His speeding and lack of preparedness to drive the bus physically caused the crash. He swerved onto the shoulder, hit the guardrail, and hit two sign posts that damaged the bus and injured and killed passengers. “But for” his negligent speeding and tiredness, the crash would not have happened. In terms of proximate cause, he should have known that 78mph in a 50mph zone while exhausted would foreseeability result in a crash that injures his passengers.