Final answer:
Under normal conditions, in order to engage the parking brakes, the driver must be sure that the air brake system is fully pressurized. This ensures the proper functioning of the hydraulic system that engages the brakes.
Step-by-step explanation:
Under normal conditions, in order to engage the parking brakes, the driver must be sure that the air brake system is fully pressurized. This is because parking brakes in cars use a hydraulic system known as Pascal's principle to engage the brakes. When the driver pushes the brake pedal, the force is increased by the simple lever and hydraulic system, which applies the same pressure to the wheel cylinders, creating the force needed to engage the parking brakes.
When the air brake system is fully pressurized, it ensures that the brake pedal can effectively transmit the force to the wheel cylinders, allowing the parking brakes to engage properly. Therefore, before engaging the parking brakes, the driver must be sure that the air brake system is fully pressurized under normal conditions. (brakes)