From the animation they showed, it seemed the cars immediately piled up, causing some to veer left and some right.
The one in Philadelphia looked like this. I was not thinking of it when I made my comments here. I just know what centrifugal force is like.
Every car going around that curve would have had massive energy built up headed toward the outside of the curve. I remain unconvinced you overcome that with the accordion theory, but I'm not convinced that can't be a factor. I'll come back.
Here's a picture to think about in the meantime.
Excessive speed hits curve (in this instance 105 mph approximately)
How many cars do you see on the inside of the curve?