Final answer:
When a driver extends their left arm out and upward, it means they are indicating a left turn.
Step-by-step explanation:
When a driver extends their left arm out and upward, it means that they are indicating a left turn. This hand signal is commonly used when the vehicle's turn signals are not functioning properly or when the driver wants to make their intentions clear to other drivers on the road.
For example, if a driver wants to turn left at an intersection, they can extend their left arm out the window and angle it upward, demonstrating their intention to turn left.