bus carried 39 passengers.

The four were taken to a hospital with injuries ranging from moderate to major, Highway Patrol Lt. Joe Whiteford said. It was not clear whether the bus driver was among the injured. Greyhound officials said 14 other passengers were treated and released at area hospitals. Officials could not say whether any of the injured were from Seattle.

The bus was traveling from Redding to Sacramento on Interstate 5 when it ran off the road about 40 miles north of Sacramento. Highway patrol officials were investigating whether it was trying to avoid a car that had swerved in front of it.

The southbound lanes were closed to make room for helicopters and ambulances, but officials reopened at least one lane later in the morning.