Commercial Driver License (CDL) Class B Practice Test

When braking a tractor-trailer with ABS, how should you apply the brakes?

1. With maximum force

2. Gradually to avoid skidding

3. Only use the necessary braking force to stop safely

4. Rely solely on the engine brake

The correct answer is: Only use the necessary braking force to stop safely

When braking a tractor-trailer equipped with Anti-lock Braking System (ABS), the recommended approach is to use only the necessary braking force to stop safely. This method allows the ABS to function effectively, as it is designed to prevent wheel lockup during hard brake applications. By applying the brakes with the appropriate force, you maintain better control of the vehicle while still allowing the ABS to engage and modulate braking pressure, ensuring that the wheels continue to rotate and provide traction. Using maximum force can lead to wheel lockup, which contradicts the purpose of ABS—to maintain steering control while braking. Gradually applying brakes could work in certain situations but is not the most effective method for maximizing the advantages of ABS, which is designed to handle sudden and hard braking scenarios. Relying solely on the engine brake would not engage the service brakes properly during such situations, potentially leading to an unsafe stopping condition. Therefore, the correct approach maximizes safety and control while utilizing the features of the ABS effectively.