guy was probably sleeping, and woke up just in time to hit the brakes when he realized he was gong that fast
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OR...he was doing a “GermanWings” type of suicide attempt and chickened out at the last instant and tried to brake.
I've read other posts that those in-the-know say the easiest way to cause a derailment is to accelerate and then brake hard into a corner - causes the train to accordion and derail. I think he meant to crash, and didn't mean to survive the carnage.