Which action occurs when the parking brake control is activated?

When the parking brake control is activated, the parking brakes are applied. This is a crucial safety feature in vehicles equipped with air brakes, serving to secure the vehicle when it is stationary. The parking brake operates independently from the service brakes, which are used when driving.

When the parking brake is engaged, it applies a force to the brake components that prevents the wheels from moving. This is essential in preventing the vehicle from rolling when parked, particularly on inclines or declines.

The other options do not correctly describe the function of the parking brake. The service brakes engage differently; releasing air from the tanks is not associated with activating the parking brake; and the emergency brakes function independently of the parking brake system. Thus, focusing on the purpose of the parking brake highlights its role in vehicle safety and stability when stationary.