We have seen what a difference the addition of the subway has on arriving and departing passengers, so also implement a train station,
Why it should be implemented:
I would see this as a two platform station, one for arrivals and one for departures, the passengers would approach/leave the station from a sidewalk and a train would arrive 3 times per game hour, first the arrivals doors would open and the passengers would depart and head for the terminal. Then the departing passengers could enter. Each train would have a maximum passenger size (maybe each different, and randomly arriving) and if full the train would depart leaving passengers on the platform waiting for the next train. The track for the station could only begin from a external map tile which would add additional elements to airport planning if you want to implement a station or move elsewhere on the map.