What signifies that a vehicle can legally proceed at an intersection?

Answer: A — solid green traffic signal

A solid green traffic signal signifies that a vehicle can legally proceed at an intersection. When the traffic signal is green, it indicates that the traffic flow is clear and vehicles may move through the intersection, provided it is safe to do so. Drivers should still be attentive to other vehicles and pedestrians that may be crossing or approaching the intersection. The green light governs right-of-way and ensures that vehicles can advance when conditions permit. In contrast, a flashing yellow light typically warns drivers to proceed with caution, indicating that they should be alert and yield to any oncoming traffic or pedestrians if necessary. It does not grant the same authority to proceed as the solid green light does. A stop sign requires drivers to come to a complete stop and yield to any traffic or pedestrians before proceeding. A yield sign instructs drivers to slow down and yield the right-of-way to any vehicles on the intersecting road, meaning they should only proceed if it is safe to do so. Thus, the solid green traffic signal most clearly indicates that a vehicle can legally and safely move forward at an intersection.