List of business routes of the Interstate Highway System
The Interstate Highway System of the United States, in addition to being a network of freeways, also includes a number of Business Routes assigned by the American Association of State Highway and Transportation Officials (AASHTO). These routes connect a central or commercial district of a city or town with an Interstate bypass, and are signed with green shields resembling the Interstate Highway shield. The word is used instead of , and, above the number, where the state name is sometimes included, the word or appears. A business loop has both ends as  its "parent", while a business spur has a "dangling end", sometimes running from the end of the Interstate to the downtown area. 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 have to meet Interstate Highway standards and are not considered part of the Interstate Highway System. AASHTO does, however, apply similar standards as to new U.S. Highways, 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 the now-decommissioned Interstate 40 Business in Winston-Salem, North Carolina, and the existing Interstate 80 Business in Sacramento, California. Business Interstates are most often posted in the western states, across the Great Plains and in Michigan. Eastern states generally did not designate business routes, as most of the Interstates paralleled the original U.S. Highways instead of directly replacing them. With the exception of mountainous areas, this left most of the U.S. Highways in place, or as co-signed routes with the parent Interstate, while the former routes were redesignated as local or frontage roads. In contrast , construction of the Interstate system in the western states often directly overlaid the old U.S. Highway, leaving the former road impassable or as a disconnected route. Exceptions were at cities and towns, where the freeway would shift onto a bypass around them. This often left extant segments of old U.S. Highways in place, with a business route designation applied to them as a motorist aid to and from a business district of collection of motorists services. Like auxiliary Interstate Highways, Business Interstates can be repeated from state to state along their route. However, unlike auxiliary Interstate Highways, Business Interstates can  also be repeated in several locations within the same state. List. Defunct routes are listed in italics. Interstate 24. ¹ Downtown Loop I-24 in Paducah, Kentucky was changed to Business Loop I-24 in 2002. Interstate 40. † Business Loop I-40 for Glenrio, Texas is a spur route (at the New Mexico state line it becomes a country road), but is posted as a business loop.