If you ever go to the Frankfurt Airport, don't get too alarmed the first time you see someone trying to push a luggage cart onto the escalator. You see, unlike most regular carts, these ones have been designed to grip onto the edge of the step, locking the wheels in place. You can even use them on a down escalator. Just make sure that your bags aren't piled too high, as that same German design team is still working on a system to bypass the laws of gravity.