How the United States highway system works (idea)

Note that this is the numbering system for the United States Interstate system, not the US Highway system. Interstates are called interstates, and are notated I-###, US highways are called US routes and are notated US-###. There is no consistent numbering system for the US highway system. For instance, US 1 runs more-or-less parallel to I-95 for much of its journey up the East coast.