The route begins as a four-lane highway, splitting from U.S. Highway 1 where it is known as Jarvis Klapman Boulevard. Through West Columbia, the highway has a mix of at-grade intersections and interchanges. It crosses the Congaree River on the Jefferson Davis McMahan Bridge headed into downtown Columbia. For a stretch in Columbia, the highway splits into a one way pair separated by a city block: Hampton Street and Park Street for eastbound traffic, and Taylor Street and Williams Street for westbound traffic. Continuing east, the route keeps the name Taylor Street. After its intersection with US 1, the road changes its name to Forest Drive as it passes through Forest Acres. After a sharp turn at the unsigned Spur SC 12, the road is known as Percival Road, then Fort Jackson Road. North and east of downtown Columbia, the route runs next to Fort Jackson and parallel to I-77 then I-20. The route traverses through rural land before reaching its terminus at US 601 near I-20's exit 92. Two unsigned special routes of SC 12 exist:
SC 12 Connector follows 9th Street in West Columbia from US 1 to US 378. It is and has an interchange with SC 12 at its midpoint.
SC 12 Spur is a extension of Forest Drive from SC 12 to the entrance of Fort Jackson within the city limits of Columbia. It has one intersection with shopping centers access roads before interchanging I-77 at its exit 12. Past I-77, the road name becomes Strom Thurmond Boulevard and ends at the main gate to Fort Jackson.
History
Previous designations
There have been two previous versions of SC 12. The first version ran from the 5th Street Bridge at the Georgia-South Carolina state line near Augusta, Georgia, to Aiken, Leesville, and Lexington, South Carolina before ending in West Columbia. Today, this route is marked as US 1 from the state line to West Columbia, which was assigned the route in 1927. SC 12 was dropped from the route in 1928, the year afterwards. The second former route of SC 12 was established between 1928 and 1931. The route ran from what is now US 521 between Lancaster and Fort Mill for to the North Carolina state line near Waxhaw, North Carolina, at what was then NC 25. In 1934, North Carolina changed NC 25 to NC 75, and South Carolina renumbered SC 12 to SC 75 four years later, in 1938.
