I was affiliated with the Loop then and since, but no longer, and can respond.

The Loop is insular. A "concerned" local citizen called FRA after hearing about the derailment. They inspected, and found no exceptions on the railroad.

The derailment was caused by very old relay ties - one had a legible date stamp of 1937 on it - allowing the rails to spread under the weight of the train on a tight curve.

dave