U.S. Highway 16A - From two miles east of Custer to Jct. S.D. Highway 36
Project Summary:
The project consists of the replacement of various pipe culverts on U.S. Highway 16A that have exceeded their useful life. Additional work on the project includes removing and replacing existing asphalt surfacing, repairing in-slope erosion adjacent to the highway, and improving the intersection of U.S. Highway 16A and Wildlife Loop Road.
The project also consists of the replacement of a concrete arch culvert that has exceeded its useful life.
Project Updates:
March 31, 2026:
Beginning Friday, April 3, 2026, the two-mile closure on U.S. Highway 16A in Custer State Park will reopen to traffic. The six mile gravel detour will no longer be in use.
The two-mile closure is located approximately 14 miles east of Custer or nine miles west of the S.D. Highway 79 intersection. The detour was in place to allow for replacement of a box culvert structure and multiple pipe culverts, which have now been completed. Within the two-mile segment, approximately one-tenth of a mile will remain gravel until mid-May, when asphalt is scheduled to be placed.
Additional work on the project includes replacement of multiple pipe culverts, guardrail installation, and a 600-foot realignment of Wildlife Loop Road within Custer State Park. An asphalt mill and overlay will also take place along 13 miles of U.S. Highway 16A between the east and west entrances of Custer State Park. Asphalt work is scheduled to begin in May and will require the use of pilot cars and flaggers, with delays of up to 15 minutes.
March 18, 2026:
Anticipated Work March 16 – April 15, 2026:
Within the two-mile closure, crews will begin placing new curb and gutter east of the box culvert to improve drainage. Crews will also replace guardrail that was removed during construction.
The timber bridge rail located just west of Custer State Park’s east entrance will be replaced with new timber railing. The two-mile closure is anticipated to reopen to traffic on Friday, April 3, 2026, weather permitting.
Outside the closure, crews will continue construction of the 600-foot realignment of Custer State Park’s Wildlife Loop Road. Work will include installing two new twin box culverts and additional drainage culverts.
Flaggers and temporary traffic signals will be used at active work areas. Motorists should expect delays of five minutes or less when flaggers or signals are in operation.
Completed Work Jan. 23, 2025 – March 16, 2026:
A two-mile closure on U.S. Highway 16A remains in place from the intersection of U.S. Highway 16A and Iron Mountain Road to Custer State Park’s Wildlife Loop Road. The closure will remain in place until early April 2026. Custer State Park and Iron Mountain Road remain open.
Within the two-mile closure, construction of the new box culvert has been completed and backfill over the structure is finished.
Outside the closure, crews continued work on a 600-foot realignment of Custer State Park’s Wildlife Loop Road. Work included beginning excavation of the slopes. All four gabion retaining walls have been completed.
The project will continue through the winter and spring months. The two-mile road closure is expected to remain in place until early April 2026. The project’s final completion date is Oct. 30, 2026.
Detour Information:
Motorists traveling around the closure will be detoured from the intersection of S.D. Highway 36 and Ritterberger Road:
South two miles on Ritterberger Road to Cobb Road
West one mile on Cobb Road
South 1.5 miles on Cobb Road to LH Road
West approximately two miles on LH Road to Custer State Park’s Wildlife Loop Road
North two miles on Wildlife Loop Road back to U.S. Highway 16A
Motorists should be aware the detour includes approximately six miles of gravel on Ritterberger Road, Cobb Road and LH Road. Wildlife Loop Road is paved but has a reduced speed limit of 25 mph.