The above person is correct. As I work at the FIRST Summer Camps, we have a segway demo every week and most of the questions you are all asking are really common, and there is an answer for all of em. It is a very safe and reliable type of transportation. If u get off it, it will go forward for about 10 seconds, then gives a handle shake (the handle shakes, if u couldn't guess), and then shuts itself down. If it does hit a person, it pushes the handle bars back just like u would if you where on it and thus stopping it. Also, you could put your hand or foot on the ground and get it run over by the Segway and it wouldn't even hurt, I learned that first hand (no punn intended).
Hope that helps
-Matt