The posted speed limit is 65 mph for cars and 55 mph for trucks and buses. Police have not said how fast the bus was traveling or if driver fatigue was an issue.
The agency's order, signed by regional field administrator William Paden, states that an unannounced investigation began a few days after the crash and found "a management philosophy indifferent to motor carrier safety." It said the company does not monitor its drivers' hours of service or require them to submit records of duty status.
Other problems include neglecting to properly maintain driver-qualification requirements and vehicle-maintenance records, as well as a failure to require drivers to prepare driver-inspection reports.
"The ongoing compliance review and investigation has discovered a deterioration in your safety management controls and widespread safety violations that demonstrate a continuing and flagrant general disregard for compliance," the document states.