Special routes of U.S. Route 21

Several special routes of U.S. Route 21 (US 21) exist. In order from south to north, they are as follows.

Beaufort business loop
U.S. Highway 21 Business (US 21 Bus.) is a 5.400 mi business route in Beaufort, South Carolina, that travels along Sea Island Parkway, Carteret Street, and Boundary Street.

Orangeburg business loop 1
U.S. Highway 21 Business (US 21 Bus.) originally traversed Orangeburg, South Carolina, along Broughton Street (in concurrency with US 178 Bus.), Park Street, and Columbia Road. In 1967, the business loop was decommissioned after the establishment of the second business loop through Orangeburg; the old alignment continues as US 178 Bus. (Broughton Street) and US 21 Conn. (Park and Columbia streets).

Orangeburg business loop 2
U.S. Highway 21 Business (US 21 Bus.) is a 2.730 mi business route of US 21 in Orangeburg, South Carolina. It begins at the intersection of US 21 and South Carolina Highway 4 (SC 4) and then traverses along parts of Charleston Highway and Magnolia Street, before ending at Chestnut Street (US 21).

Orangeburg connector route
U.S. Highway 21 Connector (US 21 Conn.) is a 1.480 mi connector route of US 21 in Orangeburg, South Carolina, that is unsigned. It travels from Broughton Street (US 178 Bus.) to Chestnut Street (US 21/US 178), via Park Street and Columbia Road.

West Columbia connector route
U.S. Highway 21 Connector (US 21 Conn.) is a 0.850 mi connector route of US 21 that exists entirely within the city limits of West Columbia, South Carolina. It connects US 21/US 176/US 321, from where they curve off of Charleston Highway and onto Knox Abbott Drive, with US 1. It shares the Charleston Highway name with US 21/US 176/US 321 and is an unsigned highway.

Major intersections

Columbia connector route
U.S. Highway 21 Connector (US 21 Conn.) is a 2.930 mi connector route of US 21 that is an unsigned highway. It is located in the west-central part of Richland County and entirely within the city limits of Columbia in the U.S. state of South Carolina. It connects US 21/US 176/US 321 with US 76/US 378. It is concurrent with US 76 Conn. for its entire length.

It begins at an intersection with US 21/US 176/US 321 (Blossom Street/Huger Street). It travels to the east-northeast on Blossom Street. It crosses over some railroad tracks of CSX Transportation. It passes Greek Village, the fraternities and sororities of the University of South Carolina (USC). Right after passing Carolina Coliseum, it intersects SC 48 (Assembly Street). The highway passes the Carolina Community Garden at the Honors Residence Hall. Then, it passes the Thomas Cooper Library and then the Booker T. Washington Auditorium. It curves to the northeast and travels along the northwestern edge of Maxcy Gregg Park. This is southeast of the USC tennis courts at Blossom Street. The connector curves to the east and travels under a railroad bridge that carries railroad tracks of Norfolk Southern Railway. It curves to the southeast. At the intersection with Saluda Avenue, the highway turns left and travels to the northeast. One block later, at Devine Street, it turns right and travels to the east-northeast. At an intersection with Harden Street, it curves to the east-southeast and travels through a retail area before meeting its northern terminus, an intersection with US 76/US 378 (Millwood Avenue/Devine Street).

Major intersections

Ridgeway connector route
U.S. Highway 21 Connector (US 21 Conn.) is a connector route that partially travels through the western part of Ridgeway, South Carolina, which is in the southeastern part of Fairfield County. It is known as Coleman Highway and is an unsigned highway. It begins at an intersection with US 21 just southeast of Ridgeway. It travels to the northwest and enters the town. It then curves to the west-northwest before leaving the city limits. Then, it curves to the west before reaching its northern terminus, an intersection with SC 34.

Fort Mill business loop
U.S. Highway 21 Business (US 21 Bus.) traverses through downtown Fort Mill, South Carolina, via Spratt Street, White Street, Old Nation Road, and Springfield Parkway.

Rock Hill business loop
U.S. Highway 21 Business (US 21 Bus.) originally traversed along Main Street, Albright Road, Black Street, Oakland Avenue, and Cherry Road, through downtown Rock Hill, South Carolina. It was decommissioned at the request of Rock Hill to gain ownership and maintenance oversight from the state.

Jonesville–Elkin business loop
U.S. Highway 21 Business (US 21 Bus.) traverses through downtown Jonesville and Elkin, North Carolina, via Main and Bridge streets. The route was established after the mainline was realigned east along a completed section of Interstate 77 (I-77).

Sparta truck route
U.S. Highway 21 Truck (US 21 Truck) is an alternate route for trucks to bypass the downtown central business district of Sparta, North Carolina, and allows truck traffic to travel on and off North Carolina Highway 18 (NC 18). The 1.68 mi route follows along the Sparta Parkway, which bypasses west from mainline US 21, connecting with Grandview Drive and West Whitehead Street (NC 18).

Bluefield bypass route
U.S. Route 21 Bypass (US 21 Byp.) originally traveled through downtown Bluefield, West Virginia, utilizing Bluefield and Princeton avenues, but, as US 21 no longer serves north of Wytheville, Virginia, there is not a US 21 bypass. Prior to the Interstate Highway System, US 21 ran from Ohio to Florida. Once I-77 was built, there was no longer a need for US 21, and it made its terminus Wytheville.