While Google's prototype self-driving car does a fine job commanding headlines, automakers have been rolling out the features that will ultimately lead to a road-ready autonomous vehicle. Cadillac Super Cruise is an important step in that process. Like current adaptive cruise-control systems, Super Cruise, which GM will likely debut by 2016, controls the throttle and brakes and adjusts the distance between the car and surrounding traffic. But Super Cruise adds another detail: It steers. A processor combines camera, radar, and GPS data to guide the car down the center of its lane.