Final answer:
The hand signal where a driver's hand and arm are extended downward indicates an intention to slow down or stop the vehicle. This signal is an important part of road safety communication between drivers.
Step-by-step explanation:
The meaning of a hand signal when a driver's hand and arm is downward is to indicate that the driver intends to slow or stop. In the context of driving and road safety, this hand signal is crucial for communicating with other drivers, especially when vehicle lights are not functioning or in conditions where they may not be visible. It is important to remember that different hand signals can convey various actions, and understanding them can enhance road safety.