South Carolina Highway 170 is a 36.4 mile state highway, connecting the rapidly growing areas of northern Beaufort County with southern portions of Beaufort and Jasper counties. Due to increased population growth, the majority of the road is four lanes wide, with certain areas retaining the original two lane configuration.
Beginning in Beaufort at an angular intersection with U.S. Highway 21, the road is known as the Robert Smalls Parkway for approximately five miles as it travels in a southwesterly direction across Port Royal Island. After intersecting with South Carolina Highway 802, Highway 170 crosses the Broad River over a 1.7 mile 4-lane bridge built in 2004, replacing a previous 2-lane drawbridge. The route crosses Lemon Island and surrounding marshes before crossing over the smaller Chechesee River and enters the southern portion of Beaufort County. This particular stretch is quite scenic, with panoramas of marshes and surrounding islands extending for miles.
Shortly after the intersection with Snake Road and Callawassie Island's entrance road, the route crosses briefly into Jasper County before running exactly along the boundary between Beaufort and Jasper County for approximately eight miles. The route is mostly rural, though new commercial and light industrial development has begun to appear along the Jasper County side of the road.
The route crosses fully into Beaufort County and passes under U.S. Highway 278 at an intersection known locally as McGarvey's Corner and shortly after that intersection is reduced from four to two lanes. It skirts the eastern edge of the Sun City Hilton Head development before intersecting with Bluffton Parkway, which provides direct access to Bluffton. It continues for another two miles before reaching South Carolina Highway 46 at a traffic circle.
Highways 170 and 46 are co-signed for approximately three miles as they cross into Jasper County before splitting at an intersection five miles southeast of downtown Hardeeville. Shortly past that intersection, Alternate Highway 170 splits from the road by continuing straight while Highway 170 makes a right onto Freedom Parkway. Highway 170 continues along the extent of the road before intersecting with U.S. Highway 17 in the unincorporated Limehouse community.
Highways 17 and 170 are co-sigend for approximately two miles on a four lane, divided highway configuration. The highways split after passing by a former truck weigh station, with Highway 17 continuing to Savannah and Highway 170 heading into the Savannah National Wildlife Refuge. The route emerges out of a densely wooded area and crosses nearly two miles of marshes before reaching the Savannah River and the Georgia state line. The road continues onward to Port Wentworth as Georgia State Highway 25.