You are driving a motor vehicle with a manual gearbox. How do you conserve the service brake when driving down a long downward slope?

You answered correctly. When driving down a long slope with a manual gearbox, you should shift to a lower gear early to use engine braking. This reduces the need to use the service brake constantly, which helps prevent overheating and fading of the brakes. Additionally, using the permanent brake (such as a retarder or an engine brake, if the vehicle is equipped) further conserves the service brake. The parking brake must never be used while driving, as it is only intended to hold the vehicle stationary and could cause loss of control if used while moving. Remember, relying mostly on engine braking and auxiliary brakes on long descents keeps your service brakes effective for when you really need them. This is a key part of safe driving in mountainous or hilly areas in Germany.