County profile · official public datasets

Linn County, IA

506 public highway bridges tracked in the FHWA National Bridge Inventory: 46.4% rated Good, 47.2% Fair, 6.3% Poor.

506
Public bridges: 46.4%
Good condition: 6.3%
Poor condition

The verdict

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

Linn County pairs a top-10% lowest Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

Top 6%
lowest Poor share in state: 6.3%
Poor-condition share: 506
public highway bridges: 1987
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.

Linn County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Linn County ranks #6 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 6.3%). Linn County, Iowa contains 506 public highway bridges. Roughly 46.4% are rated “Good,” 47.2% “Fair,” and 6.3% “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

506

Public highway bridges in Linn County

Good condition

46.4%

235 of 506 rated 7-9

Fair condition

47.2%

239 of 506 rated 5-6

Poor condition

6.3%

32 of 506 rated 4 or below

In-state Poor-share rank

#6 of 99

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

Condition distribution

Share of 506 NBI-tracked bridges by lowest applicable component rating.

Good

46.4% (235)

Fair

47.2% (239)

Poor

6.3% (32)

Linn County's Poor-condition bridges carry 80,824 vehicle crossings a day

That is 3.1% of the county's reported daily bridge traffic on 6.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 2,526 crossings a day against 2,954 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 505 of 506 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

20.2% of Linn County's bridges have passed the 50-year mark

102 of the 506 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 46.4% 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 13.3% of the county's Poor-condition bridge traffic

8TH AVE over INDIAN CREEK, built 1988, carries 10,789 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 32-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 80,824 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

pre-1900

2
1900s

5
1910s

3
1920s

8
1930s

6
1940s

7
1950s

17
1960s

24
1970s

96
1980s

90
1990s

90
2000s

86
2010s

56
2020s

16

What this shows Construction peaked in the 1970s, when 96 of the county's bridges still in the inventory were built, which is 19% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year is 1987, 8 years newer than the Iowa average of 1979.

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

The 5 Iowa counties nearest Linn County in number of bridges, with their condition splits. Its 6.3% Poor share is the 2nd-lowest of these 6. Its average build year of 1987 against a peer-group mean of 1983 is in line with the group.

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

Bridge inventory size and condition shares for Linn County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Pottawattamie County	557	38.8%	51.9%	9.3%	1981
Polk County	545	57.8%	35.8%	6.4%	1986
Linn County (this page)	506	46.4%	47.2%	6.3%	1987
Black Hawk County	489	52.8%	40.7%	6.5%	1983
Woodbury County	455	39.3%	39.6%	21.1%	1985
Sioux County	449	62.4%	34.7%	2.9%	1982

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

Similar inventory size

Nearest county inventories outside IA (506 bridges here).

Saunders County, NE · 506 bridges
Essex County, NJ · 505 bridges
Monmouth County, NJ · 505 bridges
Oakland County, MI · 508 bridges

Similar average build year

Nearest mean year-built outside IA (1987 here).

St. Louis County, MO · avg 1987 · 912 bridges
Ellis County, TX · avg 1987 · 691 bridges
St. Louis County, MN · avg 1987 · 663 bridges
Palm Beach County, FL · avg 1987 · 610 bridges

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

All 506 Good 235 Fair 239 Poor 32

All bridges (506)

Sort:

Linn County Bridge Snapshot

Condition distribution

Linn County's Poor-condition bridges carry 80,824 vehicle crossings a day

20.2% of Linn County's bridges have passed the 50-year mark

One structure carries 13.3% of the county's Poor-condition bridge traffic

How Linn 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 (506)

MT VERNON RD

76TH AVE SW

ANDERSON RD

7TH AVE

UP-BOULDER RD

I 380 SB

WB 15TH AVE

IA 13

GLASS RD

SB I-380

SB I-380

C STREET

I 380 NB

J ST

BLAIRSFERRY RD

NB I-380

MAIN ST

LINN-BENTON RD

SB I-380

NB I-380

IA 13

NB I 380

NB US 151

SB US 151-IA 13

INK ROAD

COTTAGE GR.PWY

WESTWOOD DR NW

NB I-380

A AVE

C ST RD

SPANISH RD

NB US 151& IA 13

RAMP BR D-3

IA 100

FRANKLIN ST

OLD RIVER RD

IVANHOE RD

I 380 NB

COTTAGE GROVE

MT VERNON RD

SB I-380

US 30 WB

MILL ST.

GRANT ST

CHAIN BRIDGE ROAD

60TH AVE SW

E AVE

J AVE NE

5TH ST

W GRANT ST

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