Originally Posted by
guv1976
It doesn't matter where the initial swipe is. You can reenter the system at Lexington/63rd Street or Lexington/59th Street for free within about two hours of the initial swipe of a pay-per-ride Metrocard.
You can also do this at Court Square (G train) and Courthouse Square (7 train) in Long Island City.
You have 2:18 minutes for the free transfer (though it is advertised as 2:00 hours).
As for how this is kept track, your MetroCard serial number is tracked when you swipe in at any station. When you swipe in again at one of the four aforementioned stations (Lex; 59 St; Court Square; Courthouse Sq), little hamsters operating the MetroCard computer are trained to let you in for free, essentially an exception to charging your MetroCard again.
Once upon a time, there was supposed to be an underground passageway linking 59 Street Station (4, 5, 6, N, Q, R, W trains) to the Lexington Av Station (F train), but this was eliminated as a cost cutting exercise. For that matter, there was also supposed to a 3 Avenue exit at Lexington Av Station, but that too fell to the budgetary axe. It has been mined and excavated, but left in an unfinished state.
Someday, it is supposed to be completed as part of the Second Avenue Subway, a project taking longer to build than the original subway line.