Where three escalators are in parallel, two of them (the middle one and the one on one side) run in one direction and the remaining one (the one on the other side) runs in the other direction. The middle one should operate in the direction that most helps that station's pattern of foot traffic, even if that means running in one direction for the morning rush hour and in the other direction for the evening rush.
Downtown stations would have two outbound escalators (to drop off incoming office workers at street level) and just one inbound escalator, during morning rush; they would then have two inbound escalators (to pick up outgoing office workers from street level) and just one outbound escalator, in the evening. Stations in residential neighborhoods would be set up conversely. In either case, the middle escalator would switch during mid-day.
This stands in contrast to the practice of many stations today. For example, in Farragut North, the two permanent outbound escalators work well in the morning, helping many people exit easily, but hinder in the evening, as many people must file into the single inbound escalator. The middle escalator should switch from outbound to inbound during the middle of the day, as described above.