County profile · official public datasets

Sioux County, IA

449 public highway bridges tracked in the FHWA National Bridge Inventory: 62.4% rated Good, 34.7% Fair, 2.9% Poor.

449
Public bridges: 62.4%
Good condition: 2.9%
Poor condition

The verdict

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

Sioux County posts a top-1% lowest Poor-condition share among rated counties in the state across mid-size county bridge inventory.

Top 1%
lowest Poor share in state: 2.9%
Poor-condition share: 449
public highway bridges: 1982
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.

Sioux County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Sioux County ranks #1 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 2.9%). Sioux County, Iowa contains 449 public highway bridges. Roughly 62.4% are rated “Good,” 34.7% “Fair,” and 2.9% “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

449

Public highway bridges in Sioux County

Good condition

62.4%

280 of 449 rated 7-9

Fair condition

34.7%

156 of 449 rated 5-6

Poor condition

2.9%

13 of 449 rated 4 or below

In-state Poor-share rank

#1 of 99

Among Iowa counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 449 NBI-tracked bridges by lowest applicable component rating.

Good

62.4% (280)

Fair

34.7% (156)

Poor

2.9% (13)

Sioux County's Poor-condition bridges carry 4,979 vehicle crossings a day

That is 1.9% of the county's reported daily bridge traffic on 2.9% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 383 crossings a day against 550 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 449 of 449 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

32.1% of Sioux County's bridges have passed the 50-year mark

144 of the 449 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 62.4% 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 20.4% of the county's Poor-condition bridge traffic

FM over ROCK RIVER, built 1952, carries 1,017 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 13-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 4,979 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

6
1930s

28
1940s

14
1950s

16
1960s

60
1970s

73
1980s

67
1990s

66
2000s

73
2010s

40
2020s

6

What this shows Construction peaked in the 1970s, when 73 of the county's bridges still in the inventory were built, which is 16.3% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year (1982) matches the Iowa average (1979).

How Sioux County compares with Iowa's closest counties by inventory size

The 5 Iowa counties nearest Sioux County in number of bridges, with their condition splits. Its 2.9% Poor share is the 1st-lowest of these 6. Its average build year of 1982 against a peer-group mean of 1981 is in line with the group.

Showing the 5 closest of 98 Iowa counties eligible for comparison.

Bridge inventory size and condition shares for Sioux County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Linn County	506	46.4%	47.2%	6.3%	1987
Black Hawk County	489	52.8%	40.7%	6.5%	1983
Woodbury County	455	39.3%	39.6%	21.1%	1985
Sioux County (this page)	449	62.4%	34.7%	2.9%	1982
Plymouth County	432	52.1%	26.4%	21.5%	1974
Jasper County	382	38.5%	32.5%	29.1%	1977

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 Sioux 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 Sioux County, both outside Iowa so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside IA (449 bridges here).

Washington County, AR · 449 bridges
Barton County, KS · 449 bridges
Grady County, OK · 449 bridges
Dauphin County, PA · 449 bridges

Similar average build year

Nearest mean year-built outside IA (1982 here).

Oklahoma County, OK · avg 1982 · 1,216 bridges
Jackson County, MO · avg 1982 · 930 bridges
Milwaukee County, WI · avg 1982 · 893 bridges
Champaign County, IL · avg 1982 · 727 bridges

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

All 449 Good 280 Fair 156 Poor 13

Fair-condition bridges (156)

Sort:

Sioux County Bridge Snapshot

Condition distribution

Sioux County's Poor-condition bridges carry 4,979 vehicle crossings a day

32.1% of Sioux County's bridges have passed the 50-year mark

One structure carries 20.4% of the county's Poor-condition bridge traffic

How Sioux County compares with Iowa'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 (156)

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