The obvious question is safety. Google is addressing this as best they can thus far, and will continue to do so in testing. The cars have sensors that remove blind spots and can spot objects as far away as two football fields in any direction. One other design feature: the prototype cars cannot go over 25 miles per hour. While that's great for safety, it means you won't be taking a road trip in a Google car. These are more for going to the store for now.
As for the design, Google kept it very simple. Unlike previous attempts to modify existing cars, Google built this one from the ground up. They look a bit like a Fiat met a character from the Disney movie Cars. The cars have two seats inside, seat belts, a small space for belongings, a start button, a stop button and a screen to show the route. It's also completely electric.
Google is building about a hundred prototypes and launching full blown testing this summer. The test models will still have manual controls (in case the cars get too autonomous and rebel.) If the tests go well, Google will launch a pilot program in California over the next few years.