California Motor Vehicle Code 21457
The Meaning of Flashing Signals
California Vehicle Code 21457 explains the indication of flashing red or yellow lights in traffic signals. A flashing red stop signal that flashes intermittently means that the driver facing the signal must approach the intersection, stop completely before entering the crosswalk or the intersection, and then proceed through the intersection under the same rules as stopping at a stop sign.
A traffic signal that usually guides vehicles with green, red, and yellow lights, may occasionally show a flashing red signal. This usually means that something has gone wrong with the light system, and that all vehicles entering the intersection must do so as if it was a four-way stop. Proceeding with caution is especially important when an intersection has signals which are out of the ordinary, as approaching drivers will expect the usual traffic lights.
A flashing yellow light is shown, it means the driver is allowed to pass through the intersection or turn with caution. Like a regular yellow signal, "caution" is key. Flashing yellow left-turn signals indicate that vehicles wishing to turn can enter the intersection in the left-turn space, but must wait for through-traffic to pass through the intersection.
A good way to approach flashing lights is to do so with extra attentions. Remembering the rules of stop signs at flashing red lights and watch out for road hazards or special regulations in effect when encountering flashing yellow lights.