The scene is familiar to anyone who has navigated a supermarket parking lot: A man gets into his car to leave, and an absentminded shopper abandons a cart behind him. The driver begins backing up. There's no crunch. In this DaimlerChrysler video, the car stops an inch from the cart even though the driver never applied the brakes.An onboard computer did it for him, with help from a radar system mounted on the bumper. Carmakers are working on systems that send out pulses to determine the location, size and distance of objects and then reflect that information back to sensors on the front and rear bumpers, according to the Associated Press.