>> like you in your car. >> sure. is it possible that the speed can just get away from you? it does in a car you've done that driving your own car you realize you better back off i've been going too fast. is that the same type of effect that can happen in a locomotive. >> usually when that happens that's a few miles an hour over the speed limit, not 50 or more. >> if the train had been going normally we've been hearing a lot about this positive train control. let's say something had gone wrong. a heart attack of the engineer of the locomotive something else caused him to lose his ability to control the speed. would positive train control here make a difference? >> it would have made a difference. it would have slowed the train when it recognized that it wasn't braking for this curve. it would have been computed into the system so that any train traveling at any speed would recognize what speed it was