Which of the following is NOT recommended when descending steep hills?

• A. Downshift before cresting the hill
• B. Use the trailer hand valve as needed on steep hills
• C. Pump brakes to maintain air pressure
• D. Maintain a steady speed and downshift

Answer: (B)

When driving a combination vehicle down a steep grade, you want braking to be predictable and balanced between the tractor and trailer. Using the trailer hand valve engages the trailer brakes independently, which can cause the trailer to brake harder than the tractor. That can push the rear of the tractor, reduce steering control, and even lead to a jackknife or loss of control on a long downgrade. The safer approach is to rely on engine braking by downshifting before the crest and to apply the service brakes smoothly to maintain a controlled, steady speed. In practice, downshifting before the hill and keeping a steady speed with controlled braking are the recommended techniques, while using the trailer hand valve for descent is avoided because it can destabilize the vehicle.