List of Interstate Highways
There are 70 primary Interstate Highways in the Interstate Highway System, a network of controlled-access freeways in the United States. They are assigned one- or two-digit route numbers, whereas their associated "auxiliary" Interstate Highways receive three-digit route numbers. Typically, odd-numbered Interstates run south-north, with lower numbers in the west and higher numbers in the east; even-numbered Interstates run west-east, with lower numbers in the south and higher numbers in the north. Highways whose route numbers are divisible by "5" usually represent major coast-to-coast or border-to-border routes (ex. I-10 travels from Santa Monica, California, to Jacksonville, Florida, traveling from the Pacific to Atlantic oceans). Additionally, auxiliary highways have their numbering system where a different number prefixes the number of its parent highway.
Numbered highways in the United States
Highways in the United States are split into at least four different types of systems: Interstate Highways, U.S. Highways, state highways, and county highways. Highways are generally organized by a route number or letter. These designations are generally displayed along the route by means of a highway shield. Each system has its own unique shield design that will allow quick identification to which system the route belongs. Below is a list of the different highway shields used throughout the United States.