Ques - Why do Loco Pilots wave green flags when two trains are crossing each other?
Answer - It is to indicate that the circumstances of the track on which the opposing train is going is ok - to the extent practical. If it is not ok then the oncoming train needs to be stopped immediately.
Now as per news article-click here
Question arises that LP of 74643 shouldn't have given red signal to LP of 13006 as the line of 13006 was also not clear? Further accident must have been avoided.