Adding fare gates to just some stations of a pay-the-conductor system seems to generate a whole new set of behaviors and a certain amount of disagreement about who is cheating whom, who is benefitting unfairly, and so on. Two quite different methods of payment with two quite different sets of assumptions about when in the travel process you actually pay coexist rather awkwardly. It is a lot like the doors on the Boeings. This is just about what the comments at the beginning of the thread say. This was predictable; many of you predicted it.
Tap-on, tap-off POP with a unified fare structure for all modes and roving inspectors charging 10x the fare as a fine seems like it would be simpler, more effective, faster, and less morally uncertain all around. Oslo does this, but has one car per train -- clearly marked -- where you can board without a ticket and pay. Any other car, you get fined if caught without. Of course, that requires all-door boarding and plenty of space in all cars... Utah Frontrunner has a ticket machine on every platform; they have a lot fewer platforms and a lot more trains per day per platform, so that spreads out the cost.
Nothing new in my post, so here's this memory from about 1989:
Christmas Eve, or maybe Dec. 23, Needham Heights train: the conductor handed back all the paper tickets unpunched. Policy? Just him? Right? Wrong? I don't know. I do remember that I never got around to using the ticket before it expired -- I rarely rode the commuter rail and just happened to be on it that day.
Merry Christmas, everyone, and a happy new year of continued civil (mostly), intelligent (nearly always) discussion.