Source: Catullus 5
Police, prosecutors, and divorce attorneys use records of highway toll transponders in court all the time. Any day now, they’ll start using CharlieCard records the same way. If they haven’t already. I’d like none of that for me, thanks. I’ll keep my CharlieCards anonymous.

Fund them only with cash, and don’t “register” my account with the MBTA. And since I don’t need a monthly flat-price pass, I’ve gone ahead and obtained TWO cards, so I can mix it up. Use one for going inbound, for instance, and the other for going outbound. That way no one can even prove that the same person made both legs of the trip. This greatly reduces the quantity of information they can collect. The MBTA system doesn’t know when or where you get off the subway, but by using the same card twice it’s easy enough for them to make an educated guess. If a card pays a fare at station A and another at station B two hours later, it’s a good bet that B is where this person got off the first time. Furthermore, he probably returned to station A, and he probably lives near there. That’s a lot of information. I’d rather mix it up so they only get one data point. They won’t know if A is where I come from or where I go to.

There are some ways this scheme could fail. “They” could surveil me at the turnstile, and then associate my face with the system’s record of which card was presented at that same time. They could mine their data looking for repeated instances of some card X being used exactly once, followed by another card Y also being used exactly once. If a pattern appears for two cards X and Y, they can conclude that the same person holds both cards. Or they could simply search or arrest me and discover both cards. But regardless, this is definitely an upgrade over “Hello, my name is Bob Q. Subject, and this is the card with which I’ll create exhaustive records of all my travel from this day forth.”

P.S. Anyone who makes the argument about “if you’re doing nothing wrong, what do you have to hide?” deserves to be pimp-slapped.

RFID fare cards for the Boston subway, for you out-of-towners