Here's how I envision it. You grab a ticket from a ticket machine (i.e. brick) with possible point deduction assuming player is in a minigame (also depending how much the player possibly wants to put in the card if the card isn't one time use), then the ticket pops out. Player takes the ticket, goes into a turnstile-esque brick and once swiped, it would tell you the amount left on the card in the chat. Or, the whole card disappears because it is eaten by the machine. The turnstile can also possibly be used backwards when people are leaving the area/subway.
The add-on would work perfectly with the railroad add-on, assuming players made stations.
