MOWBill
On the BNSF the sign is the beginning of the restriction.
So, assuming that applies to the line in question, that means that the speed limit is 30 mph for two miles preceding the start of the curve. That paints a quite different picture indeed.
That means that the NTSB statement that the train was moving 80 in the 30 zone could mean that this overspeeding occured say a mile ahead of the curve, but that the engineer realized his mistake in time to begin braking and considerably slow the train.
That may explain why the wreck damage does not look quite as extensive as one might expect for a train going on the ground at 80 mph. I wonder what the maximum speed is that would allow the train to travel around the curve without derailing. Could it be as low as 60?
If so, he might have braked down to say 63 mph before the train derailed.