Final answer:
You should use a low gear to slow your vehicle down when going downhill, when going uphill, when approaching a stop sign, and when driving at high speeds.
Step-by-step explanation:
When you need to slow down your vehicle, you should use a low gear when going downhill. This is because a low gear provides more resistance, which helps in slowing down the vehicle. It also prevents excessive use of brakes, which can lead to overheating and brake fade.
Using a low gear when going uphill can help maintain control and prevent the vehicle from rolling backwards. When approaching a stop sign, it is ideal to gradually slow down and shift to a low gear to match the lower speed and prevent abrupt stops. Finally, when driving at high speeds, using a low gear can help control the speed by increasing the engine's resistance, providing better control and reducing the need for excessive braking.