wiki上的功能解釋
This function is meant to indicate a hazard such as a vehicle stopped in or near moving traffic, a disabled vehicle, a vehicle moving substantially slower than the flow of traffic such as a truck climbing a steep grade, or the presence of stopped or slow traffic ahead on a high speed road.
各國在使用時機規定上應該會有小差異
例如歐洲會用於很緊急的煞車
但紐西蘭就不准