Interstate business routes are roads connecting a central or commercial district of a city or town with an Interstate bypass. These roads typically follow along local streets often along a former U.S. route or state highway that had been replaced by an Interstate. Interstate business route reassurance markers are signed as either loops or spurs using a green shield shaped and numbered like the shield of the parent Interstate highway.
Some states regard Interstate business routes as fully integrated within their state highway system while other states consider them to be either local roads to be maintained by county or municipal authorities or a hybrid of state and local control.
Although the public may differentiate between different business routes by the number of the parent route and the location of the route, there is no uniform naming convention. Each state highway department internally uses its own designations to identify segments within its jurisdiction.
From central Oklahoma westward, the business routes often follow the historic alignment of the former U.S. Route 66 (US 66).
The business loop of Interstate 40 through Needles in San Bernadino County begins at Exit 141 of the combined I-40 and US 95 northwest of town. The loop follows Broadway Avenue to the southeast to Needles Highway, then eastward through an underpass of I-40 into the town center. At N Street, the loop turns southward into the southern part of town where it reconnects with Broadway Ave. The route then continues southeastward to I-40 Exit 144 where it terminates and US 95 continues southward along Broadway. The route largely follows the former route of US 66 through town except where the historic highway's path has since been disrupted by the construction of I-40.
The business loops within Arizona are maintained by the Arizona Department of Transportation (ADOT) and by municipal authorities. Interstate 40 has five business loops within the state located in Seligman, Ash Fork, Flagstaff, Joseph City, and Holbrook and formerly had loops in Kingman, Flagstaff, and Winslow. ADOT identifies Interstate business loops as State Business Routes followed by the number of the parent Interstate. Individual loops along an Interstate are designated by adding parenthetical numbers that increase eastward and northward. Gaps in numbering represent removal of former routes or potential expansion.
State Business Route 40(0) was a former business loop of I-40 at Kingman in Mohave County. The 3.7-mile (6.0 km) loop began at I-40 Exit 48 where US 93 approaches the intersection from the west along Beale Street and joins the Interstate while the loop proceeded eastward along Beale St. After a short distance, the loop joined Andy Devine Avenue which carried the former US 66. The loop turned northward returning to I-40 and US 93 at Exit 53 where the loop terminated, but the roadway continues forward carrying SR 66.
State Business Route 40(1) is a business loop of I-40 at Seligman in Yavapai County. The 41⁄4-mile (6.8 km) loop begins at I-40 Exit 121 on the west end of town and proceeds northward intersecting the former SR 66, a local road still signed as a state route that is a former alignment of US 66, at Chino Avenue. The loop then takes a semicircular path near the Seligman Airport returning to Chino Ave. where the loop turns east through town. At the eastern edge of town, the loop turns south returning to I-40 at Exit 123.:418
State Business Route 40(2) is a business loop of I-40 through Ash Fork in Yavapai County. The 1.5-mile (2.4 km) loop begins at I-40 Exit 145 and proceeds to the northeast along the western edge of town. The loop passes through town as a divided route with eastbound traffic following Park Avenue and westbound traffic routed along Lewis Avenue. The roadways combine on the east end of town, and the loop returns south terminating at I-40 Exit 146. The roadway continues south beyond I-40 as SR 89.:419–420
State Business Route 40(4) is a business loop of I-40 through Flagstaff in Coconino County. The 6.7-mile (10.8 km) loop begins at I-40 Exit 191 west of Flagstaff and enters the city following the former route of US 66. In central Flagstaff, the loop intersects SR 89A at Milton Road. The loop turns north and follows Milton Rd. and then turns east along Santa Fe Avenue before intersecting US 180 at Humphreys Street. The loop continues to the east side of Flagstaff where Santa Fe Ave. diverges carrying the former routes of I‑40 Bus. and US 66 before intersecting US 89. From this intersection, the loop turns southward along Country Club Drive overpassing Santa Fe Ave. and the former routes it conveyed until terminating at I-40 Exit 201.:663–667
State Business Route 40(5) was a former business loop on the east side of the city of Flagstaff in Coconino County. The 4.6-mile (7.4 km) loop began at the combined route of I‑40 Bus. and US 180 and followed Santa Fe Avenue eastward underpassing the current business route. The loop continued along the former US 66 connecting with I-40 and US 180 at Exit 204 for Walnut Canyon Road along the city's eastern edge. The loop was decommissioned in 2008 and returned to the city for maintenance.:423:668
All of the business loops within New Mexico are maintained by the New Mexico Department of Transportation (NMDOT). In New Mexico, Interstate business routes are named independently of their parent Interstate's designation with business loops of Interstate 25 (I-25) numbered between 10–19, those of I‑10 between 20–29, and those of I‑40 between 30–39. New Mexico business loop numbers ascend eastward and northward with gaps in numbering to allow for future designations. Within New Mexico, I-10 currently has business routes in Moriarty, Santa Rosa and Tucumcari.
All of the business loops within Texas are maintained by the Texas Department of Transportation (TxDOT). Interstate 40 has seven business loops in the state, each located in the Panhandle region. Along I-40, TxDOT identifies each business route as Business Interstate 40 followed by an alphabetic suffix. Along Texas Interstates, the alphabetic suffixes on business route names ascend eastward and northward. There are gaps in the alphabetic values to allow for future system expansion. The alphabetic naming suffixes are included as small letters on the bottom of reassurance shields.