I know the T too well for my own good.
Waiting for a train home from Copley today, the day before the marathon, I saw a single Type 8 car pass by bound for Government Center. For a moment I couldn’t imagine why they’d run a single-car train on any line today. Then, an instant later, I figured it out: they’re supplementing service to the underground stations independent of the branch lines. They must be looping at Government Center and reversing in the siding after Blandford Street.
As soon as I’d finished working through this line of reasoning, the T conveniently validated my entire theory; another individual Type 8 car passed on its return trip. Destination: “B – Kenmore.”
(On the other hand, I did choose to take the D Branch immediately after a Red Sox game got out this afternoon, so I guess I’m still a few credits away from a Master’s in Boston transportation. They taught that on day one. Literally. )