RAPID CITY, S.D. – A significant road construction project begin today, Monday the 6th, that will close a section of U.S. Highway 16A near Custer, impacting travel in the southern Black Hills. The closure, which started at 11 a.m. and is necessary for the reconstruction and replacement of a box culvert structure and multiple pipe culverts.
The work zone is located approximately 14 miles east of Custer or nine miles west of the S.D. Highway 79 intersection. Highway 16A is closed between the intersection of Highway 16A/Iron Mountain Road and Custer State Park’s Wildlife Loop. This full closure is scheduled to remain in effect until April 2026.
Beyond the culvert replacement, the overall project includes replacing multiple pipe culverts, building gabion walls, and a mill and overlay of asphalt for 13 miles from Custer State Park’s east entrance to the west entrance. The entire project is slated for completion in October 2026.
Motorists are advised that a detour is in place. The route begins at the intersection of S.D. Highway 36 and Custer County’s Ritterberger Road, heads south two miles to Cobb Road, west one mile on Cobb Road, south one and one-half miles on Cobb Road to LH Road, west approximately two miles on LH Road to Custer State Park’s Wildlife Loop Road, and finally north two miles on the Wildlife Loop Road back to Highway 16A.
Travelers should note that six miles of the detour – on Ritterberger Road, Cobb Road, and LH Road – is gravel. The two miles on the Wildlife Loop Road is asphalt with a reduced speed limit of 25 mph. S.D. Highway 40 between Hermosa and Keystone also remains an alternate detour option for area motorists.
Custer State Park’s Wildlife Loop and Iron Mountain Road will remain open throughout the project duration.
Additional project information, including updates, photos, and a downloadable map of the detour, is available at https://dot.sd.gov/16a-culverts. The reconstruction is part of continued infrastructure improvements in western South Dakota.