Exactly. I'm guessing it'll probably generate some kind of key based on an algorithm that includes maybe the time, gantry ID, frequency etc. to allow them to link back to the transaction that gets generated. All in all I'm sure the whole thing will be quite bulletproof (remember, the ANC had nothing to do with the design of the system

)
I'm also guessing those tags are active RFID's?
Passive will be too weak and would need a massive coil on those Gantries to generate enough electromagnetic energy to get a powerful enough response given the distance, speed and fact that they're enclosed in a vehicle.
Anyone who has a tag should post some pics, would like to see what they look like.
EDIT: Is this the one?
http://www.kapsch.net/en/ktc/downloads/files/brochures/Kapsch-KTC-DS-OBU-TS3203_10B-EN.pdf