Modern air brake systems combine three different systems. They are the service brake, parking brakes, and the?

• A. Anti-lock brakes
• B. Emergency brakes
• C. Hydraulic brakes
• D. Vacuum brakes

Answer: (B)

In modern air brake systems, three braking subsystems work together: the service brakes for normal stopping controll by the driver, the parking brakes to hold the vehicle when it’s parked, and the emergency brakes as a safety backup that can stop the vehicle if the air supply fails. The emergency brakes kick in automatically when air pressure drops to a low level or if there’s a significant system failure, providing a fail-safe stop so you can still bring the vehicle to a halt.

Other options don’t fit this trio. Anti-lock brakes are about preventing wheel lock during braking, not a separate system in the air brake setup. Hydraulic brakes rely on fluid pressure, and vacuum brakes are an older, non-air system—neither aligns with the three-part air brake configuration.