What is the purpose of the parking brakes when parked on a downgrade?

The primary purpose of parking brakes, often referred to as emergency brakes, is to prevent the vehicle from rolling when it is parked, especially on a downgrade. When parked on an inclined surface, the weight of the vehicle can cause it to roll down due to gravity. Engaging the parking brake creates a mechanical grip that holds the vehicle stationary, ensuring safety and stability in those conditions.

While properly parking the car is important, that encompasses more than just the function of the parking brake. Proper parking involves turning off the engine, placing the transmission in the correct gear (or 'park' mode for automatic vehicles), and engaging the parking brake to secure the vehicle. The significance of the parking brake is centered on its role in immobilizing the car.

Signaling other drivers does not pertain to the function of parking brakes, which are not designed for communication on the road. Their specific function is to provide security for the parked vehicle against unintentional movement. Hence, the correct answer emphasizes the importance of preventing rolling when parked on a slope.