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.
Highway systems by country
The term "Highways" in the U.S. even includes major paved roads that serve purposes similar to those of the U.S. Highways or Interstate Highways, but which are completely designed, paid for, and maintained by state or local governments. An example of this is Tennessee Highway 840, which is a long, partially completed "urban bypass" of Nashville, TN that is a multi-lane, controlled-access highway entirely designed and paid for by Tennessee. Much of the traffic on it will eventually come from Interstate 40, completely avoid the big city, and then return to Interstate 40. Incidentally, Tennessee-840 also has connections with Interstate 24 and Interstate 65, where both of the freeway interchanges are already finished, as well as the eastern interchange with Interstate 40.