From the radar's point of view going uphill, the road disappeared. The radar would see a horizon, and empty air in front of the car, like the edge of a cliff.

From the radar's point of view going uphill, the road disappeared. The radar would see a horizon, and empty air in front of the car, like the edge of a cliff. From its point going downhill it would look like an angled metal wall, or a bump, or something, and then the horizon and empty air beyond it.