Your hands don't even need to be touching the steering wheel for it to start spinning back and forth aggressively, all by itself - slowly guiding the car into the parking spot. Parallel parking is designed to be a breeze with the Intelligent Parking Assist system, part of a new $2,200 option package for Toyota's Prius gas-electric hybrid in Japan. This is a bold and somewhat unnerving concept, a car that parks itself. As a driver, you've got to wonder as the Prius eases back toward the curb: What is this machine thinking? If you know Japan, it should come as no surprise that about 80 percent of its Prius buyers have opted for Intelligent Parking Assist. This is a country of famously narrow streets and cramped lots where squeezing into spaces can be a blood pressure-raising exercise. Parking Assist relies on a built-in computer, steering sensor, a tiny camera in the car's rear and a dashboard display shows the image taken by the camera. When you near a parking space and shift into reverse, computerized lines pop up on the display, along with arrows pointing up, down, left and right. Using the arrows, you move the lines around until they define exactly where you want the car to be parked. Then you push the "set" button on the display. Keep your foot lightly on the brake pedal, and the car will start backing up, the steering wheel responding to an invisible hand. Voila, the car will park itself in the spot you've chosen with the arrows. Word.