According to the Warren Commission Report, the train was struck by a magic rock which shattered the windshield, turned in midair and pushed the throttle forward, turned again and hit the emergency brake, then hit the driver in the head rendering him unconscious, turned once more and exited through the rear crew door. Google earth shows a small grassy knoll just before the turn in the track, just east of the knoll you can see a woman in a black burqua.
Ah yes... the Elizabeth Warren...report!!