text: The first reason is sensing the world. Google modified Toytoa Prius uses postioin-estimating senors on the left rear wheel, a rotating sensor, a video mounterd near the rear view mirror, four automotive radar sensors, a GPS reciever, and an intertial motor sensor. These sensors make it much easier to drive by itself. If it can do it by itself then it won't meed the human to do it for it. The most important bit of technology would be the spinning sensor on the roof. It shows you a 3-D model if the vehicles surroundings. The combination of all of these accessories would show how the car could be driverless.