is a 123.9-mile (199.4 km) alternate route of US 17 in South Carolina that travels between Pocotaligo and Georgetown.

It heads north along US 21 through Yemassee, where it passes over CSX Transportation's Charleston Subdivision and then over South Carolina Highway 68 (SC 68).

Due to the presence of a parallel railroad spur along the north side of SC 68, access to and from US 17 Alt./US 21 is only available from bidirectional on/offramps on the southwest and southeast corners of the bridge.

At Moncks Corner, it intersects US 52 and is briefly concurrent with that route as the two cross the Dennis C. Bishop Bridge over the Tail Race Canal of the Cooper River just below Lake Moultrie.

Andrews Memorial Bridge over the Santee River, it joins another concurrency with US 521 in Sampit, and both routes finally terminate at US 17, along with the southern terminus of US 701 in Georgetown.

did exist in South Carolina from 1955 to 1994, from the Georgia state line to Limehouse.

Almost immediately, they cross over Dorchester Creek and the Sawmill Branch Trail and enter a southern part of Summerville.

Just north of the intersection with the northern terminus of Jimbo Road, they leave the city limits.

They cross over Sawmill Branch just before intersecting the southern terminus of both East Carolina Avenue and Berlin G. Myers Parkway.

They cross over East Richardson Avenue and some railroad tracks of Norfolk Southern Railway on an unnamed bridge before intersecting East 3rd North Street at the Senator Randy Scott Intersection.

Truck and SC 165 continue to the northeast and enter the southwestern part of Berkeley County, before curving to the north-northwest.

Truck and SC 165 reach their northern terminus, and the roadway continues as Berkeley County Circle to the north-northwest.