What is the rule regarding operating a motor vehicle in neutral while traveling downhill?

Operating a motor vehicle in neutral while traveling downhill is unsafe and is prohibited. When a vehicle is in neutral, the driver loses the ability to control the car's speed effectively. This lack of control can lead to dangerous situations such as increased momentum and difficulty in steering.

When driving downhill, it is essential to maintain control, and shifting into neutral removes the engine's ability to assist with braking through engine braking. This is important for safety, as it maximizes the driver's ability to respond to sudden obstacles or changes in terrain. The prohibition ensures that drivers remain fully engaged in operating their vehicle, particularly in challenging driving conditions like downhill slopes.

The other options suggest varying degrees of permissiveness and caution, which do not align with the established safety rules regarding vehicle operation and control.