U.S. Route 321

U.S. Route 321 (US 321) is a spur of U.S. Route 21. It runs for 516.9 miles (831.9 km) from Hardeeville, South Carolina to Lenoir City, Tennessee; with both serving as southern termini. It reaches its northernmost point at Elizabethton, Tennessee, just northeast of Johnson City. Because of its unusual "north–south–north" routing, U.S. Route 321 intersects both Interstate 40 and U.S. Route 70 three separate times. The highway serves different roles in each state: An alternate route to interstates in South Carolina, a major highway in North Carolina, and a scenic route in Tennessee.

US 321 provides direct access between Savannah and Columbia, serving as an alternate to Interstate 95 and Interstate 26. Starting in Hardeeville, US 321 as a mostly 2 lane highway goes through sparsely populated areas and small towns including Estill, Fairfax, and Denmark, heading in a rather straight and northward direction into the Columbia area, widening to a 5 lane highway right after Neeses, then narrowing down to a 2 lane highway right after the town of North and widening to a 5 lane highway again after Swansea and staying that way until it merges with its parent route US 21 in Dixiana. In Columbia, the route stays concurrent with US 21 through Cayce, over the Congaree River on the Blossom Street Bridge, turning left onto Huger Street, right onto Elmwood Avenue, and left onto North Main Street. The roads separate at Hyatt Park, with US 321 staying west of I-77 and US 21 north of Columbia. The route goes through to communities of Winnsboro, Chester, York, and Clover before entering North Carolina at Bowling Green.

US 321 is an important route in Western North Carolina. It provides an alternative north–south route to I-77, which passes through a busy metropolitan area, and US 221, which is more twisty drive up the Appalachians. Travelers from South Carolina who are going to points west of Charlotte and want to avoid the traffic of I-77 may choose to enter the state on US 321.

The highway traverses through seven counties: Gaston, Lincoln, Catawba, Burke, Caldwell, Watauga, and Avery. US 321 has six control cities: Gastonia, Lincolnton, Hickory, Lenoir, Blowing Rock, and Boone.

US 321 is a multilane highway beginning at the state line. After 7 miles (11 km), it enters the Gastonia area. Traffic on northbound 321 through Gastonia is generally not as heavy as traffic on southbound 321 north of I-85, where it may back up for a couple of miles as drivers wait to turn onto I-85. The state completed a new interchange with I-85 in 2021 which has southbound 321 cross over 321NB at a stoplight just north of I-85. The traffic now enters I-85 northbound with a flyunder entrance ramp over a former railroad right-of-way.

The road becomes a freeway at C. Grier Beam Boulevard in Gastonia, just south of NC 275/NC 279. It remains a freeway until just north of its junction with US 70 in Hickory. The freeway bypasses a number of cities that the old US 321 route once passed through. Today, US 321 Business follows the original 38-mile (61 km) route, which serves Maiden, Newton, and Conover, but the freeway is a more direct route to the mountains, and the business route is generally used by local traffic only.

Traffic is usually heavy between Hickory and Lenoir. The North Carolina Department of Transportation (NCDOT) has a long-term plan to widen the road to six lanes, which is expected to begin after 2020.

North of Lenoir, US 321 is a four-lane divided highway, continuing up the steep escarpment of the Blue Ridge Mountains. Until early 2018, the road was a narrow two-lane highway from near Patterson through Blowing Rock. Work on this area continued for much of the first two decades of the 21st century. The widening of US 321 through Blowing Rock was and continues to be seen as a controversial project. Many residents of the town felt that a four-lane highway would destroy the character of the small town, and they proposed several bypass alternatives. NCDOT selected the widening as its preferred alternative, but added several features such as underground utilities, sidewalks, landscaping, and rock walls to make the widening more palatable to the residents opposed to it. These features were not present on the two-lane highway that was replaced. The final portion of the widening project, at the steepest part of the road just south of Blowing Rock, began in 2012 and was completed in 2018. Some landscaping work remains which will commence in Fall 2018 as its own project, constructed separately for beautification of the route through town.