Which system does the hand brake complement in a vehicle?

The hand brake, also known as the emergency brake or parking brake, is designed specifically to complement the braking system in a vehicle. Its primary function is to provide a mechanism for securing the vehicle when parked, preventing it from rolling away, especially on an incline.

When the primary braking system is engaged through pressing the brake pedal, the hand brake serves as an additional backup. It operates independently from the hydraulic brake system found in most vehicles, typically using a cable system that directly engages the rear brakes. This redundancy is vital for ensuring safety; in the event of a failure in the main brake system, the hand brake can help to stop or hold the vehicle in a stationary position.

The other systems listed, such as the cooling system, transmission system, and suspension system, play different roles within the vehicle's operation and do not directly relate to the function of the hand brake. Therefore, recognizing the hand brake's role in the vehicle’s braking system is important for understanding its function and the overall safety mechanisms in place.