I was initially taken aback by Moscow's gates for the subway but in restrospect they make sense and fit that model. They are (were?) gates that default to open, and stay open if you insert the token/pass. Otherwise they slam shut right in front of you. During rush hour, it's brilliantly simple as the gates just stay open as people pass through. (As a tourist, it was more "interesting" to get the occasional misfire and have it slam right in front of my legs, but that's a different story.)