What should be used primarily for slowing down when driving downhill?

Using both engine and auxiliary brakes is the best approach for slowing down when driving downhill. Engine braking occurs naturally when the driver takes their foot off the accelerator, allowing the engine to slow the vehicle as it works against the power from the wheels. This type of braking helps maintain better control and reduces wear on the regular braking system.

Auxiliary brakes, which are additional braking systems often incorporated into larger vehicles, provide an extra measure of control, enhancing the overall braking performance. These systems can include features like exhaust brakes or compression release brakes that further assist in slowing down the vehicle without solely relying on hydraulic braking forces.

By utilizing both engine and auxiliary brakes together, drivers can manage their speed effectively while minimizing the risk of brake fade, which can occur if regular brakes are overused on long downhill stretches. This approach ensures the vehicle remains stable and under control throughout the descent, making it a safe choice for handling steep declines.