On a long, steep downgrade, the use of brakes is primarily a supplement to what?

The correct response highlights the importance of engine braking as a fundamental mechanism in managing vehicle speed during a long, steep downgrade. Engine braking occurs when a driver releases the accelerator, causing the engine's resistance to slow down the vehicle. This method utilizes the engine's compression to assist in deceleration, which is critical for maintaining control and preventing the brakes from overheating.

While brakes are essential for stopping and controlling speed, relying solely on them during a steep descent can lead to brake fade, where the braking capacity diminishes due to overheating. Therefore, engine braking acts as a primary method for controlling speed, with brakes serving as a backup or supplement to this process. Utilizing both methods effectively allows for better management of vehicle dynamics, especially in challenging driving situations like steep downgrades.