County profile · official public datasets

Johnson County, IA

372 public highway bridges tracked in the FHWA National Bridge Inventory: 39.5% rated Good, 50.3% Fair, 10.2% Poor.

372
Public bridges: 39.5%
Good condition: 10.2%
Poor condition

The verdict

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

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

Top 21%
lowest Poor share in state: 10.2%
Poor-condition share: 372
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.

Johnson County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Johnson County ranks #21 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 10.2%). Johnson County, Iowa contains 372 public highway bridges. Roughly 39.5% are rated “Good,” 50.3% “Fair,” and 10.2% “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

372

Public highway bridges in Johnson County

Good condition

39.5%

147 of 372 rated 7-9

Fair condition

50.3%

187 of 372 rated 5-6

Poor condition

10.2%

38 of 372 rated 4 or below

In-state Poor-share rank

#21 of 99

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

Condition distribution

Share of 372 NBI-tracked bridges by lowest applicable component rating.

Good

39.5% (147)

Fair

50.3% (187)

Poor

10.2% (38)

Johnson County's Poor-condition bridges carry 55,995 vehicle crossings a day

That is 3.5% of the county's reported daily bridge traffic on 10.2% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 1,474 crossings a day against 5,176 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 372 of 372 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

41.9% of Johnson County's bridges have passed the 50-year mark

156 of the 372 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 39.5% 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 25% of the county's Poor-condition bridge traffic

GILBERT ST over RALSTON CREEK, built 1972, carries 14,025 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 38-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 55,995 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

15
1910s

9
1920s

7
1930s

10
1940s

3
1950s

22
1960s

52
1970s

71
1980s

40
1990s

46
2000s

35
2010s

24
2020s

38

What this shows Construction peaked in the 1970s, when 71 of the county's bridges still in the inventory were built, which is 19.1% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year (1979) matches the Iowa average (1979).

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

The 5 Iowa counties nearest Johnson County in number of bridges, with their condition splits. Its 10.2% Poor share is the 3rd-lowest of these 6. Its average build year of 1979 against a peer-group mean of 1982 is in line with the group.

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

Bridge inventory size and condition shares for Johnson County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Jasper County	382	38.5%	32.5%	29.1%	1977
Benton County	374	34.2%	42.8%	23%	1984
Clinton County	372	66.7%	30.4%	3%	1986
Johnson County (this page)	372	39.5%	50.3%	10.2%	1979
Fayette County	362	35.1%	40.3%	24.6%	1974
Dubuque County	346	50.6%	40.8%	8.7%	1989

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

Similar inventory size

Nearest county inventories outside IA (372 bridges here).

Harper County, KS · 372 bridges
Harvey County, KS · 372 bridges
Wharton County, TX · 372 bridges
Solano County, CA · 373 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 372 Good 147 Fair 187 Poor 38

Fair-condition bridges (187)

Sort:

Johnson County Bridge Snapshot

Condition distribution

Johnson County's Poor-condition bridges carry 55,995 vehicle crossings a day

41.9% of Johnson County's bridges have passed the 50-year mark

One structure carries 25% of the county's Poor-condition bridge traffic

How Johnson 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 (187)

FM IVY AVE

FM ROHRET RD

FM SW BLK HWK D

SW EAGLE AVE

280TH ST NE

FM SO FRONT ST

FM PRARE DU CHN

NEWPORT RD

FM 250TH ST

FM JAMES AVE

FM 250TH ST

SUTLIFF RD

SEVEN SIS RD

NE HICKORY H RD

LINN-JOHNSON RD

FM 120TH ST

LOCAL

LINN-JOHNSON RD

FM SW 540TH AVE

SW BUCHANAN AVE

FM ELY RD

BENTON ST

I 80 WB

FM AM LEGION RD

COSGROVE RD

LINN-JOHNSON RD

OBSERVATORY AVE

WB I-80

BROOKSIDE DR

SW BLK DIAMOND

SB US 218

FM

I-80

SB US 218

IA 1

NAPOLEON ST

DUBUQUE ST

Related