Total bridges
135
Public highway bridges in Boone County
County profile · official public datasets
Boone County, IA
135 public highway bridges tracked in the FHWA National Bridge Inventory: 27.4% rated Good, 43% Fair, 29.6% Poor.
- 135
- Public bridges
- 27.4%
- Good condition
- 29.6%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Boone 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.
- 79th
- of 99 on Poor share
- 29.6%
- Poor-condition share
- 135
- public highway bridges
- 1955
- 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.
Boone County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Boone County ranks #79 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 29.6%). Boone County, Iowa contains 135 public highway bridges. Roughly 27.4% are rated “Good,” 43% “Fair,” and 29.6% “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
27.4%
37 of 135 rated 7-9
Fair condition
43%
58 of 135 rated 5-6
Poor condition
29.6%
40 of 135 rated 4 or below
In-state Poor-share rank
#79 of 99
Among Iowa counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 135 NBI-tracked bridges by lowest applicable component rating.
Good 27.4% (37)
Fair 43% (58)
Poor 29.6% (40)
Boone County's Poor-condition bridges carry 3,048 vehicle crossings a day
That is 2.8% of the county's reported daily bridge traffic on 30.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 76 crossings a day against 919 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 132 of 135 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
66.7% of Boone County's bridges have passed the 50-year mark
90 of the 135 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 27.4% 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 25.2% of the county's Poor-condition bridge traffic
FM over DES MOINES RIVER, built 1972, carries 769 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 40-bridge count understates how much of the daily burden sits on a single crossing.
Share is of the 3,048 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When Boone County's bridges were built
135 bridges with a recorded construction year, grouped by decade
- 1900s
1900–1909
21 bridges
- 1910s
1910–1919
14 bridges
- 1920s
1920–1929
11 bridges
- 1930s
1930–1939
10 bridges
- 1940s 5
1940–1949
5 bridges
- 1950s 6
1950–1959
6 bridges
- 1960s
1960–1969
15 bridges
- 1970s
1970–1979
13 bridges
- 1980s 7
1980–1989
7 bridges
- 1990s 7
1990–1999
7 bridges
- 2000s
2000–2009
10 bridges
- 2010s
2010–2019
13 bridges
- 2020s 3
2020–2029
3 bridges
What this shows Construction peaked in the 1900s, when 21 of the county's bridges still in the inventory were built, which is 15.6% of those with a recorded year. That cohort is now 115 to 124 years old in the 2024 inventory. Its average build year is 1955, 24 years older than the Iowa average of 1979.
How Boone County compares with Iowa's closest counties by inventory size
The 5 Iowa counties nearest Boone County in number of bridges, with their condition splits. Its 29.6% Poor share is the 6th-lowest of these 6. Its average build year of 1955 against a peer-group mean of 1978 is 23 years older.
Showing the 5 closest of 98 Iowa counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Clay County | 151 | 35.8% | 54.3% | 9.9% | 1982 |
| Muscatine County | 144 | 34.7% | 43.8% | 21.5% | 1979 |
| Hancock County | 138 | 39.9% | 39.9% | 20.3% | 1981 |
| Palo Alto County | 135 | 23% | 58.5% | 18.5% | 1973 |
| Boone County (this page) | 135 | 27.4% | 43% | 29.6% | 1955 |
| Monroe County | 130 | 26.2% | 49.2% | 24.6% | 1977 |
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 Boone 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 Boone County, both outside Iowa so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside IA (135 bridges here).
- Nevada County, CA · 135 bridges
- Meriwether County, GA · 135 bridges
- Steuben County, IN · 135 bridges
- Warren County, IN · 135 bridges
Similar average build year
Nearest mean year-built outside IA (1955 here).
- Brown County, TX · avg 1955 · 223 bridges
- Beadle County, SD · avg 1955 · 152 bridges
- Duval County, TX · avg 1955 · 121 bridges
- Bath County, VA · avg 1955 · 73 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
Fair-condition bridges (58)
FM
FairOver: BLUFF CREEK
084270801, Boone, IA
Built 1956 Load: 41.0 t ADT: 478
LOCAL
FairOver: MONTGOMERY CREEK
085263601, Boone, IA
Built 1994 Load: 43.7 t ADT: 30
US 169
FairOver: UP RR
0.2 MILE N OF N JCT US 30, Boone, IA
Built 1984 Load: 44.4 t ADT: 1,890
IA 17
FairOver: PRAIRIE CREEK
2.4 MILES N OF JCT SR E26, Boone, IA
Built 1979 Load: 45.7 t ADT: 2,260
FM
FairOver: BEAVER CREEK
082283409, Boone, IA
Built 1920 Load: 48.7 t ADT: 139
FM E-41
FairOver: STREAM
083270604, Boone, IA
Built 1970 Load: 56.0 t ADT: 450
IA 17
FairOver: BIG CREEK
1.9 MILES S OF JCT US 30, Boone, IA
Built 1961 Load: 64.3 t ADT: 5,200
US 30
FairOver: HONEY CREEK
0.7 mi. W of Jct. SR R23, Boone, IA
Built 1962 Load: 99.9 t ADT: 8,800
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.