County profile · official public datasets

Humboldt County, IA

87 public highway bridges tracked in the FHWA National Bridge Inventory: 36.8% rated Good, 52.9% Fair, 10.3% Poor.

87
Public bridges: 36.8%
Good condition: 10.3%
Poor condition

The verdict

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

Humboldt County pairs a top-quartile lowest Poor-condition share among rated counties in the state with an older average build year than the state inventory.

Top 23%
lowest Poor share in state: 10.3%
Poor-condition share: 87
public highway bridges: 1965
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.

Humboldt County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Humboldt County ranks #23 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 10.3%). Humboldt County, Iowa contains 87 public highway bridges. Roughly 36.8% are rated “Good,” 52.9% “Fair,” and 10.3% “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

Public highway bridges in Humboldt County

Good condition

36.8%

32 of 87 rated 7-9

Fair condition

52.9%

46 of 87 rated 5-6

Poor condition

10.3%

9 of 87 rated 4 or below

In-state Poor-share rank

#23 of 99

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

Condition distribution

Share of 87 NBI-tracked bridges by lowest applicable component rating.

Good

36.8% (32)

Fair

52.9% (46)

Poor

10.3% (9)

Humboldt County's Poor-condition bridges carry 383 vehicle crossings a day

That is 0.6% of the county's reported daily bridge traffic on 10.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 43 crossings a day against 813 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 87 of 87 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

56.3% of Humboldt County's bridges have passed the 50-year mark

49 of the 87 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 36.8% 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 47% of the county's Poor-condition bridge traffic

LOCAL over CREEK, built 1900, carries 180 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 9-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 383 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

pre-1900

1
1900s

14
1910s

2
1920s

1
1930s

4
1940s

5
1950s

13
1960s

5
1970s

5
1980s

8
1990s

7
2000s

10
2010s

11
2020s

1

What this shows Construction peaked in the 1900s, when 14 of the county's bridges still in the inventory were built, which is 16.1% of those with a recorded year. That cohort is now 115 to 124 years old in the 2024 inventory. Its average build year is 1965, 14 years older than the Iowa average of 1979.

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

The 5 Iowa counties nearest Humboldt County in number of bridges, with their condition splits. Its 10.3% Poor share is the 1st-lowest of these 6. Its average build year of 1965 against a peer-group mean of 1977 is 12 years older.

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

Bridge inventory size and condition shares for Humboldt County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Monroe County	130	26.2%	49.2%	24.6%	1977
Worth County	116	35.3%	48.3%	16.4%	1970
Humboldt County (this page)	87	36.8%	52.9%	10.3%	1965
Dickinson County	84	40.5%	41.7%	17.9%	1981
Emmet County	78	23.1%	60.3%	16.7%	1973
Winnebago County	55	30.9%	36.4%	32.7%	1984

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

Similar inventory size

Nearest county inventories outside IA (87 bridges here).

Modoc County, CA · 87 bridges
Hendry County, FL · 87 bridges
Adams County, ID · 87 bridges
Rockcastle County, KY · 87 bridges

Similar average build year

Nearest mean year-built outside IA (1965 here).

Windsor County, VT · avg 1965 · 483 bridges
Bedford County, PA · avg 1965 · 417 bridges
Crawford County, PA · avg 1965 · 399 bridges
Harper County, KS · avg 1965 · 372 bridges

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

All 87 Good 32 Fair 46 Poor 9

All bridges (87)

Sort:

Humboldt County Bridge Snapshot

Condition distribution

Humboldt County's Poor-condition bridges carry 383 vehicle crossings a day

56.3% of Humboldt County's bridges have passed the 50-year mark

One structure carries 47% of the county's Poor-condition bridge traffic

How Humboldt 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

All bridges (87)

IA 15

FM

SUMNER AVE SW

US 169

FM

KANSAS AVE

JUNIPER AVE

270TH ST

IA 3

GEORGIA AVE

FM

C20 130TH ST

VIRGINIA AVE

LOCAL

MONTANA AVE

LOCAL

LOCAL

FM

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

JUNIPER AVE

FM

FM

US 169

FM

LOCAL

215TH ST

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

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