I'm pretty sure I was on the eastbound half of that last night. Well, okay, the next time they say they're having signal problems and proceeding slowly, I might even believe them.
(The reason I'm pretty sure: I'd gotten up to stand in the aisle because I was hoping we'd pull into Back Bay only late-enough that I'd be able to catch the 6:35 bus home -- I'd mostly given up on that at the point we stopped inching along and came to a sudden screeching halt. And then I could see what looked like a train headlight through the front window several cars up and went WTF was that a near miss? And I guess it was.)