County profile · official public datasets

Shelby County, IA

207 public highway bridges tracked in the FHWA National Bridge Inventory: 36.2% rated Good, 54.1% Fair, 9.7% Poor.

207
Public bridges: 36.2%
Good condition: 9.7%
Poor condition

The verdict

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

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

Top 18%
lowest Poor share in state: 9.7%
Poor-condition share: 207
public highway bridges: 1979
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.

Shelby County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Shelby County ranks #18 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 9.7%). Shelby County, Iowa contains 207 public highway bridges. Roughly 36.2% are rated “Good,” 54.1% “Fair,” and 9.7% “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

207

Public highway bridges in Shelby County

Good condition

36.2%

75 of 207 rated 7-9

Fair condition

54.1%

112 of 207 rated 5-6

Poor condition

9.7%

20 of 207 rated 4 or below

In-state Poor-share rank

#18 of 99

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

Condition distribution

Share of 207 NBI-tracked bridges by lowest applicable component rating.

Good

36.2% (75)

Fair

54.1% (112)

Poor

9.7% (20)

Shelby County's Poor-condition bridges carry 1,151 vehicle crossings a day

That is 1.6% of the county's reported daily bridge traffic on 9.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 61 crossings a day against 237 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 205 of 207 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

48.3% of Shelby County's bridges have passed the 50-year mark

100 of the 207 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 36.2% 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 36.2% of the county's Poor-condition bridge traffic

F24 over SMALL STREAM, built 1938, carries 417 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 20-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 1,151 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

1
1910s

2
1920s

6
1930s

3
1940s

6
1950s

45
1960s

27
1970s

14
1980s

19
1990s

24
2000s

23
2010s

29
2020s

8

What this shows Construction peaked in the 1950s, when 45 of the county's bridges still in the inventory were built, which is 21.7% of those with a recorded year. That cohort is now 65 to 74 years old in the 2024 inventory. Its average build year (1979) matches the Iowa average (1979).

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

The 5 Iowa counties nearest Shelby County in number of bridges, with their condition splits. Its 9.7% Poor share is the 1st-lowest of these 6. Its average build year of 1979 against a peer-group mean of 1978 is in line with the group.

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

Bridge inventory size and condition shares for Shelby County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Floyd County	213	49.8%	35.7%	14.6%	1984
Howard County	210	41.9%	35.2%	22.9%	1984
Montgomery County	210	21%	53.8%	25.2%	1973
Washington County	207	39.6%	44.4%	15.9%	1980
Shelby County (this page)	207	36.2%	54.1%	9.7%	1979
Audubon County	206	33.5%	48.1%	18.4%	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 Shelby 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 Shelby County, both outside Iowa so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside IA (207 bridges here).

Marin County, CA · 207 bridges
Las Animas County, CO · 207 bridges
Richland County, LA · 207 bridges
Atlantic County, NJ · 207 bridges

Similar average build year

Nearest mean year-built outside IA (1979 here).

Pima County, AZ · avg 1979 · 1,150 bridges
Jefferson County, KY · avg 1979 · 662 bridges
Spartanburg County, SC · avg 1979 · 638 bridges
McPherson County, KS · avg 1979 · 586 bridges

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

All 207 Good 75 Fair 112 Poor 20

All bridges (207)

Sort:

Shelby County Bridge Snapshot

Condition distribution

Shelby County's Poor-condition bridges carry 1,151 vehicle crossings a day

48.3% of Shelby County's bridges have passed the 50-year mark

One structure carries 36.2% of the county's Poor-condition bridge traffic

How Shelby 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 (207)

LOCAL

LOCAL

LOCAL

CEDAR RD

SO M 16

2100TH ST

IA 44

LOCAL

FM

LOCAL

IA 44

LOCAL

FM

LOCAL

FM

LOCAL

SPRUCE LOOP

FM

LOCAL

FM

LOCAL

FM RD F16

FM RD F32

FM

US 59

FM

FM RD F16

FM

US 59

FM RD F-32

LOCAL

US 59

FM

EXCHANGE ST

F24

F24

IA 44

LOCAL

FM

FM RD F32

LOCAL

FM

FM

IA 44

FM

IA 44

US 59

FM

FM RD M56

US 59

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