Complex sentence: Bui Baby happens to be a regular passenger during the occurrence of the accident and sees the driver of the private car acting unusual and also the bus driver falling asleep at the wheel.
Split into simpler sentences: Bui Baby happens to be a regular passenger on the same bus driver vehicle during one of these extreme shifts and witnessed the occurrence of an accident. She sees the driver of the private car acting unusual and also the bus driver falling asleep at the wheel.