Air Brakes

The service brakes, the parking brakes, and the emergency brakes.

It applies and releases the brakes when you use the brake pedal during normal driving.

It applies and releases the parking brakes when you use the parking brake control to hold the vehicle in place.

It uses parts of the service and parking brake systems to stop the vehicle if a brake system failure occurs.

So that a backup is available: if the service brakes fail, the parking and emergency systems can still stop the vehicle.