The deal with collecting on a basically per-mile basis makes such roads toll roads. For any State that adopts this it effectively makes all roads in the State into Toll Roads.
This initiative aside, toll roads in the NW are almost nonexistent. I think there are none whatsoever in Oregon. Washington State has tolls on ferries, a couple of bridges, and then there are the voluntary "Lexus Lanes", so the type-A's can pay a toll to drive in a few HOV lanes they would otherwise be denied legal access to. (I have no clue how the state manages to properly administer this last weirdness.)
As one goes East, of course, it becomes slowly more and more common (there are some in the Denver area even). At a gross level, it seems like tolls seem to gravitate around 10 cents per mile. In most states this is in addition to gas taxes already paid by the operators.
I recently spent a few days in the Chicago area. Getting around the area constantly involved figuring out how to have correct change for the tolls. For out-of-towners like us paying cash, lo and behold I found it ran us right at 10 cents per mile. Though apparently for those with EZ-pass transponders it's about half that. Nevertheless it was in addition to state gas taxes. We were driving a rented Nissan Altima (nice car, got about 38 MPG). So to drive 38 miles we spent about $3.80 for the gallon of gas we would use PLUS $3.80 in tolls. So it was equivalent to paying $7.60 per gallon of gasoline.
