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 Timeline:

Early Sept. 2025 - Fall of 2026

• The overall completion date is Oct. 30, 2026.
• No construction from Sept. 23, 2025, to Sept. 28, 2025, during Custer State Park’s Buffalo Roundup.
• Closure with detour will be in affect from Monday, Oct. 6, 2025, through Friday, April 3, 2026.
  
  
• No work:
  • Sturgis Rally
    - July 26, 2025 to Aug. 10, 2025
    - Aug. 1, 2025 to Aug. 17, 2026
  • Buffalo Roundup
    - Sept. 23 to Sept. 28, 2025
    - Sept. 22 to Sept. 27, 2026

Project Detour Map: 

Project Updates:

Jan. 7, 2026:

Beginning Monday, Jan. 12, 2026, reconstruction work is scheduled to begin on the realignment of Wildlife Loop Road in Custer State Park. This phase of the project includes a 600-foot section of U.S. Highway 16A at the intersection of Wildlife Loop Road and U.S. Highway 16A.

Crews will also construct two box culvert diversions located approximately three miles west of the U.S. Highway 16A and Wildlife Loop Road intersection.

Motorists should expect traffic delays of up to five minutes through the area during daytime operations. Flaggers will be present at both culvert locations to guide traffic through the work zones during daytime hours. During evening and overnight hours, two-way traffic will be maintained. Flaggers will remain on-site during working hours for the duration of the project. Additional delays are expected when paving begins in May.

Motorists are reminded to use caution and reduce speeds while workers and equipment are present.

Detour Routes:

As a reminder, Highway 16A will remain closed from the intersections of Highway 16A/Iron Mountain Road to Custer State Park’s Wildlife Loop. This closure will be in place until April 2026. During the Highway 16A closure, there will be a detour in place. The detour route is from the intersection of S.D. Highway 36 and Custer County’s Ritterberger Road, south two miles to Cobb Road intersection, west one mile on Cobb Road, south one and one-half miles on Cobb Road to the intersection of LH Road, west approximately two miles on LH Road to Custer State Park’s Wildlife Loop Road, and then north two miles on the Wildlife Loop Road back to Highway 16A. Motorists should be aware that the detour on Ritterberger Road, Cobb Road, and LH Road includes six miles of gravel. The Wildlife Loop Road is two miles of asphalt with a reduced speed limit of 25 mph. The South Dakota Department of Transportation (SDDOT) will perform winter maintenance/snow removal on the detour route.

S.D. Highway 40 between Hermosa and Keystone also provides a detour option for area motorists.

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Jan. 6, 2026: 

Anticipated Work: Jan. 5–Jan. 15, 2026:
Within the two-mile closure, the contractor will continue placing the box culvert’s base slab and wall forms, rebar and concrete.
Outside the closure, work will begin on realigning 600 feet of Custer State Park’s Wildlife Loop Road. Construction will also start on the first of four gabion walls and two road diversions for new box culverts. Flaggers will be used during this work, with expected delays of five minutes or less.

Nov. 15, 2025–Jan. 4, 2026 — Completed Work:
A two-mile closure of U.S. Highway 16A is in place from the intersection of Highway 16A/Iron Mountain Road to Custer State Park’s Wildlife Loop and will remain until April 2026. Custer State Park and Iron Mountain Road are open.
Within the closure, excavation of the existing box culvert for a new box culvert, along with installation of new pipe culverts and gabion baskets, has been completed. Just before Christmas, the first concrete for the box culvert’s base slab was placed.
The project will continue through winter, and the two-mile closure will remain in effect until early April 2026. The final completion date is Oct. 30, 2026.
The detour route begins at the intersection of S.D. Highway 36 and Custer County’s Ritterberger Road, then runs:

South two miles to the Cobb Road intersection
West one mile on Cobb Road
South 1.5 miles on Cobb Road to LH Road
West about two miles on LH Road to Custer State Park’s Wildlife Loop Road
North two miles on Wildlife Loop Road back to Highway 16A

Motorists should note that Ritterberger Road, Cobb Road and LH Road include six miles of gravel. Wildlife Loop Road is two miles of asphalt with a reduced speed limit of 25 mph.

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Sept. 12, 2025: 

Beginning at 11 a.m. MT on Monday, Oct. 6, 2025, a road construction project is scheduled to begin on U.S. Highway 16A near Custer. The reconstruction project to replace a box culvert structure and multiple pipe culverts is located 14 miles east of Custer or nine miles west of the S.D. Highway 79 intersection. 

Highway 16A will be closed from the intersections of Highway 16A/Iron Mountain Road to Custer State Park’s Wildlife Loop. This closure will be in place until April 2026. Additional work will include replacing multiple pipe culverts, building gabion walls, and mill and overlay asphalt from Custer State Park’s east entrance to the west entrance for 13 miles. Custer State Park’s Wildlife Loop and Iron Mountain Road will remain open throughout the project.

During the Highway 16A closure, there will be a detour in place. The detour route is from the intersection of S.D. Highway 36 and Custer County’s Ritterberger Road, south two miles to Cobb Road intersection, west one mile on Cobb Road, south one and one-half miles on Cobb Road to the intersection of LH Road, west approximately two miles on LH Road to Custer State Park’s Wildlife Loop Road, and then north two miles on the Wildlife Loop Road back to Highway 16A. Motorists should be aware that the detour on Ritterberger Road, Cobb Road, and LH Road includes six miles of gravel. The Wildlife Loop Road is two miles of asphalt with a reduced speed limit of 25 mph.

S.D. Highway 40 between Hermosa and Keystone also provides a detour option for area motorists.

Additional Project Information:
There will not be any active road construction work happening during the timeframe of Sept. 22 - 28, 2025, for the Custer State Park’s Buffalo Roundup event.

The prime contractor of this $15.6 million project is Paul Reed Construction & Supply, Inc. of Gering, NE. The overall project completion date is October 2026.

Project Photos:

Project Contract Amount: