No pedestrians, the sensors only detect plastic bags.

Look, I just don't believe in a no win scenario. Which part of evasive maneuvers don't you understand. :P

This question is answered in the episode "Booby Trap" of STTNG.

"The answer lies in our own computer, the mind, the best piece of engineering we'll ever need. There's no way the computer can compensate for the human factor, the intuition, the experience, the wish to stay alive."