County profile · official public datasets

Brown County, SD

170 public highway bridges tracked in the FHWA National Bridge Inventory: 32.9% rated Good, 55.3% Fair, 11.8% Poor.

170
Public bridges: 32.9%
Good condition: 11.8%
Poor condition

The verdict

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

Brown County pairs a better-than-median Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

Top 38%
lowest Poor share in state: 11.8%
Poor-condition share: 170
public highway bridges: 1983
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.

Brown County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Brown County ranks #25 of 66 South Dakota counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 11.8%). Brown County, South Dakota contains 170 public highway bridges. Roughly 32.9% are rated “Good,” 55.3% “Fair,” and 11.8% “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 Brown County

Good condition

32.9%

56 of 170 rated 7-9

Fair condition

55.3%

94 of 170 rated 5-6

Poor condition

11.8%

20 of 170 rated 4 or below

In-state Poor-share rank

#25 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

32.9% (56)

Fair

55.3% (94)

Poor

11.8% (20)

Brown County's Poor-condition bridges carry 27,890 vehicle crossings a day

That is 18.7% of the county's reported daily bridge traffic on 11.8% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 1,395 crossings a day against 446 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 170 of 170 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

36.5% of Brown County's bridges have passed the 50-year mark

62 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 32.9% 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 80.1% of the county's Poor-condition bridge traffic

US012 over MOCCASIN CK, built 1954, carries 22,327 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 20-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 27,890 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

1
1910s

1
1920s

4
1930s

16
1940s

4
1950s

14
1960s

6
1970s

23
1980s

16
1990s

18
2000s

33
2010s

28
2020s

6

What this shows Construction peaked in the 2000s, when 33 of the county's bridges still in the inventory were built, which is 19.4% of those with a recorded year. That cohort is now 15 to 24 years old in the 2024 inventory. Its average build year is 1983, 8 years newer than the South Dakota average of 1975.

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

The 5 South Dakota counties nearest Brown County in number of bridges, with their condition splits. Its 11.8% Poor share is the 1st-lowest of these 6. Its average build year of 1983 against a peer-group mean of 1966 is 17 years newer.

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

Bridge inventory size and condition shares for Brown 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
Union County	170	31.2%	49.4%	19.4%	1975
Brown County (this page)	170	32.9%	55.3%	11.8%	1983
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 Brown 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 Brown 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 (1983 here).

Dallas County, TX · avg 1983 · 3,230 bridges
Bexar County, TX · avg 1983 · 2,342 bridges
Sedgwick County, KS · avg 1983 · 1,333 bridges
Will County, IL · avg 1983 · 649 bridges

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

All 170 Good 56 Fair 94 Poor 20

Fair-condition bridges (94)

Sort:

Brown County Bridge Snapshot

Condition distribution

Brown County's Poor-condition bridges carry 27,890 vehicle crossings a day

36.5% of Brown County's bridges have passed the 50-year mark

One structure carries 80.1% of the county's Poor-condition bridge traffic

How Brown 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

Fair-condition bridges (94)

147th Street

US012 W

SD037

110th Street

SECOND STREET

SD037

US281

144th Street

SD037

SECOND STREET

SECOND STREET

SD037

137th Street

US012

382nd Avenue

US012 W

140th Street

139th Street

405th Avenue

SD037

US281

396th Avenue

117th Street

111th Street

US012

US281 S

US281 N

395th Avenue

133rd Street

US012 E

US281 S

US281 N

142nd Street

US012

141st Street

US012 E

US012 W

US012 E

146th Street

US281

126th Street

404th Avenue

144th Street

101st Street

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