In the United States, there are no national traffic guidelines, but the sequence for traffic lights is usually red, green, yellow and back to red, although some are simply red-green-red.

"Yellow" means halt at the stop line. Drivers may only proceed when the yellow light appears if stopping is likely to cause an accident.

At night or in the early hours of the morning, some junctions and crossroads have flashing traffic lights. A flashing red light indicates "stop" (as at a four-way stop) and a flashing yellow light means "yield" - that is to say, drivers are allowed to proceed if it is safe to do so.