Other forms: red lights
The red light in a traffic signal tells drivers to stop. When it changes from a red light to a green light, drivers can go.
Most traffic signals have three lights, a red light at the top, green at the bottom, and a yellow or amber light in the middle that means "slow down." If you're driving and see a flashing red light, it acts like a stop sign — you have to stop completely before proceeding. Red lights in general signal some kind of warning, and they're used everywhere from railroad lines to subways and river locks.