Just my $.02 on the Amtrak issue…

What if the engineer got sprayed with glass, instinctively reacts to it and is temporarilly distracted? Also, can he have — for some reason — mistaken the acceleration and braking levers in that sort of scenario?

Another thought which has occured to me is that braking a train does put load on the track, especially if emergency braking. A weak, poorly maintaned, spot might crack from the strain, and track breaks are known causes of derailings.