Traversing a total of 3.68 miles (5.92 km), it starts at exit 108 along I-26, it has exits with I-20 (westbound only, signed "Exit 107" as it leads to the I-26 interchange), Colonial Life Boulevard (westbound only) and Greystone Boulevard (to Riverbanks Zoo), before crossing the Broad River on the Timmerman Bridge. Past the bridge is a final interchange with US 21/US 176/US 321 (Huger Street). Entering downtown Columbia, it merges briefly with US 21/US 176/US 321, at Huger Street, before ending at Gadsden Street. It is named the Lester Bates Freeway and is co-signed with US 76 for the entire route.
Construction started on I-126 in 1959 and it was completed in 1961 as a four-lane freeway spur of I-26 which opened at the same time. Around 1980, it was widened to six lanes to from I-26 to Greystone Boulevard and eight lanes from there to Huger Street. By the 1990s, a lane was added eastbound from Colonial Life Boulevard to Greystone Boulevard and westbound from Greystone Boulevard to a new I-20 exit just before its western terminus. The eastern terminus of I-126 has fluctuated between Huger Street and Gadsden Street.
Interstate 126 Business (I-126 Bus) was a boulevard-grade business spur of I-126 along Elmwood Avenue, between Huger Street and Bull Street; in concurrence with US 21/US 76/US 176/US 321. The route was never marked on state, county or city highway maps. Signage proliferated along the westbound route in the late 1970s from Bull Street to Assembly Street, but by 2000 only one sign remained and this was gone by the mid 2000s. At some point[when?], I-126 absorbed part of the business spur from Huger Street to Gadsden Street. It is considered decommissioned as no current state/federal maps list it, nor does any physical signage exist.
^These signs were added with a major signage overhaul on Elmwood Avenue around 1978 when US 21/US 176/US 321 were moved from Assembly Street to Huger Street, SC 215 was removed form the route and SC 48 was extended up Assembly Street to Elmwood Avenue