What is prohibited when traveling downhill with a motor vehicle?

When traveling downhill with a motor vehicle, coasting with the gears or transmission in neutral is prohibited because it significantly reduces the driver's control over the vehicle. When the vehicle is in neutral, the driver cannot effectively apply the necessary power to the engine for braking and maneuvering. This can lead to a dangerous situation, as the vehicle may gain too much speed and the driver will have limited ability to respond to unexpected obstacles or changes in traffic conditions.

Keeping the vehicle in gear while descending a hill provides better traction and braking response, as engine braking can help control speed. This increases safety for both the driver and other road users. Therefore, maintaining control and keeping the transmission engaged is crucial when navigating downhill slopes.