[jfields]

An alternative strategy to limiting data is to obfuscate it at the source. If a small group of people use from a set of cards and each person pick one at random whenever they need to use it, the cards become little more than dumb tokens that cut the cost of a single trip and just happen to store trip data in the process. A single person's travel habits aren't decipherable unless every card in the set is scraped for data and the results are combined.

Of course, this is effective only if all the cards stay unregistered, and if there isn't a significant monthly (or other periodic) fee per card, unless I'm looking at this situation rather naively. (I live in a rural area without access to mass transportation systems, so I'm not speaking from any kind of personal experience.)