Which flashing mode shows circular yellow indications to major street approaches?

The correct answer is the yellow-red flashing mode. This mode is specifically designed to provide a warning to drivers approaching an intersection on the major street, indicating that they should reduce speed and prepare to stop.

In this mode, the circular yellow indications alert the drivers of the major street that they do not have a green light and must be cautious as they approach the intersection. The flashing yellow light signals that the intersection is potentially dangerous and that drivers should yield to any conflicting traffic or pedestrians. This setup is particularly useful at intersections where a minor street may be entering the major street, allowing for safe merging and reducing collision risks.

The other flashing modes do not adequately convey the same caution for major street approaches. For example, the red-red flashing mode typically applies when all traffic at the signal must stop, which wouldn’t provide the necessary caution for vehicles on a major street. The yellow-yellow and green-red modes also serve different purposes and do not utilize the same visual cues to indicate caution and readiness to stop for major street traffic.