The purpose to this idea is to save time at highway toll. Actually if you want to save time (at least in France) you need to have a specific and rented device detecting you and billing you. The current technology could allow the highway company to detect you car registration plate with a camera. This ID could be linked with a registration you have made online of different car you own and a credit card + a phone number.
Car would pass through the toll, be billed and this could be confirmed by an SMS sent to the user.
As a consequence, the system could be faster, not attached with a monthly payment and easier to manage (no hard device to move car to car, return, maintain …)
As all the idea in this category, feel free to comment, and develop, if you become rich with it … don’t forget to help me paying my house !