WFMZ-TV reports that the ruling came from the Lehigh County coroner on Tuesday, who ruled Smith's death an accident.
Officials with the Parkland School District in Lehigh County had said the bus driver, 42-year-old Kelly Smith, may have experienced some sort of medical problem just before or during the accident, but the coroner said the autopsy revealed no evidence of that.
District officials said Smith, 42, a driver with Parkland for a dozen years, had just dropped off students at the high school and was on her way to pick up kindergarten students when her bus struck a car on Schantz Road in Upper Macungie Township, Lehigh County and then crashed into the township building.
There were no other serious injuries in the crash, but the township building did suffer significant damage.
There were no students on the bus at the time.
Sam Ashmar, a township supervisor and fire marshal for Upper Macungie's Station 56, told WFMZ-TV on Tuesday that the damage is still being assessed, but early estimates are between $200,000 and $300,000. Ashmar's office was heavily damaged in the crash.
Ashmar said a portable office is being brought in for use by the township and Pa. Sen. Pat Browne, who has a district office in the building, while repairs are made.