[patrick451]

When a Tesla can accelerate to 60 mph in less than 2 seconds, knowing the instantaneous velocity and acceleration is not very meaningful. You really need to be able to predict what the acceleration profile will look like over the next N seconds of your maneuver. Holding the currently perceived velocity and acceleration constant over the next N seconds is one naive way to do that. But the actual set of possible trajectories of the other actor is much larger, and you need to drive more conservatively to account for that.