Trains don't derail or plow through a station barrier in real life -- only in movies. It's possible, I suppose, if the chief engineer has suffered a heart attack or something. Like that elderly subway engineer in The French Connection. In Silver Streak Gene Wilder's heroic George Caldwell, knowing that the throttling engine car is unstoppable, disconnects it from the rest of the train. All to say that the Metro North engineer who allowed a train to smash into the New Canaan end-of-the-line barrier was either unconscious or suffering some kind of seizure or whatever.