County profile · official public datasets

Decatur County, IA

197 public highway bridges tracked in the FHWA National Bridge Inventory: 18.3% rated Good, 41.1% Fair, 40.6% Poor.

197
Public bridges: 18.3%
Good condition: 40.6%
Poor condition

The verdict

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

Decatur 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.

95th
of 99 on Poor share: 40.6%
Poor-condition share: 197
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.

Decatur County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Decatur County ranks #95 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 40.6%). Decatur County, Iowa contains 197 public highway bridges. Roughly 18.3% are rated “Good,” 41.1% “Fair,” and 40.6% “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

197

Public highway bridges in Decatur County

Good condition

18.3%

36 of 197 rated 7-9

Fair condition

41.1%

81 of 197 rated 5-6

Poor condition

40.6%

80 of 197 rated 4 or below

In-state Poor-share rank

#95 of 99

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

Condition distribution

Share of 197 NBI-tracked bridges by lowest applicable component rating.

Good

18.3% (36)

Fair

41.1% (81)

Poor

40.6% (80)

Decatur County's Poor-condition bridges carry 5,581 vehicle crossings a day

That is 4.6% of the county's reported daily bridge traffic on 40.6% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 70 crossings a day against 328 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 197 of 197 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

57.4% of Decatur County's bridges have passed the 50-year mark

113 of the 197 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 18.3% 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 10.9% of the county's Poor-condition bridge traffic

US 69 over ZADIE CREEK, built 1925, carries 610 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 80-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 5,581 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

3
1910s

4
1920s

10
1930s

4
1940s

3
1950s

34
1960s

38
1970s

25
1980s

22
1990s

20
2000s

19
2010s

15

What this shows Construction peaked in the 1960s, when 38 of the county's bridges still in the inventory were built, which is 19.3% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year is 1972, 7 years older than the Iowa average of 1979.

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

The 5 Iowa counties nearest Decatur County in number of bridges, with their condition splits. Its 40.6% Poor share is the 6th-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 Decatur County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Dallas County	199	44.7%	46.2%	9%	1978
Allamakee County	197	31.5%	59.4%	9.1%	1975
Calhoun County	197	24.4%	50.3%	25.4%	1971
Decatur County (this page)	197	18.3%	41.1%	40.6%	1972
Page County	196	24%	43.9%	32.1%	1975
Lucas County	195	32.3%	34.4%	33.3%	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 Decatur 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 Decatur County, both outside Iowa so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside IA (197 bridges here).

Crawford County, IL · 197 bridges
Fountain County, IN · 197 bridges
Warrick County, IN · 197 bridges
Atchison County, KS · 197 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 197 Good 36 Fair 81 Poor 80

Fair-condition bridges (81)

Sort:

Decatur County Bridge Snapshot

Condition distribution

Decatur County's Poor-condition bridges carry 5,581 vehicle crossings a day

57.4% of Decatur County's bridges have passed the 50-year mark

One structure carries 10.9% of the county's Poor-condition bridge traffic

How Decatur 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 (81)

LOCAL

LOCAL

LOCAL

LOCAL

FM

FM

LOCAL

FM

LOCAL

LOCAL

FM

LOCAL

FM

FM

LOCAL

LOCAL

FM

LOCAL

FM

290TH AVE

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

FM

FM

US 69 & IA 2

LOCAL

US 69

FM

LOCAL

US 69

FM

SB I-35

FM

LOCAL

FM J-20

IA 2

SB I-35

NB I-35

250TH STREET

J14

FIELD ENTRANCE

NB I-35

IA 2

IA 2

IA 2

LOCAL

NB I-35

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