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

When driving down a long slope with a manual gearbox, you should "drop down the gears in plenty of time" and "use the permanent brake" (service brake) appropriately to control your speed safely. Shifting to a lower gear uses engine braking to slow the vehicle, reducing the need to continuously apply the service brake. The service brake should be used in a controlled and intermittent way (not constantly) to avoid overheating and losing braking power. The parking brake is not suitable for this situation because it is meant to hold a stationary vehicle and not for speed control during driving. Using engine braking combined with controlled service braking helps maintain a safe speed and preserves the effectiveness of your brakes on long descents.