We have an iPass unit (Indiana) that we velcro in either our truck or car... whichever one we're using at the time. In the Indiana system, we were told that we needed to register both vehicle's in their system. Works from Illinois to the Northeast, and south through West Virginia. Not compatible with Florida's system, but I read somewhere that this may change. When towing, the toll gate automatically registers the number of axles and charges accordingly. We were on many toll roads last September between Mass and Maryland (DC area) and really appreciated not having to stop at all of the toll booths. Was never charged in error either (as far as I can tell). Wouldn't go without one.
