Volvo has developed a self parking car in collaboration with Linköping University

"In the project, four ultrasound sensors have been fitted on a Volvo S60, pointing in the directions indicated in the right figure above. When the driver initiates a parking space scan, the system fires and reads the sensors. A number of clever algorithms turn the measurement data into knowledge about the space position and size. When the space is identified and is determined to be large enough for the car, the system tells the driver that a pocket exists. The driver stops and reverses and the prototype electric power steering as well as braking is controlled by the parking computer so that the car is driven into the pocket safely, as shown in the left movie. In normal usage, though, the driver stays in the car. The human-machine interface can also guide the driver in the case where no electrical power steering exists but with maintained brake control.

Quote from: http://www.ikp.liu.se/evolve/