Heh, interesting. My apologies for misunderstanding. After doing a little research, I realize that while TxTag is the statewide interoperable transponder, any pay-by-plate arrangements are made with each individual toll facility. ZipCash is only for NTTA facilities. Austin area toll roads have a different arrangement. But Houston has nothing. Shame on them.
Although we actually got into this debate at a NCUTCD meeting a few years ago when someone asked "what the heck is the difference between a 'processing fee' and a 'fine' for using a toll road without a transponder?" This was a very important discussion topic, since the signing for one vs. the other is very different (the former is signed like a toll road that accepts cash, since theoretically you need not warn anyone in advance that no cash option exists if they will receive a bill...while the later is signed as "XXX Toll Pass Only"). So long as the "fine" doesn't have any points attached (they couldn't, as they have no idea who was driving the vehicle), isn't it essentially a processing fee? The other side said it was an issue of order of magnitude of the mark-up, but no one could really seem to draw the line at what constituted a fine vs. a processing fee. For example, "the rules" say "thou shalt not drive on the I-495 Express Lanes without an E-ZPass." If you do and Transurban has to track you down, you'll pay a $12 "fine" on top of the toll amount. However if you go to Transurban within 5 days of your mis-deed, provide your credit card number, license plate number, and approximate date of your "violation", you'll only pay $1.50 on top of your toll. Is this a "fine" for misuse of the lanes? Or is this just a convenience fee for those who might be in a rush once a year and don't have E-ZPass? I would certainly argue the latter, and I in fact, have encouraged people to give the lanes a try before bothering to sign up for E-ZPass, and to only sign up if they think they'll use the Express Lanes regularly. E-ZPass in Virginia and Maryland have monthly fees, which could easily come out to be more than a measly $1.50 "fine" for using the lanes without one.
Then lets look at Quebec on the A-25. Assuming they can find you (those with US plates have supposidly been able to use the A-25 for free), they tack on a $5.00 "processing fee" onto the toll. I mean, lets think about this. Montreal is not exceptionally wealthy compared to DC...yet Quebec considers $5.00 to be a "processing fee" while Virginia considers $1.50 to be a "fine". Something doesn't add up. Don't even get me started about using an all-electronic toll facility in a rental car....some of their "processing fees" will make any "fine" levied by a toll agency for using the road without a transponder in your own car look like peanuts.
To bring this back on topic...the rental car issue could be a challenge for Tobin Bridge and the Harbor Tunnels being so close to Logan Airport. How will the rental car agencies ensure that every car leaving their lot is equipped with a toll transponder? Keep in mind that the rental car toll programs (PlatePass, Rent-A-Toll, etc.) work in most states by way of photo capture of license plates, but they WILL NOT WORK in E-ZPass territory without a physical transponder box in the vehicle. All of the brochures explicitely state this. So the guy who drives his rental car from San Francisco to Boston, will that car have an E-ZPass transponder in it? (it is still un-clear if rental agencies equip all of their cars with E-ZPass transponders, even the ones from, say, the West Coast). If not, how will the next renter who gets stuck with that car get it back into Boston if there is no way to pay cash, and no way to participate in the rental car toll program without a transponder? And people wonder why I carry my own toll transponder with me when I fly somewhere far away...I'm sure the pilot would have a fit if he/she knew, seeing as it is a "portable electronic device" that can't be turned off!