WASHINGTON, D.C. — The severity of injuries in a 2008 school bus rollover was mitigated by the use of lap belts, according to federal investigators.

In a report on the May 2008 crash near Milton, Fla., the National Transportation Safety Board (NTSB) said that no one was ejected from the bus as it rolled, and only two people were seriously injured. Fourteen passengers sustained minor injuries.

The Okaloosa County School District bus was transporting 14 third-graders and three adults on a field trip when the bus driver drifted partially into the left lane of a highway. An SUV that was passing in the left lane struck the bus, which moved back to the right and then overcorrected to the left into a grassy median, where it rolled at least twice. The body of the bus separated from the chassis.

NTSB found that the probable cause of the crash was “the school bus driver’s failure, for undetermined reasons, to maintain her traffic lane, which resulted in the bus being struck from behind when it drifted into the left lane and into the path of an oncoming faster-moving vehicle.”

NTSB said that its investigators travelled to the accident site “to examine the effectiveness of seat belts in school bus rollover accidents.”

Since 2001, Florida has required new school buses to be equipped with seat belts, and the law requires students to wear them.

The bus driver in the Milton crash told investigators that she and an adult chaperone confirmed that the students were wearing their lap belts prior to departure.

In its report, NTSB compared the outcome of the Milton crash to that of a comparable school bus rollover in Flagstaff, Ariz., in 1996.

In the Flagstaff accident, the bus driver also overcorrected to the left, and the bus rolled 1 ¼ times in a median strip. The bus was not equipped with passenger restraints, and five passengers were ejected. One of those ejected suffered a severe head injury requiring long-term care, and another sustained a cervical spine injury resulting in quadriplegia.

In the Milton accident, NTSB noted, “only one passenger (who may have slipped out of a loosely worn belt) and the driver sustained serious injuries, and these injuries are unlikely to require long-term care. No passengers were ejected from the bus during the Milton overturn sequence.”

For the full NTSB report, click here.