From Tesla's release notes for its upgraded Autopilot technology based on radar as its primary control sensor:
The net effect of this, combined with the fact that radar sees through most visual obscuration, is that the car should almost always hit the brakes correctly even if a UFO were to land on the freeway in zero visibility conditions.
Taking this one step further, a Tesla will also be able to bounce the radar signal under a vehicle in front - using the radar pulse signature and photon time of flight to distinguish the signal - and still brake even when trailing a car that is opaque to both vision and radar. The car in front might hit the UFO in dense fog, but the Tesla will not.
Of course they're kidding. Or so they'd like us to believe.
Video clip from Close Encounters of the Third Kind (1977).