You should learn the difference between a single sensor return and a full perception result. Also, look up sensor noise, integration time, classifier inputs and training. Please tell me how you're planning on dealing with rain and snow.
Yes, if it was as simple as a magic sensor that could tell you instantly at max range 1) that the thing is a car (even though you won't see all of it immediately) 2) what its velocity vector is and 3) what its going to do, then yes, things are as simple as you wish they were.
But they are really, really not.