The major byway between Pierre and Sturgis is closing for about five weeks, so the state's urging drivers to avoid the 76-mile detour.
The Department of Transportation says the 2 1/2 mile stretch of Highway 34 east of Howes will be closed on Monday just east of the Highway 73 North junction.
A contractor has to repair erosion from heavy rains on dams for Howes Lake and Lake Buffalo.
While the road is closed, travelers from the east are being detoured north on Highway 63 to Highway 212, then west on Highway 212 to Highway 73 at Faith and south on Highway 73 back to Highway 34. Travelers from the west will be detoured north on 73, east on 212 and south on 63 back to Highway 34.