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.
List of business routes of the Interstate Highway System
As the main purpose of a Business Interstate is to serve a downtown area, it is typically routed on surface roads. Thus Business Interstates do not meet Interstate Highway standards. AASHTO does, however, apply similar standards as to new U.S. Routes, requiring a new Business Interstate to meet certain design standards. Business Interstates are also sometimes routed onto freeways that were once designated as mainline Interstates themselves (such as Interstate 40 Business in Winston-Salem, North Carolina and Interstate 80 Business in Sacramento, California).