Amtrak and the FRA did extensive studies on one vs. two in the cab and found that errors in train handling (i.e. run signals, missed slow orders etc..) happened as much as 3 times more frequently with two people in the cab. Study has been repeated many times with similar results. The problem was found that two people in the cab begin to talk to each other and often, get into lengthy bull sessions about---football, hunting, the spouse, vacations and what have you---thus causing distractions that don't happen when the engineer is alone in the cab. If we must have a second set of eyes in the cab, we will have to figure out a 'cone of silence' between them or the same old problems will reappear. A secondary factor was found to be that there was a reduced level of attention paid by both people when they were relaxed in the secure notion that if "I miss it, he will see it" and video in the cab found that even if the employees were not talking to each other, there was a reduced level of attention paid by both workers when two were in the cab. (as noted by less time facing forward by employees studied).