We often see that a two-story overpass needs to be built at the crossroads in both vertical and horizontal directions. Then, if three roads cross, or there are six directions from the center of the intersection, what level should the overpass be? If a center radiates 10 roads, how many grade overpasses will be built? The Arc de Triomphe in Paris, France, radiating around 10 roads. What overpass does it use? Generally speaking, two-story overpass is needed when two roads cross, three-story overpass is needed when three roads cross, and so on, radiating around 10 roads, that is, five-story overpass is needed when five roads cross. However, the Arc de Triomphe did not build a multi-storey overpass, but used the central loop to communicate with the 10 road. Cars on all roads should gather on the circular road in the central area, drive counterclockwise and then drive in the right direction. Therefore, it is a practical and simple method to use circular roads when multiple roads are gathered together.