Massachusetts is working towards this goal statewide:
Under the current system, as near as I can tell, you have to have a plate, a vehicle, in order to get a transponder, but once you have a transponder, you can use it in rental vehicles (by adding the plate to your account for the duration of the rental and then taking the plate back off the account when you are done with it). R. got his transponder through NY when he lived in NH and says that at least at that time, you weren't supposed to use it in rental cars. One hopes that it will become possible to get a transponder without having to have a plate, a car at the time of sign-up.
But you never know. The 520 bridge toll system is transponder free (as near as I can tell), entirely plate based. You can set up accounts, and rentals are handled under "Short Term Account". I think.
One wonders what happens if you use two different ZipCars in the same weekend.
ETA: I don't take the jobs argument (toll takers will lose their jobs taking tolls, altho the states are making an effort to transfer them to other jobs in the transportation department) very seriously, largely because I view toll taking as a hideously dangerous occupation that _should_ be automated out of existence as soon as possible.
ETAYA: New Hampshire has been reducing staffing at low use times of day (night).
You still owe the toll, even if you don't have a transponder. If you don't have change, you can pick up an envelope and mail in your toll.
ETA Still More: Maine has added some high speed tolling, but this coverage gives an indication of how dangerous this transitional period between stop-and-pay and electronic drive-thru (fast or slow) tolling can be to users as well as toll takers.
"The authority's greatest fear -- it has happened in other states -- is that a cash-paying driver could mistakenly enter a highway-speed toll lane and try to stop, back up and pull over after realizing their error.
Morin said that has been seen at the York toll plaza, where drivers who mistakenly get into an E-ZPass lane stop and walk over to another booth to pay a toll taker."
There is some serious fucked-up-stupid here in New England. I saw a teenager crossing Highway 3 in Nashua (probably going from one high school to the other?). I cannot tell you how many times I have seen people miss their exit, pull over, and then back up to take it. I spent three decades in the Seattle area without _ever_ seeing either behavior (half that time I was a driver), but while it continues to strike me as irremediably bad judgment, I've started to anticipate which cars are going to do something foolish at exits.