When backing up a vehicle, what must be operational?

When backing up a vehicle, the operational requirement of the backup alarm is crucial for safety. The backup alarm is designed to alert pedestrians and other vehicles in the vicinity that the vehicle is reversing. This is particularly important in areas where visibility may be limited, ensuring that those around the vehicle are aware of its movements and can take appropriate actions to avoid accidents.

In contrast, while it is important for brakes, headlights, and wipers to function correctly for overall vehicle safety, they do not serve the specific purpose of signaling when a vehicle is in reverse. The backup alarm is uniquely intended for this function, making it essential for safe backing procedures.