What must a driver do before making a left turn at a green light?

Before making a left turn at a green light, the driver must yield to oncoming traffic and wait for a safe gap. This is crucial because oncoming vehicles may be traveling straight through the intersection and could pose a risk during the turn. Yielding ensures that the driver assesses the speed and distance of approaching vehicles, allowing for a safe maneuver.

Additionally, while signaling the turn is important for communication with other road users, it's not sufficient on its own to ensure safety. Checking the rearview mirror is valuable for monitoring the environment around the vehicle, but does not address the critical factor of oncoming traffic. Ensuring no pedestrians are crossing is also vital, but yielding to oncoming traffic takes precedence when the light is green and a turn is planned. Thus, the necessary action is to yield to oncoming traffic while looking for a safe gap before proceeding with the turn.