Originally Posted by bgriff

If you were going to do it, you might split the platforms in half lengthwise, and could have trains where one car was landside and one car was airside (there are similar things on trains at SEA and MCO, among others, to allow arriving international passengers to get from satellite concourses to the terminal as landside passengers while screened airside passengers travel in other cars; FRA and SIN also have interterminal trains where one car is landside passengers while the other car is passengers in the international transit zone). And then the Howard Beach and Jamaica trains would stop only at the landside part of the platform.

It wouldn't have been a half-bad idea to incorporate when the AirTrain was being designed, but it would be tricky to set up now, since you'd need elevator and escalator access to both parts of the platform. T4 would be particularly tricky since the platform is integrated into the building so you'd have to find a place for a new passageway between the train station and the airside area; since the other AirTrain stations are standalone you might be able to just build a new external corridor somewhere that makes the connection. (Of course, in the original design for the AirTrain and T4, T4 itself wasn't even all one security zone; the A and B concourses used to have separate security checkpoints, and the area where the Amex lounge is was a landside area.)