The way these transponders work now, anyone can scan and detect your identity. The transponder will happily wake up and reply to anything that sends an activation signal. So carrying a transponder makes it possible for the government to track you everywhere you go, and in fact, RFID readers are now mounted along highways, not just at toll gates. The justification for installing these other RFID readers was to measure traffic flow. But they collect more information than they need to do that — each transponder sends a unique signal, so these readers are picking up identifiable tracking information all day long.
The problem is that there's no way to turn the FasTrak transponders off. They're ready to transmit all the time. Some drivers use the makeshift solution of stuffing the transponder in a mylar bag to shield it from radio signals. But why not just have a switch on the darned thing? That seems like a simple, easy solution. Reach up and press the button on your transponder (to make it capable of waking up) as you drive through a toll gate. The rest of the time, your privacy is respected. Paying tolls remains easy for drivers, the government get its tolls, traffic keeps flowing, and everyone gets voluntary control over their privacy.
I think they should just make transponders with buttons.