Which brake system applies and releases the brakes when the driver uses the brake pedal?

The service brake system is designed to be the primary method of slowing down or stopping the vehicle when the driver applies the brake pedal. This system operates through the vehicle's brake components, engaging the brakes at each wheel as needed. When the driver presses the brake pedal, hydraulic fluid is sent through the brake lines to activate the brake calipers or wheel cylinders, applying the brakes.

The emergency brake system, in contrast, serves as a backup and operates independently of the service brakes, typically engaging to prevent the vehicle from rolling when parked or in emergencies. The pneumatic brake system utilizes compressed air to apply the brakes and is commonly found in larger vehicles like trucks and buses, but the driver primarily interacts with the service brake system. Hydraulic systems, while they can be part of the service brake mechanism, specifically refer to the fluid used for transferring braking force, but do not define the overall function of engaging and releasing brakes upon pedal activation.