Investigators are months away from determining why a university baseball team's bus plunged off a highway overpass, killing seven people, a federal official said Thursday.

An update released by the National Transportation Safety Board said investigators were still reviewing the bus driver's logbook, vehicle maintenance files and the motor coach company's history of operations and safety.

The safety board also wants "to specifically determine the point at which passengers were ejected from the coach and how the fatalities and injuries were sustained," the update said.

The bus carrying theBluffton (Ohio) University team crashed on March 2 after it went up a left-lane exit ramp that dead-ends on a bridge over Interstate 75 in Atlanta. The bus went off the overpass, killing five players, the driver and the driver's wife.

Twenty-eight others were hurt, and one student remains hospitalized.

Investigators previously said the driver apparently mistook the exit ramp for a highway lane, but the safety board's update did not make any finding on the crash's cause.

"There are months of work yet to be done," safety board spokesman Paul Schlamm said.

The update said the investigation team will also review federal and state rules covering the exit ramp and subsequent changes including larger warning signs.

The baseball team was traveling to Florida for a spring tournament.