U.S. investigators say deadly Amtrak train crash preventable | Digital Short

Federal investigators are trying to figure out why a switch was in the wrong position, sending an Amtrak train into a freight train and killing a conductor and an engineer in South Carolina. But they already know what could have prevented the wreck that injured more than 100 passengers — a GPS-based system called “positive train control” that knows the location of all trains and the positions of all switches in an area to prevent the kind of human error that can put two trains on the same track.