Originally Posted by corporate-wage-slave

It's manually set and has never been reliable. To some extent its purpose is now over now that there are Flight Connection channels to both South and North, plus various other things HAL have done to speed up security. When Connections was North only there was a clear case at certain times of the day to get people to walk down to South, but now they can regulate the Flight Connection flows far more precisely than this sign. It potentially has a value on a few days of the year, e.g. Ski Saturdays. We now rarely see complaints about security queues in T5 when that used to be a regular feature of FT threads.