What is the right thing to do in this situation?

In this situation, the correct action is to perform an emergency braking manoeuvre. This is required whenever there is an immediate danger that requires you to stop as quickly as possible to avoid a collision or prevent danger to others. German traffic rules state that emergency braking is necessary in unexpected situations, such as when a red traffic light appears suddenly or if an obstacle or hazard arises that makes continued driving unsafe. Being ready to brake is important, but if there's a clear and immediate reason to stop—like a red light or sudden obstruction—emergency braking is the safest and correct response according to the German road traffic regulations. Selecting this answer shows an understanding of the need to react quickly and decisively when the situation demands it.