A new federal report says a passing car that went out of control caused an Alabama school bus wreck that killed four students in 2006.
The wreck led to new rules for school bus safety.
The National Transportation Safety Board report released Thursday also says the bus driver was not wearing a seat belt and was ejected from the bus when it hit an overpass wall after the car hit it.
With no one at the wheel to hit the brakes, the bus plunged from the overpass and nose-dived 300 feet to the pavement below.
The crash led the National Highway Traffic Safety Administration to mandate design changes for certain buses to protect children on them.