County profile · official public datasets

Union County, SD

170 public highway bridges tracked in the FHWA National Bridge Inventory: 31.2% rated Good, 49.4% Fair, 19.4% Poor.

170
Public bridges: 31.2%
Good condition: 19.4%
Poor condition

The verdict

According to the Federal Highway Administration's 2024 National Bridge Inventory.

Union County posts a higher-than-median Poor-condition share among rated counties in the state across mid-size county bridge inventory.

45th
of 66 on Poor share: 19.4%
Poor-condition share: 170
public highway bridges: 1975
avg year built

Poor is an FHWA condition category from the lowest applicable component rating (4 or below), not a live crossing-safety or closure decision. Rankings cover counties with at least five public highway bridges.

Union County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Union County ranks #45 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 19.4%). Union County, South Dakota contains 170 public highway bridges. Roughly 31.2% are rated “Good,” 49.4% “Fair,” and 19.4% “Poor.” Poor means the lowest applicable deck, superstructure, substructure, or culvert rating is 4 or below on the 0–9 NBI scale. It is a condition category, not a live safety or closure decision.

Responsible agencies inspect covered bridges on risk-based intervals under current NBIS rules and submit inventory data to FHWA annually. The list below shows every NBI-tracked bridge in the county. Use the “Sort by” controls to change the ordering, and click any row for its reported inspection date, traffic count, and condition fields.

Source: FHWA National Bridge Inventory. See methodology for full definitions.

Total bridges

170

Public highway bridges in Union County

Good condition

31.2%

53 of 170 rated 7-9

Fair condition

49.4%

84 of 170 rated 5-6

Poor condition

19.4%

33 of 170 rated 4 or below

In-state Poor-share rank

#45 of 66

Among South Dakota counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 170 NBI-tracked bridges by lowest applicable component rating.

Good

31.2% (53)

Fair

49.4% (84)

Poor

19.4% (33)

Union County's Poor-condition bridges carry 10,448 vehicle crossings a day

That is 4.9% of the county's reported daily bridge traffic on 19.5% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 317 crossings a day against 1,917 for a Good-condition one. A Poor rating is a condition category, not a closure or a live safety judgement; it means the lowest applicable component rating is 4 or below.

Computed over the 169 of 170 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

49.4% of Union County's bridges have passed the 50-year mark

84 of the 170 bridges with a recorded construction year were built in 1974 or earlier. Age alone is not a defect: a well-maintained older bridge can rate Good, and 31.2% of this county's inventory does. Even so, this older cohort is the population from which future Poor ratings are drawn, which is why the age profile below matters alongside the condition split above.

Cutoff derives from the 2024 release year minus a 50-year design life. Source: FHWA National Bridge Inventory, 2024 release.

One structure carries 74.5% of the county's Poor-condition bridge traffic

I029 N over 302 ST (FAS 6372), built 1960, carries 7,780 vehicles a day, the most of any Poor-rated structure here. The county's Poor-condition exposure is concentrated rather than evenly spread, so the 33-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 10,448 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1930s

5
1940s

12
1950s

20
1960s

43
1970s

14
1980s

31
1990s

17
2000s

13
2010s

8
2020s

7

What this shows Construction peaked in the 1960s, when 43 of the county's bridges still in the inventory were built, which is 25.3% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1975) matches the South Dakota average (1975).

How Union County compares with South Dakota's closest counties by inventory size

The 5 South Dakota counties nearest Union County in number of bridges, with their condition splits. Its 19.4% Poor share is the 3rd-lowest of these 6. Its average build year of 1975 against a peer-group mean of 1968 is 7 years newer.

Showing the 5 closest of 65 South Dakota counties eligible for comparison.

Bridge inventory size and condition shares for Union County and the 5 South Dakota counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Spink County	176	13.6%	52.8%	33.5%	1957
Brown County	170	32.9%	55.3%	11.8%	1983
Union County (this page)	170	31.2%	49.4%	19.4%	1975
Hutchinson County	161	32.9%	50.9%	16.1%	1974
Roberts County	157	22.9%	52.9%	24.2%	1970
Beadle County	152	19.1%	47.4%	33.6%	1955

Each share is of that county's own total tracked bridges; peers are the counties with 5 or more bridges whose inventory size is closest to Union County's. Source: FHWA National Bridge Inventory, 2024 release.

Nationwide counties with similar inventory size or average build year

Two NBI-derived peer sets for Union County, both outside South Dakota so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside SD (170 bridges here).

Rush County, KS · 170 bridges
Itasca County, MN · 170 bridges
Montgomery County, MS · 170 bridges
Clarendon County, SC · 170 bridges

Similar average build year

Nearest mean year-built outside SD (1975 here).

San Bernardino County, CA · avg 1975 · 1,422 bridges
Lane County, OR · avg 1975 · 1,010 bridges
Fulton County, GA · avg 1975 · 775 bridges
Westmoreland County, PA · avg 1975 · 620 bridges

Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.

All 170 Good 53 Fair 84 Poor 33

All bridges (170)

Sort:

Union County Bridge Snapshot

Condition distribution

Union County's Poor-condition bridges carry 10,448 vehicle crossings a day

49.4% of Union County's bridges have passed the 50-year mark

One structure carries 74.5% of the county's Poor-condition bridge traffic

How Union County compares with South Dakota's closest counties by inventory size

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

All bridges (170)

472 AVE

475 AVE

300 ST

SD048

30070 474TH AVE

SD048

SD048 EF

48580 COUNTY RD 13

I029 S

I029 N

306 ST (FAS 6370)

298 ST

31080 473 AVE.

SD011

SD46

I029 N

SD048

47690 305 STR.

SD050

SD029 P

SD048

SD011

SD048

48480 298TH ST

47659 320 ST.

DAKOTA DUNES BLVD

SD048

47260 311 ST

48060 306 STR.

47110 309 STR.

I029 S

48080 308 STR.

31180 476TH AVE

SD046

47860 307TH ST

31870 477TH AVE

31450 471 AVE.

31410 474TH AVE

31260 475TH AVE

30940 476TH AVE

31590 476 TH AVE

32050 478TH AVE

SD050

47690 310TH ST

47610 316 ST

48340 301ST

31160 474TH AVE

47190 307 ST.

47180 311TH STREET

30890 471 AVE.

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