Thirteen students and a bus driver were hospitalized Wednesday when a school bus and semitrailer collided head-on.

Officials said the injuries were relatively minor, and three of the children were released to their parents within 90 minutes of the 3:15 p.m. MDT accident in suburban Salt Lake City (search).

"They were lucky," West Jordan Police Capt. Gary Cox said.

It appears the bus driver may have fallen asleep and drifted across the center line, hitting the semitrailer head-on, West Jordan Fire Battalion Chief Marc McElreath said.

Police closed the highway to traffic in both directions, snarling rush hour traffic in Salt Lake's congested southwest suburbs.

The truck driver, a woman from Oregon, was not injured. There were 16 people total on the bus, and the injured were transported by ambulances to three area hospitals.

Four students and the bus driver were at Pioneer Valley Hospital in West Valley City, hospital spokesman Dick Alexander said. Their conditions weren't immediately available.

Five youth aged 12 to 14 were at Jordan Valley Hospital (search) in West Jordan. Nursing supervisor Teresa Brunt said all five were being treated for minor "scrapes and bruises" and were expected to be released.

Alta View Hospital in Sandy got the remaining youth patients, said hospital spokeswoman Jody DeJong who did not know their conditions.

The bus was returning to the Westridge Academy from an afternoon outing when the accident happened at 4610 W. Bingham Road, in West Jordan.

The bus is owned by the private academy, formerly known as the Utah Boys Ranch. A school therapist, Michael Ruoho, said officials were not immediately commenting on the accident.

Officials did not release any names or ages of the victims, or either driver.