Total bridges
165
Public highway bridges in Hamilton County
County profile · official public datasets
Hamilton County, IA
165 public highway bridges tracked in the FHWA National Bridge Inventory: 39.4% rated Good, 40% Fair, 20.6% Poor.
- 165
- Public bridges
- 39.4%
- Good condition
- 20.6%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Hamilton County pairs a higher-than-median Poor-condition share among rated counties in the state with an older average build year than the state inventory.
- 57th
- of 99 on Poor share
- 20.6%
- Poor-condition share
- 165
- public highway bridges
- 1970
- 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.
Hamilton County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Hamilton County ranks #57 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 20.6%). Hamilton County, Iowa contains 165 public highway bridges. Roughly 39.4% are rated “Good,” 40% “Fair,” and 20.6% “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
39.4%
65 of 165 rated 7-9
Fair condition
40%
66 of 165 rated 5-6
Poor condition
20.6%
34 of 165 rated 4 or below
In-state Poor-share rank
#57 of 99
Among Iowa counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 165 NBI-tracked bridges by lowest applicable component rating.
Good 39.4% (65)
Fair 40% (66)
Poor 20.6% (34)
Hamilton County's Poor-condition bridges carry 4,871 vehicle crossings a day
That is 1.5% of the county's reported daily bridge traffic on 20.1% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 148 crossings a day against 1,889 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 164 of 165 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
57.6% of Hamilton County's bridges have passed the 50-year mark
95 of the 165 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 39.4% 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 14.3% of the county's Poor-condition bridge traffic
FM over SKUNK RIVER, built 1974, carries 698 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 34-bridge count understates how much of the daily burden sits on a single crossing.
Share is of the 4,871 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When Hamilton County's bridges were built
165 bridges with a recorded construction year, grouped by decade
- 1900s 2
1900–1909
2 bridges
- 1910s 6
1910–1919
6 bridges
- 1920s
1920–1929
18 bridges
- 1930s 4
1930–1939
4 bridges
- 1940s 5
1940–1949
5 bridges
- 1950s 16
1950–1959
16 bridges
- 1960s
1960–1969
23 bridges
- 1970s
1970–1979
41 bridges
- 1980s 6
1980–1989
6 bridges
- 1990s 14
1990–1999
14 bridges
- 2000s 14
2000–2009
14 bridges
- 2010s 14
2010–2019
14 bridges
- 2020s 2
2020–2029
2 bridges
What this shows Construction peaked in the 1970s, when 41 of the county's bridges still in the inventory were built, which is 24.8% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year is 1970, 9 years older than the Iowa average of 1979.
How Hamilton County compares with Iowa's closest counties by inventory size
The 5 Iowa counties nearest Hamilton County in number of bridges, with their condition splits. Its 20.6% Poor share is the 4th-lowest of these 6. Its average build year of 1970 against a peer-group mean of 1981 is 11 years older.
Showing the 5 closest of 98 Iowa counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Clarke County | 168 | 27.4% | 41.1% | 31.5% | 1977 |
| Greene County | 168 | 35.1% | 50% | 14.9% | 1973 |
| Mitchell County | 167 | 47.3% | 42.5% | 10.2% | 1980 |
| Davis County | 165 | 44.8% | 29.7% | 25.5% | 1985 |
| Hamilton County (this page) | 165 | 39.4% | 40% | 20.6% | 1970 |
| Wayne County | 163 | 44.2% | 37.4% | 18.4% | 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 Hamilton 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 Hamilton County, both outside Iowa so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside IA (165 bridges here).
- Cleburne County, AL · 165 bridges
- Randolph County, AL · 165 bridges
- Plumas County, CA · 165 bridges
- Leon County, FL · 165 bridges
Similar average build year
Nearest mean year-built outside IA (1970 here).
- Hamilton County, OH · avg 1970 · 783 bridges
- Yavapai County, AZ · avg 1970 · 543 bridges
- Garfield County, OK · avg 1970 · 504 bridges
- San Luis Obispo County, CA · avg 1970 · 401 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
Fair-condition bridges (66)
LOCAL
FairOver: CREEK
088250906, Hamilton, IA
Built 1918 Load: 37.5 t ADT: 11
SR D-20
FairOver: I-35
AT JUNCTION WITH D20, Hamilton, IA
Built 1972 Load: 37.9 t ADT: 828
I-35
FairOver: TUTTLE CREEK
0.2 MILE N OF JCT US 20, Hamilton, IA
Built 1967 Load: 39.2 t ADT: 16,800
US 20
FairOver: DRAINAGE DITCH #4
1.8 MILES EAST OF US 69, Hamilton, IA
Built 1968 Load: 40.2 t ADT: 9,600
IA 175
FairOver: S SKUNK RIVER
1.0 MILE WEST OF JCT I-35, Hamilton, IA
Built 1979 Load: 40.3 t ADT: 1,790
US 69
FairOver: CC RR
0.8 MILE N OF JCT SR D25, Hamilton, IA
Built 1973 Load: 41.5 t ADT: 1,160
I 35 NB
FairOver: STREAM
1.8 MILES N OF SEC RD D20, Hamilton, IA
Built 1972 Load: 42.0 t ADT: 8,200
SB I-35
FairOver: STREAM
1.8 MILES N OF SEC RD D20, Hamilton, IA
Built 1972 Load: 42.0 t ADT: 8,200
DES MOINES ST
FairOver: BREWER CREEK
000000000, Hamilton, IA
Built 1989 Load: 42.2 t ADT: 3,175
OVERPASS DR
FairOver: CC RR
000000000, Hamilton, IA
Built 1931 Load: 47.7 t ADT: 3,353
US 69
FairOver: DRAINAGE DITCH
0.5 mi. N of N jct. 175, Hamilton, IA
Built 2009 Load: 51.8 t ADT: 1,620
FM
FairOver: IOWAY CREEK
086262202, Hamilton, IA
Built 1982 Load: 56.9 t ADT: 559
NB I-35
FairOver: CO RD D-25
AT JUNCTION WITH SR D25, Hamilton, IA
Built 1974 Load: 75.5 t ADT: 7,950
LOCAL
FairOver: DRAINAGE DITCH
087240703, Hamilton, IA
Built 1971 Load: 99.9 t ADT: 20
FM
FairOver: DRAINAGE DITCH
087253601, Hamilton, IA
Built 1976 Load: 99.9 t ADT: 509
FM
FairOver: BUCK CREEK
089252206, Hamilton, IA
Built 1975 Load: 99.9 t ADT: 199
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.