My money is on texting and driving, especially since a warrant was just issued to search the phone. He claims no memory of the accident, but was obviously accelerating prior to the accident, and had time to realize it and hit the e-brakes.
This is actually one of the more advanced lines we have, other than automatic systems, it was in good shape compared to most others, just that nothing could make the corner at that speed. Personally, I see no reason why these forms of transportation cannot be fully automated much quicker and easier than cars, there are many trains existing that have no operators at all. Cars should be the last thing to automate, trains, planes and trucks first.