Check out http://www.robopark.com. These folks seem to have come up with an idea to stack cars next to each other using robots. It aims to accomodate more cars (trust me, their claims are pretty interesting in terms of saving space) using robotic ‘parkers’!! A similar concept is used by Volkswagon at one of their German facilities where they have their entire fleet on displacy. Its a neat concept and hopefully we will get to see it in action in the near future.