County profile · official public datasets

Mahaska County, IA

225 public highway bridges tracked in the FHWA National Bridge Inventory: 28.4% rated Good, 39.1% Fair, 32.4% Poor.

225
Public bridges: 28.4%
Good condition: 32.4%
Poor condition

The verdict

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

Mahaska County pairs a higher-than-median Poor-condition share among rated counties in the state with an older average build year than the state inventory.

85th
of 99 on Poor share: 32.4%
Poor-condition share: 225
public highway bridges: 1972
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.

Mahaska County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Mahaska County ranks #85 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 32.4%). Mahaska County, Iowa contains 225 public highway bridges. Roughly 28.4% are rated “Good,” 39.1% “Fair,” and 32.4% “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

225

Public highway bridges in Mahaska County

Good condition

28.4%

64 of 225 rated 7-9

Fair condition

39.1%

88 of 225 rated 5-6

Poor condition

32.4%

73 of 225 rated 4 or below

In-state Poor-share rank

#85 of 99

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

Condition distribution

Share of 225 NBI-tracked bridges by lowest applicable component rating.

Good

28.4% (64)

Fair

39.1% (88)

Poor

32.4% (73)

Mahaska County's Poor-condition bridges carry 10,792 vehicle crossings a day

That is 6.2% of the county's reported daily bridge traffic on 32.6% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 148 crossings a day against 1,231 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 224 of 225 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

58.7% of Mahaska County's bridges have passed the 50-year mark

132 of the 225 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 28.4% 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 21.8% of the county's Poor-condition bridge traffic

IA 23 over TRIBUTARY OF CEDAR CREEK, built 1928, carries 2,350 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 73-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 10,792 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

6
1920s

3
1930s

1
1940s

8
1950s

66
1960s

30
1970s

25
1980s

22
1990s

34
2000s

16
2010s

9
2020s

5

What this shows Construction peaked in the 1950s, when 66 of the county's bridges still in the inventory were built, which is 29.3% of those with a recorded year. That cohort is now 65 to 74 years old in the 2024 inventory. Its average build year is 1972, 7 years older than the Iowa average of 1979.

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

The 5 Iowa counties nearest Mahaska County in number of bridges, with their condition splits. Its 32.4% Poor share is the 3rd-lowest of these 6. Its average build year of 1972 against a peer-group mean of 1975 is in line with the group.

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

Bridge inventory size and condition shares for Mahaska County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Jones County	231	36.8%	58.9%	4.3%	1981
Franklin County	228	44.7%	42.1%	13.2%	1982
Madison County	225	16%	46.7%	37.3%	1968
Mahaska County (this page)	225	28.4%	39.1%	32.4%	1972
Sac County	224	35.7%	30.8%	33.5%	1973
Taylor County	220	24.5%	37.7%	37.7%	1973

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

Similar inventory size

Nearest county inventories outside IA (225 bridges here).

Dallas County, AL · 225 bridges
Lincoln County, KS · 225 bridges
Lenawee County, MI · 225 bridges
Clay County, MN · 225 bridges

Similar average build year

Nearest mean year-built outside IA (1972 here).

Santa Clara County, CA · avg 1972 · 964 bridges
Madison County, AL · avg 1972 · 710 bridges
Kern County, CA · avg 1972 · 668 bridges
York County, PA · avg 1972 · 569 bridges

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

All 225 Good 64 Fair 88 Poor 73

Fair-condition bridges (88)

Sort:

Mahaska County Bridge Snapshot

Condition distribution

Mahaska County's Poor-condition bridges carry 10,792 vehicle crossings a day

58.7% of Mahaska County's bridges have passed the 50-year mark

One structure carries 21.8% of the county's Poor-condition bridge traffic

How Mahaska 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 (88)

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OLD IA 102

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