Quote Originally Posted by gerbick
I saw a bike once go down the street by itself...
Sorry to ruin your memory about that but it is possible to do that. You just take the bike, hold it by the grip on the handle bar and the bike seat and then start running. Then when you can't run any faster you give it a shove. The bike will go for a bit before falling over once it loses momentum. This may have been what you saw but if it didn't fall over...