County profile · official public datasets

Marshall County, IA

304 public highway bridges tracked in the FHWA National Bridge Inventory: 32.9% rated Good, 23.7% Fair, 43.4% Poor.

304
Public bridges: 32.9%
Good condition: 43.4%
Poor condition

The verdict

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

Marshall 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.

98th
of 99 on Poor share: 43.4%
Poor-condition share: 304
public highway bridges: 1970
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.

Marshall County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Marshall County ranks #98 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 43.4%). Marshall County, Iowa contains 304 public highway bridges. Roughly 32.9% are rated “Good,” 23.7% “Fair,” and 43.4% “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

304

Public highway bridges in Marshall County

Good condition

32.9%

100 of 304 rated 7-9

Fair condition

23.7%

72 of 304 rated 5-6

Poor condition

43.4%

132 of 304 rated 4 or below

In-state Poor-share rank

#98 of 99

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

Condition distribution

Share of 304 NBI-tracked bridges by lowest applicable component rating.

Good

32.9% (100)

Fair

23.7% (72)

Poor

43.4% (132)

Marshall County's Poor-condition bridges carry 47,789 vehicle crossings a day

That is 13.6% of the county's reported daily bridge traffic on 43.6% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 362 crossings a day against 1,912 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 303 of 304 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

48.4% of Marshall County's bridges have passed the 50-year mark

147 of the 304 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 21.9% of the county's Poor-condition bridge traffic

SO CENTER ST over LINN CREEK, built 1951, carries 10,448 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 132-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 47,789 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

1
1910s

33
1920s

6
1930s

15
1940s

30
1950s

36
1960s

17
1970s

27
1980s

46
1990s

28
2000s

42
2010s

15
2020s

8

What this shows Construction peaked in the 1980s, when 46 of the county's bridges still in the inventory were built, which is 15.1% of those with a recorded year. That cohort is now 35 to 44 years old in the 2024 inventory. Its average build year is 1970, 9 years older than the Iowa average of 1979.

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

The 5 Iowa counties nearest Marshall County in number of bridges, with their condition splits. Its 43.4% Poor share is the 6th-lowest of these 6. Its average build year of 1970 against a peer-group mean of 1980 is 10 years older.

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

Bridge inventory size and condition shares for Marshall County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Adair County	306	46.7%	39.9%	13.4%	1983
Marshall County (this page)	304	32.9%	23.7%	43.4%	1970
Chickasaw County	302	42.1%	30.1%	27.8%	1986
Cedar County	301	42.9%	37.5%	19.6%	1983
Crawford County	301	42.5%	48.5%	9%	1982
Story County	296	33.1%	53%	13.9%	1968

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

Similar inventory size

Nearest county inventories outside IA (304 bridges here).

Coles County, IL · 304 bridges
Knox County, IL · 304 bridges
Osage County, KS · 304 bridges
Nobles County, MN · 304 bridges

Similar average build year

Nearest mean year-built outside IA (1970 here).

Hamilton County, OH · avg 1970 · 783 bridges
Yavapai County, AZ · avg 1970 · 543 bridges
Garfield County, OK · avg 1970 · 504 bridges
San Luis Obispo County, CA · avg 1970 · 401 bridges

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

All 304 Good 100 Fair 72 Poor 132

All bridges (304)

Sort:

Marshall County Bridge Snapshot

Condition distribution

Marshall County's Poor-condition bridges carry 47,789 vehicle crossings a day

48.4% of Marshall County's bridges have passed the 50-year mark

One structure carries 21.9% of the county's Poor-condition bridge traffic

How Marshall 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 (304)

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