Total bridges
372
Public highway bridges in Johnson County
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.
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.
When Johnson County's bridges were built
372 bridges with a recorded construction year, grouped by decade
- 1900s 15
1900–1909
15 bridges
- 1910s 9
1910–1919
9 bridges
- 1920s 7
1920–1929
7 bridges
- 1930s 10
1930–1939
10 bridges
- 1940s 3
1940–1949
3 bridges
- 1950s 22
1950–1959
22 bridges
- 1960s
1960–1969
52 bridges
- 1970s
1970–1979
71 bridges
- 1980s
1980–1989
40 bridges
- 1990s
1990–1999
46 bridges
- 2000s
2000–2009
35 bridges
- 2010s 24
2010–2019
24 bridges
- 2020s
2020–2029
38 bridges
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.
| 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 bridges (372)
VAN BUREN ST
PoorOver: RALSTON CREEK
079061500, Johnson, IA
Built 1935 Load: 17.0 t ADT: 1,082
SW 520TH ST
PoorOver: DEER CREEK
078082001, Johnson, IA
Built 1900 Load: 17.5 t ADT: 35
120TH ST
PoorOver: STREAM
081050901, Johnson, IA
Built 1952 Load: 18.8 t ADT: 30
160TH ST
PoorOver: BR MILL CR
081052201, Johnson, IA
Built 1955 Load: 18.8 t ADT: 60
FM AMANA RD
PoorOver: BR IOWA RIVER
081082403, Johnson, IA
Built 1935 Load: 21.6 t ADT: 130
SW ANGLE RD
PoorOver: BR OLD MANS CR
078081203, Johnson, IA
Built 1920 Load: 22.7 t ADT: 92
WASHINGTON ST
PoorOver: RALSTON CREEK
079061000, Johnson, IA
Built 1910 Load: 22.9 t ADT: 2,487
BENTON ST
PoorOver: RALSTON CREEK
079061500, Johnson, IA
Built 1935 Load: 24.5 t ADT: 449
KIRKWOOD AVE
PoorOver: RALSTON CREEK
079061500, Johnson, IA
Built 1935 Load: 24.5 t ADT: 4,693
JOHNSON ST
PoorOver: RALSTON CREEK
079061000, Johnson, IA
Built 1930 Load: 25.9 t ADT: 2,356
THIRD AVE
PoorOver: SO BR RALSTON CREEK
079061400, Johnson, IA
Built 1957 Load: 26.1 t ADT: 341
SIOUX AVE
PoorOver: STREAM
079053102, Johnson, IA
Built 1966 Load: 26.5 t ADT: 234
FM 520TH ST
PoorOver: IOWA RIVER
078062301, Johnson, IA
Built 1971 Load: 27.2 t ADT: 2,060
GREEN CASTLE AV
PoorOver: SMALL STREAM
079071802, Johnson, IA
Built 1900 Load: 28.1 t ADT: 46
CENTER AVE
PoorOver: RALSTON CREEK
079061400, Johnson, IA
Built 1957 Load: 29.0 t ADT: 330
FM SW NAPLES AV
PoorOver: CROOKED CR
078063202, Johnson, IA
Built 1942 Load: 29.7 t ADT: 70
GILBERT ST
PoorOver: RALSTON CREEK
079061500, Johnson, IA
Built 1972 Load: 30.2 t ADT: 14,025
FM SW BAYRTWN R
PoorOver: STREAM
078072303, Johnson, IA
Built 1964 Load: 30.8 t ADT: 240
IOWA AVE
PoorOver: IOWA RIVER
79060900, Johnson, IA
Built 1916 Load: 31.9 t ADT: 5,400
DODGE ST
PoorOver: OVER IAIS RR
079061500, Johnson, IA
Built 1970 Load: 32.7 t ADT: 4,688
FM 520TH ST
PoorOver: PECHMAN CREEK
078062403, Johnson, IA
Built 1974 Load: 33.1 t ADT: 880
IA 1 NB
PoorOver: IOWA RIVER
079061000, Johnson, IA
Built 1915 Load: 38.5 t ADT: 10,950
Read our methodology - how this data is sourced, computed, and verified.
Related
Data sourced from official public datasets. See our methodology for details. Retrieved and formatted by PlainBridges
Every figure on PlainBridges is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. NBI condition categories reflect the latest reported inventory record, not a live safety, closure, or travel decision.