VIDEO: The collision of three Norfolk Southern trains in Pennsylvania early this month highlights the shortcomings of the automated braking system that was created to prevent such crashes. None of the circumstances the National Transportation Safety Board described Tuesday in its preliminary report on the March 2 derailment would have triggered the automated positive train control system to stop the trains. Not only was the system incapable of stopping the second train before it smashed into the back of a stopped train, but it also couldn't stop the third train. It ran into the derailed cars blockings its track when it arrived less than a minute later. "PTC today has not generally been designed to protect them in that situation," railroad safety expert Chris Barkan said.