What the frickinfrack happen to the Grey Dog on the left, that the roof became mostly separated from the body?!? I'm hoping no one was decapitated....
I'd say the rivets busticated. I was going to say maybe the emergency personnel sliced the top open with the 'jaws of life' to get people out, but I don't think that device existed yet.
Apparently the bus at front right caught the front left of the roof of bus "B" for Boston forcing it up and beyond the left side, leaving all passengers with their heads on their shoulders. Still I'd bet neither driver walked away.