U.S. Route 17 Alternate

US 17 Alt. starts at the northern terminus of the US 17/US 21 concurrency near Pocotaligo as a two-lane highway. 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. The concurrency continues until US 21 splits off on its own to the northwest. From here, it runs through Hendersonville, and then Walterboro, where it merges with SC 63, becomes the northern terminus of SC 303, and the southern terminus of US 15. From that point, US 17 Alt. moves away from Interstate 95 (I-95), running along the southeast side of Lowcountry Regional Airport and moving further northeast. In Summerville, it intersects US 78, has an interchange with I-26, and intersects US 176. 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. After crossing the W.H. 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.[8]

US 17 Alt. was established in 1951 as a renumbering of mainline US 17 from near Pocotaligo to Walterboro, SC 64 from Walterboro to Moncks Corner, SC 179 from Moncks Corner to Jamestown, and SC 528 north of Jamestown to Sampit. US 17 Alt. was also overlapped with US 52 in Moncks Corner, SC 41 around Jamestown, and US 521 between Sampit and Georgetown.[9][10][11][12][13][14][15][16][17][18]

The first section to be widened to four lanes was in 1970 from US 78 to I-26. This followed with four-lane sections in Georgetown (1974), its concurrency with US 52 in Moncks Corner (1975), and its concurrency with SC 64 in Walterboro (1979). Since the late 1990s, US 17 Alt. has been widening slowly into four-lane from I-26 toward Moncks Corner.

A second US 17 Alt. did exist in South Carolina from 1955 to 1994, from the Georgia state line to Limehouse. Today, it is part of mainline US 17.

U.S. Highway 17 Alternate Truck (US 17 Alt. Truck) is a 8.242-mile-long (13.264 km) truck route for US 17 Alt., mostly within the city limits of Summerville. It serves portions of southeastern Dorchester County and a very brief portion of southwestern Berkeley County. It is entirely concurrent with SC 642 and SC 165 for its entire length.

US 17 Alt. Truck begins at an intersection with US 17 Alt. southwest of Summerville, in the southeastern part of Dorchester County. This intersection is also the western terminus of SC 642. US 17 Alt. Truck and SC 642 travel on Dorchester Road nearly in a due east direction before curving to an east-southeast direction. In Limehouse Crossroads, they intersect SC 165 (Bacons Bridge Road). US 17 Alt. Truck leaves SC 642 and turns left onto SC 165. The two highways travel to the north-northeast. 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 intersect the western terminus of Mikel Drive and the eastern terminus of Edisto Drive, which leads to Flowertown Elementary and Newington Elementary schools. A short distance later, they reenter Summerville. Almost immediately, they intersect the northern terminus of Trolley Road. Here, US 17 Alt. Truck and SC 165, as well as the Bacons Bridge Road name, turn left. They proceed to the north-northwest. They cross over Sawmill Branch just before intersecting the southern terminus of both East Carolina Avenue and Berlin G. Myers Parkway. US 17 Alt. Truck and SC 165 turns right onto the parkway and travel to the northeast. They pass Summerville Elementary School and Rollings Middle School of the Arts. 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. This road leads to the Summerville Visitors Center. Almost immediately is an intersection with US 78 (East 5th North Street). US 17 Alt. Truck and SC 165 continue to the northeast and enter the southwestern part of Berkeley County, before curving to the north-northwest. They intersect US 17 Alt. (North Main Street). Here, both US 17 Alt. Truck and SC 165 reach their northern terminus, and the roadway continues as Berkeley County Circle to the north-northwest.[22]

County	Location	mi[19][20][21]	km	Destinations	Notes
Dorchester	​	0.000	0.000	US 17 Alt. / SC 642 begins – Walterboro, Bamberg, Summerville	Southern end of SC 642 concurrency; southern terminus of US 17 Alt. Trk.; western terminus of SC 642
	Limehouse Crossroads	2.832	4.558	SC 165 south (Bacons Bridge Road) / SC 642 east (Dorchester Road) – Charleston, Charleston A.F.B.	Northern end of SC 642 concurrency; southern end of SC 165 concurrency
	Summerville	5.512	8.871	East Carolina Avenue north to US 17 Alt.	Southern terminus of East Carolina Avenue
		7.392	11.896	US 78 (East 5th North Street) – St. George, Charleston
Berkeley		8.242	13.264	US 17 Alt. (North Main Street) / SC 165 ends to I-26 / Berkeley Circle north – Walterboro, Moncks Corner	Northern end of SC 165 concurrency; northern terminus of US 17 Alt. Trk./SC 165; southern terminus of Berkeley Circle
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

• Special routes of U.S. Route 17

Wikimedia Commons has media related to U.S. Route 17 Alternate (South Carolina).

• US 17 Alternate at Virginia Highways' South Carolina Highway Annex (Mapmikey's South Carolina Highways Page)