It is most useful for seeing sharp contrasts, such as the painted white line of a crosswalk on a dark road.

WSJ: The Quest to Create A Bionic Eye Gets Clearer

Using a series of sensors, cameras and servos the car is able to turn the steering wheel plus activate the throttle and the shifter to navigate across this stretch of road, relying on the road markings painted on the floor to both keep it driving in a straight line and to have it stop, respectfully, at the crosswalk.

ENGADGET: Nissan NSC-2015 self-driving car with LTE and smartphone connectivity (test-ride with video)