The Ring Road connects all the different regions of the main location together. Each exit from the Ring Road to a region is equipped with a Transportation Hub. Hubs earn additional income by gathering taxes for the particular region. In order to begin working, hubs need to be connected to other working hubs. The Nephilim Mall is part of the City Center, and starts working as a functional hub as soon as it is built.
 
So what exactly do the hubs do? Taxes earned from a region accumulate in the hub. Upgrade hubs to increase the amount of taxes gathered from the different regions, as well as how much money can be stored in a hub at a time. Keep in mind that before you start building the Ring Road, you will need to build the transportation overpass.
 
Have fun playing the game!