Go with Caution

Flashing yellow phase of San Francisco traffic signal Double-yellow caution phase of San Francisco traffic signal

Scattered about San Francisco are traffic signals in which the green light has been replaced by a yellow light. In the signal phase for traffic to proceed, the yellow light flashes (left). In the caution phase (right), the yellow light is steady and the center yellow light is on as well. This is most common at intersections where traffic can't go straight ahead, but must turn either left or right. That's the case for northbound traffic on Spear Street at Harrison Street.

There are similar signals where the caution phase only has the center light on (there are a few of these in Oakland as well).