Home › South Dakota › Union County › SD46 over Big Sioux River

SD46 over Big Sioux River

Union County, South Dakota · rated Fair in the 2025 National Bridge Inventory

United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled August 20, 2026

SD46 over Big Sioux River in Union County, South Dakota, is rated in fair condition in the 2025 National Bridge Inventory (as of August 20, 2026).
Its lowest-rated component is the deck, rated 6 (satisfactory condition) on the 0-9 scale.
It was built in 1991, making it 34 years old at the 2025 inventory.
It carries about 1,610 vehicles a day (traffic count year 2023).
Its listed owner is the state highway agency.
It is one of 77 of the 169 inventoried bridges in Union County rated fair (45.6%); 41 (24.3%) are rated poor.
A fair rating means the lowest-rated major component scores 5 or 6 on FHWA's 0-9 scale: some deterioration or minor section loss, but the structure is sound. It is the middle class, not a warning.

Component ratings


Structure	Prestressed concrete stringer or multi-beam girder
Length	about 518 ft
Location	at South Dakota Border
NBI structure number	000000064160023
Condition class	Fair

Source: FHWA National Bridge Inventory, 2025 data as reported by the South Dakota department of transportation.

Bridge	Built	Vehicles/day	Condition
I029 S over Big Sioux Rv	1990	18,090	Good
I029 N over Big Sioux Rv	1963	18,090	Fair
I029 over Ck	1961	11,970	Good
I029 over Ck	1961	11,970	Good
I029 over Ck	1961	11,970	Good
I029 S over River Drive	1981	9,870	Good