Think of the road network as a production line. Before you get into your car to go to work you are the equivalent of raw material. Once in your car and out on the road you have become WIP (work in progress). When you arrive at your place of work your status has changed to FG (finished goods). Once inside, depending on your job, status, mood, etc. you go to the customer adding value or you go to the FG warehouse collecting dust hoping for someone to buy you.