A major road construction project is underway, closing a section of U.S. Highway 16A near Custer to allow for culvert replacements and infrastructure upgrades. The closure affects the stretch between Iron Mountain Road and Custer State Park’s Wildlife Loop and will remain in place until April 2026.
The broader project includes replacing pipe culverts, building gabion walls, and resurfacing 13 miles of highway. Full completion is expected by October 2026.
A detour is in effect via S.D. Highway 36, Ritterberger Road, Cobb Road, LH Road, and Wildlife Loop Road. Drivers should note that six miles of the detour are gravel, and Wildlife Loop Road has a reduced speed limit of 25 mph. S.D. Highway 40 between Hermosa and Keystone is also available as an alternate route.
Custer State Park’s Wildlife Loop and Iron Mountain Road will remain open throughout the project. For maps and updates, visit dot.sd.gov/16a-culverts.
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