Total bridges
299
Public highway bridges in Ada County
County profile · official public datasets
Ada County, ID
299 public highway bridges tracked in the FHWA National Bridge Inventory: 41.8% rated Good, 58.2% Fair, 0% Poor.
- 299
- Public bridges
- 41.8%
- Good condition
- 0%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Ada County pairs a top-5% lowest Poor-condition share among rated counties in the state with a newer average build year than the state inventory.
- Top 2%
- lowest Poor share in state
- 0%
- Poor-condition share
- 299
- public highway bridges
- 1989
- 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.
Ada County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Ada County ranks #1 of 44 Idaho counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 0%). Ada County, Idaho contains 299 public highway bridges. Roughly 41.8% are rated “Good,” 58.2% “Fair,” and 0% “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
41.8%
125 of 299 rated 7-9
Fair condition
58.2%
174 of 299 rated 5-6
Poor condition
0%
0 of 299 rated 4 or below
In-state Poor-share rank
#1 of 44
Among Idaho counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 299 NBI-tracked bridges by lowest applicable component rating.
Good 41.8% (125)
Fair 58.2% (174)
Poor 0% (0)
25.4% of Ada County's bridges have passed the 50-year mark
76 of the 299 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 41.8% 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.
When Ada County's bridges were built
299 bridges with a recorded construction year, grouped by decade
- 1930s 3
1930–1939
3 bridges
- 1940s 5
1940–1949
5 bridges
- 1950s 10
1950–1959
10 bridges
- 1960s
1960–1969
41 bridges
- 1970s
1970–1979
38 bridges
- 1980s 29
1980–1989
29 bridges
- 1990s
1990–1999
83 bridges
- 2000s
2000–2009
41 bridges
- 2010s
2010–2019
34 bridges
- 2020s 15
2020–2029
15 bridges
What this shows Construction peaked in the 1990s, when 83 of the county's bridges still in the inventory were built, which is 27.8% of those with a recorded year. That cohort is now 25 to 34 years old in the 2024 inventory. Its average build year is 1989, 10 years newer than the Idaho average of 1979.
How Ada County compares with Idaho's closest counties by inventory size
The 5 Idaho counties nearest Ada County in number of bridges, with their condition splits. Its 0% Poor share is the 1st-lowest of these 6. Its average build year of 1989 against a peer-group mean of 1976 is 13 years newer.
Showing the 5 closest of 43 Idaho counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Ada County (this page) | 299 | 41.8% | 58.2% | 0% | 1989 |
| Canyon County | 292 | 27.7% | 69.5% | 2.7% | 1984 |
| Bingham County | 263 | 17.1% | 79.5% | 3.4% | 1975 |
| Shoshone County | 260 | 21.5% | 68.8% | 9.6% | 1971 |
| Idaho County | 215 | 37.2% | 56.7% | 6% | 1975 |
| Bonneville County | 213 | 30.5% | 66.7% | 2.8% | 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 Ada 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 Ada County, both outside Idaho so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside ID (299 bridges here).
- Beaver County, PA · 299 bridges
- Northumberland County, PA · 299 bridges
- DeKalb County, AL · 300 bridges
- Christian County, KY · 300 bridges
Similar average build year
Nearest mean year-built outside ID (1989 here).
- Harris County, TX · avg 1989 · 4,029 bridges
- Mecklenburg County, NC · avg 1989 · 746 bridges
- Buffalo County, NE · avg 1989 · 459 bridges
- Brazos County, TX · avg 1989 · 370 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
Poor-condition bridges (0)
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.