U.S. Route 16A (US 16A or U.S. Route 16-Alternate) is a 36.971-mile-long (59.499 km) scenic United States highway. It is an alternate route for US 16. It splits from US 16 in the Black Hills of the southwestern part of the U.S. state of South Dakota. The highway's western terminus is an intersection with US 16, US 385, and South Dakota Highway 89 (SD 89) in Custer, South Dakota. The eastern terminus is at an interchange with US 16 called the Keystone Wye south of Rapid City, South Dakota. Portions of US 16A are known as the Iron Mountain Road.

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