County profile · official public datasets

Carroll County, IA

249 public highway bridges tracked in the FHWA National Bridge Inventory: 48.6% rated Good, 44.6% Fair, 6.8% Poor.

249
Public bridges: 48.6%
Good condition: 6.8%
Poor condition

The verdict

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

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

Top 11%
lowest Poor share in state: 6.8%
Poor-condition share: 249
public highway bridges: 1977
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.

Carroll County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Carroll County ranks #11 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 6.8%). Carroll County, Iowa contains 249 public highway bridges. Roughly 48.6% are rated “Good,” 44.6% “Fair,” and 6.8% “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

249

Public highway bridges in Carroll County

Good condition

48.6%

121 of 249 rated 7-9

Fair condition

44.6%

111 of 249 rated 5-6

Poor condition

6.8%

17 of 249 rated 4 or below

In-state Poor-share rank

#11 of 99

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

Condition distribution

Share of 249 NBI-tracked bridges by lowest applicable component rating.

Good

48.6% (121)

Fair

44.6% (111)

Poor

6.8% (17)

Carroll County's Poor-condition bridges carry 2,088 vehicle crossings a day

That is 1.4% of the county's reported daily bridge traffic on 6.9% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 123 crossings a day against 607 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 248 of 249 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

43% of Carroll County's bridges have passed the 50-year mark

107 of the 249 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 48.6% 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 31.1% of the county's Poor-condition bridge traffic

FM over BRUSHY FORK CREEK, built 1964, carries 650 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 17-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 2,088 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

14
1910s

3
1920s

3
1930s

4
1940s

4
1950s

20
1960s

34
1970s

39
1980s

32
1990s

38
2000s

34
2010s

20
2020s

4

What this shows Construction peaked in the 1970s, when 39 of the county's bridges still in the inventory were built, which is 15.7% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year (1977) matches the Iowa average (1979).

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

The 5 Iowa counties nearest Carroll County in number of bridges, with their condition splits. Its 6.8% Poor share is the 1st-lowest of these 6. Its average build year of 1977 against a peer-group mean of 1974 is in line with the group.

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

Bridge inventory size and condition shares for Carroll County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Clayton County	256	30.5%	59%	10.5%	1964
Carroll County (this page)	249	48.6%	44.6%	6.8%	1977
Cherokee County	248	34.3%	36.7%	29%	1968
Poweshiek County	248	25%	33.1%	41.9%	1974
Jackson County	246	26.4%	56.5%	17.1%	1983
Hardin County	241	36.1%	36.1%	27.8%	1981

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

Similar inventory size

Nearest county inventories outside IA (249 bridges here).

Brevard County, FL · 249 bridges
Phillips County, KS · 249 bridges
Lawrence County, OH · 249 bridges
Van Zandt County, TX · 249 bridges

Similar average build year

Nearest mean year-built outside IA (1977 here).

San Diego County, CA · avg 1977 · 1,632 bridges
King County, WA · avg 1977 · 1,238 bridges
Riverside County, CA · avg 1977 · 1,117 bridges
Shelby County, TN · avg 1977 · 1,077 bridges

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

All 249 Good 121 Fair 111 Poor 17

Good-condition bridges (121)

Sort:

Carroll County Bridge Snapshot

Condition distribution

Carroll County's Poor-condition bridges carry 2,088 vehicle crossings a day

43% of Carroll County's bridges have passed the 50-year mark

One structure carries 31.1% of the county's Poor-condition bridge traffic

How Carroll 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

Good-condition bridges (121)

LOCAL

LOCAL

LOCAL

LOCAL

220TH ST

LOCAL

LOCAL

LOCAL

FM

FM

KITTYHAWK AVE

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

LOCAL

FM

FM

LOCAL

LOCAL

LOCAL

FM

FM

US 30

GRANITE AVE

US 71

US 30

US 71

LOCAL

FM

QUAIL AVE

M68 DELTA AVE

FM

FM

LOCAL

LOCAL

US 71

IA 141

FM

FM

GRANT RD

FM

310TH ST

BASS STREET

FM

110TH ST

110TH ST

Related