This is the 643rd most frequent Korean word.
사고를
"사고를" means "accident" or "thought" (as the object form, depending on context).
In this sentence, '사고를' refers to an 'accident,' specifically a traffic-related one, in the context of an event being witnessed.
그는 교통 사고를 목격했습니다.
He witnessed a traffic accident.
Here, '사고를' is used to indicate 'accidents' in general within the context of taking preventative actions.
사고를 방지하기 위해 안전 조치를 취해야 합니다.
Precautionary measures must be taken to prevent accidents.
In this sentence, '사고를' refers to a specific accident that led to the implementation of regulations.