It is pretty straightforward if the light turns green to yellow, STOP (if it’s safe to do so). Legally, every driver has to stop at a yellow light unless he or she is too close to the intersection to stop safely before entering the intersection. Failing to do this means you might find yourself in the middle of an intersection where crossing traffic has a green light, the right of way, and you’ve not only run a yellow light but a red light!

A flashing yellow light means something else.  A flashing yellow means you should proceed with caution, knowing cross-traffic may be entering.  Flashing yellows exist at many busy intersections, and during construction or after a power outage, a traffic light might not be functioning correctly. As a safety measure, the intersection runs a default program. The busier of the two intersection streets gets a yellow flashing light, while the less busy intersection gets a flashing red light. The flashing red light means: Come to a complete stop as if you’ve stopped at a stop sign and proceed only when clear. The flashing yellow light means: "proceed with caution." Traffic facing the yellow light has the right-of-way, but oncoming traffic usually also has a flashing yellow light, and cross-traffic will have a flashing red light.