Investigators found no mechanical problems with the Greyhound bus that crashed in Northern California, killing two passengers.
California Highway Patrol Officer Chris Miceli says the investigation continues into the cause of Tuesday morning's accident on a rain-soaked San Jose freeway.
Eight other passengers and the driver were injured when the bus plowed into safety barrels and flipped on its side, coming to rest on the median divider. All are expected to survive.
Investigators earlier ruled out drugs or alcohol as a cause.
Miceli says the driver told investigators he was tired and had bought a cup of coffee at a stop about 30 miles before the accident.