The T has started to enforce the surface front door-only policy this past month and it's generating lots of grumbling and confusion. On the "C" line the other day I watched nearly the entire train be forced to line up and disembark at one station, taking many extra minutes. At another station, a man with a large heavy suitcase was blocked by an elderly lady who had already stepped up to the farebox. She had to go back down and get out of the way so he could disembark. He seemed pretty miffed, and even took a picture of the driver with his camera-phone. Elsewhere, I watched a man on crutches be forced to ascend the stairs because the driver wouldn't open the low floor rear doors for him -- even though there was nobody else on the platform at that time, late at night. In general, the operators are taking more care to announce it constantly, "front door-only exit; front door-only exit." But it's often garbled or unclear to many people, who I still see sometimes waiting by the rear door.
At Kenmore station after the baseball game last night, there was a flood of people trying to enter through the array of fare gates. This was well after the game had ended, maybe an hour or so later. The transit police had opened the emergency exit just to allow egress, but they also waved some folks in that way. One woman showed her CharlieCard, I saw, and the officer just waved her through saying, "I believe you." This just goes to show how inefficient even the full-fledged fare gates can be, as anyone who has been caught in such a rush knows.
It's unclear whether there will be any attempt to gather statistics which show that the front door-only policy is cost-effective or beneficial, when compared to the loss suffered through increased round-trip times and missed headways. The Scorecard does not show on-time performance information for the Green Line, and the MBTA does not track Green Line trains on the surface, so they probably do not have that information available. Unfortunately, it seems that this policy is largely driven by political considerations instead of technical merit, and it will probably be politics that ends it as well, as people express their dissatisfaction to the T and to their elected officials.