Modern air brake systems combine three different systems. Which are they?

• A. Service brakes, Parking brakes, Emergency brakes
• B. Service brakes, Hydraulic brakes, Emergency brakes
• C. Parking brakes, Emergency brakes, Speed brakes
• D. Service brakes, Parking brakes, ABS

Answer: (A)

Air brake systems on heavy vehicles are built from three braking subsystems: service brakes, parking brakes, and emergency brakes. The service brakes are what you use during normal driving—the pedal sends air pressure to apply the brakes on all wheels to slow or stop the vehicle. The parking brakes are designed to hold the vehicle in place when you’re parked; they’re typically spring-applied and air-released, giving a strong hold when parked and releasing when you supply air pressure. The emergency brakes act as a backup to the service brakes, engaging to help stop the vehicle if there’s a loss of air pressure or other service-brake failure, providing a fail-safe option. ABS, while an important safety feature that helps prevent wheel lock, is not counted as one of the three primary brake systems in this context.