said by Crookshanks:EzPass does not require the vehicle to slow down. It will read the transponders at any speed.
I drove on such a route (209 I think?) in Ontario on my way to Toronto. A few months after the fact I received an invoice in the mail (for $45 CAN! They aren't cheap!) for the toll charges that I then paid with a credit card. It was a pretty slick system and worked at full highway speeds without compelling you to slow down as E-ZPass does.
Not sure why we need transponders either, other than it's a legacy structure. Was OCR sufficiently advanced when E-ZPass came onto the scene to read license plates reliably? I'm guessing the answer is no? The technology is there now, at least on the NY Thruway, I've been automatically billed the appropriate amount the handful of times my transponder failed to register for whatever reason.