CNN Anderson Cooper 360 May 14, 2015 03:12:00
Going too fast. they had dead man switches on the train and all this discussion about a positive train control, this is actually a warning system through a series of transponders that would communicate about two to three miles apart to a receiver on the locomotive if the information being communitycated to the train if they were going too fast for instance 106 in a 50 mile-per-hour zone, then a buzzer would go off, alerting the engineer and he would take action and if he didnt then the computers...
Source: archive.org