Bridge conditions in Union County, South Dakota

169 inventoried bridges · 41 rated poor · 2025 National Bridge Inventory

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

Union County has 41 bridges rated poor out of 169 inventoried, a 24.3% share that puts it well above the national rate of about 7%.

41 of the 169 bridges in Union County, South Dakota, are rated in poor condition (24.3%) in the 2025 National Bridge Inventory, as of August 20, 2026.
51 bridges (30.2%) are rated good and 77 (45.6%) fair.
The median Union County bridge was built in 1977.
The busiest poor-rated bridge is I029 N over 302 St (fas 6372) (built 1960), carrying about 8,020 vehicles a day.

Good 30.2% · Fair 45.6% · Poor 24.3% of 169 bridges

Bridges rated poor

Every bridge in the county with a poor rating, busiest first. Poor means a major component is rated 4 or lower on FHWA's 0-9 scale; it is a repair flag, not a closure notice.

Bridge	Built	Vehicles/day	Condition
I029 N over 302 St (fas 6372)	1960	8,020	Poor
48480 Co Hwy 13 over Green Ck	1985	500	Poor
47400 302 St. over West Brule Ck	1960	435	Poor
30330 River Road over Ck	1972	325	Poor
30999 477TH Ave over Ck	1989	300	Poor
31490 477TH Ave over Br Brule Ck	1955	300	Poor
47580 302ND St over East Brule Ck	1960	270	Poor
48050 311TH St over East Union Ck	1950	110	Poor
29895 Boyer Ave over Ck	1992	70	Poor
31490 475TH St over Brule Ck	1977	60	Poor
48480 298TH St over Ck	1987	55	Poor
47610 312TH St over Ck	1992	50	Poor
47230 305 Str. over Ck	1987	45	Poor
30010 478 Ave. over Ck	1982	45	Poor
30040 478 Ave. over Drainage Ditch	1983	45	Poor
47880 306 Str. over Ck	1950	45	Poor
48020 309 Str. over East Union Ck	1950	45	Poor
48140 312TH St over Ck	1940	45	Poor
30320 482ND Ave over Ck	1983	45	Poor
30310 483RD Ave over Ck	1983	45	Poor
47320 304 Str over Ck	1970	43	Poor
47320 305 Str over Brule Ck	1989	40	Poor
30070 474TH Ave over West Brule Ck	1982	40	Poor
47460 304 Str. over Brule Ck	1987	40	Poor
32200 477TH Ave over Lewis Ditch	1968	40	Poor
32201 478TH Ave. over Lewis Ditch	1940	40	Poor
47960 312TH St over West Union Ck	1986	40	Poor
30820 480 Ave. over Ck	1935	40	Poor
48030 310 Str. over East Union Ck	1948	40	Poor
47160 310 Str. over Brule Ck	1970	35	Poor
31128 472ND Ave.rd over Brule Ck	1985	35	Poor
47230 306 Str. over Brule Ck	1979	35	Poor
47340 306 Str. over Ck	1948	35	Poor
31070 476TH Ave over Ck	1963	35	Poor
47700 300 Str. over Ck	1982	35	Poor
30330 472 Ave. over Ck	1973	30	Poor
47570 311 Str. over Ck	1955	30	Poor
47340 310TH St over Ck	1935	25	Poor
30600 476 Ave. over Ck	1965	25	Poor
48040 312TH St over East Union Ck	1950	25	Poor
29730 484TH Ave over Ck	1983	25	Poor

Busiest bridges in the county

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
I029 N over River Drive	1981	9,870	Good
I029 S over 302 St (fas 6372)	1960	8,020	Fair
I029 N over 302 St (fas 6372)	1960	8,020	Poor
I029 S over Ck	1961	7,770	Fair

Source: FHWA National Bridge Inventory, 2025. Counts cover inventoried highway bridges over 20 feet; ratings are reported by the state DOT.

Every bridge in Union County → - all 169, busiest first, each with its own condition record.

All of South Dakota: South Dakota bridge conditions by county · every download on the data page.

Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.