Remember what "skitching" was when you were a kid? It involved getting behind a car, usually in the winter, and hanging on to the rear bumper while it drove along using the ice to help you glide (unless you can run a lot faster than most people :) ).
Right here in the high rent district of River North I saw two guys in rollerblades "skitching" on the tail of a Ford Mustang as it drove south on Wells street. It was crazy! The car must have been going 30 miles / hour and there was a cab right on their tail, probably ready to run them down if they had lost their grip (there is no way the cab could have gotten out of the way). I can't believe I saw that, too bad I didn't have my camera for that shot.
As far as danger it reminds me of driving in a cab in New York City in the tunnels under the various rivers. There is no shoulder down there and the cabs drive right along side the walls of the tunnel as they whip to the airport. There are many "blind" curves where you can't see if someone's car has broken down so you would just crash into them full speed and cause some kind of crazy chain reaction. I used to work for a guy who swore that one time he was in a cab next to another cab that slammed right into a car that was changing a tire and some horrible wreck ensued, but his cab of course just kept on moving. Can't be verified, but quite a believable story from my perspective.