Special routes of U.S. Route 21

Beaufort business loop

U.S. Route 21 Business (US 21 Bus) traverses through downtown Beaufort, via Sea Island Parkway, Carteret Street and Boundary Street.

Orangeburg connector route

U.S. Route 21 Connector (US 21 Conn) is an unsigned 1.5 miles (2.4 km) connector route from Broughton Street (US 178 Bus) to Chestnut Street (US 21/US 178), via Park Street and Columbia Road.

Columbia connector route

U.S. Route 21 Connector (US 21 Conn.) is a 2.9-mile-long (4.7 km) 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 76/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. It passes Greek Village, the fraternities and sororities of the University of South Carolina (USC). Right after passing the Carolina Coliseum, it intersects South Carolina Highway 48 (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).

The entire route is in Columbia, Richland County.

Fort Mill business loop

U.S. Route 21 Business (US 21 Bus) traverses through downtown Fort Mill, via Spratt Street, White Street, Old Nations Road, and Springfield Parkway.

Elkin business loop

U.S. Route 21 Business (US 21 Bus) traverses through downtown Jonesville and Elkin, via Main Street and Bridge Street. The route was established after the mainline was realigned east along a completed section of I-77.

Orangeburg business loop 1

U.S. Route 21 Business (US 21 Bus) originally traversed 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 Street and Columbia Street).

Rock Hill business loop

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