Yes, the most common is N-system, which you see frequently. They are rectangular with enclosed lenses. They are just tracking your movement 1984 style by reading your license plate. Sometimes I pick up an infrared signal (904 nm) when passing right under with my Valentine 1.

ETC also has checkpoints as you approach a toll. Maybe if you don't have a card in your reader it gives you a warning. It shows up as ETC OK on my display. It also charges your card at points when you are leaving the Shutoko to another highway, e.g. after the Takaido exit before you continue on the #4 Chuo expressway.

Before Jan 1 2012 the Shutoko was flat fee (700 yen) but now it's 500-900 yen depending on distance. So it works a bit differently now.

There are speed cameras. They look like boxes with a round lens and also tend to have a light that goes off if they detect you. I have heard that you have go 40 km/h over to trigger one.

http://www.accessj.com/2013/05/autom...-in-japan.html

The one that I notice is the LH system. Notice the lamp that will illuminate.