Detailed text transcripts for TV channel - CNN - 20171219:01:47:00
Know, with the speed that -- or with the energy that we can see here in this crash, it tells us they weren't going at a low speed. you always want the cars to remain upright. that's the best outcome for passengers. but in this case, falling from that bridge or going into the woods where they can hit other things, again, those are all not outcomes that you want to see, especially train cars flipped over. >> there's been a lot of talk about ptc, positive train control. can you explain exactly what that is and how that might have been able to make a difference in this crash? >> so, positive train...