In CA all cars, passenger trucks and vans are sent two plates: one for the front and one for the back and they must be mounted on the car, although they don't enforce it in many places, but if they pull you over for a plate violation, you have 10 days to get it on your car and get it signed off. Semi's, motorcycles and trailers are sent one plate, with motorcycles and trailers having to mount them on the rear and semi's plate is mounted to the front.
California is slowly getting toll roads that are privately financed as well as HOV lanes, but there isn't many of them. I've driven in the Houston and Dallas/Ft Worth areas and never driven on a toll road. New York State has a fair amount of toll roads and they take it one step further, they time you between toll booths and if you get to the next one too fast you not only pay the toll, but are given a speeding ticket as well.