LAX - in the days before TAP it was possible, albeit tricky, to park at the aviation green line station, go upstairs and wait for a train, and then to come down when one arrives so as to blend with the crowd. the airport shuttle driver would occasionally ask to see your metro ticket, but they only checked to see if you have one - they didn't check the date or time on it. i don't know this still works with the pretend turnstiles.