lol I just googled it and it turns out spracne is right. I wonder who's getting all those bills. hopefully we're paying them. suppose I should stop driving on the express lanes around DFW just for fun. 
Where is the vehicle registered? They will send the bill to the address on the registration.
one of my company's offices in Kansas somewhere I suppose. I've never looked at the registration. I'm guessing some administrative assistant somewhere is just getting tons of bills from my driving and just paying them. debating on ordering a tolltag so the bills come to me and I can put them on my amex or just continuing to ride this thing and see what happens.
I drive on the dfw toll ways all the time and have never gotten a bill. Spracne doesn't know what he's talking about. Denver will hunt you down, however.
this is what the NTTA website says:
What about vehicles with out-of-state license plates?
NTTA currently partners with a third party to acquire out-of-state vehicle information. NTTA aggressively pursues all tolls owed, whether the vehicle is registered in Texas or another state.
I've never gotten a bill either but that's what it says
