The most common meaning; refers to the red-yellow-green lights controlling road traffic.
The traffic light at the next intersection turned red.
信号機が故障しているので、警察官が交通整理をしている。
Because the traffic signal is broken, a police officer is directing traffic.
signal device; semaphore
Broader meaning: any mechanical or electrical signaling apparatus, such as railway signals or industrial indicators. Less common than sense 1.
鉄道の信号機は、列車の安全を守る重要な装置だ。
Railway signals are important devices that ensure train safety.
The traffic light changed from red to green.
Cyclists also have to obey the traffic lights.
The traffic light malfunctioned due to the typhoon, causing chaos at the intersection.