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.

Total bridges

299

Public highway bridges in Ada County

Good condition

41.8%

125 of 299 rated 7-9

Fair condition

58.2%

174 of 299 rated 5-6

Poor condition

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.

1930s

3
1940s

5
1950s

10
1960s

41
1970s

38
1980s

29
1990s

83
2000s

41
2010s

34
2020s

15

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.

Bridge inventory size and condition shares for Ada County and the 5 Idaho counties closest to it in inventory size
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.

All 299 Good 125 Fair 174 Poor 0

Good-condition bridges (125)

Sort:

Ada County Bridge Snapshot

Condition distribution

25.4% of Ada County's bridges have passed the 50-year mark

How Ada County compares with Idaho's closest counties by inventory size

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

Good-condition bridges (125)

SMA 9773;LINDER RD

STC3768;HUBBARD

US 20 26 RAMP

SMA 7143;USTICK RD

SH 55

STODDARD ROAD

SMA9613;MCMILLAN R

STC 7673;GOWEN RD

STP7851;MCDERMOTT

STC 9503;GEKELER

STC 3767;MUNGER RD

SMA3773;LINDER RD

SMA7288;HILLRDPKWY

SH 21

I 184

SMA 7343;CHERRY LN

SMA 9793; MAIN ST

STP 7073;COLE RD

STC 7393;OWYHEE ST

STC 3784;E KUNA RD

SHOSHONE STREET

US 20

STP 7343;MAIN ST

BROKEN HORN ROAD

S3760;FLTG FEATHER

S3760;FLTG FEATHER

SMA9243;VICTORY RD

PINE AVE

STC9573:E MALLARD

SUNDERLAND DR.

I 84 EBL

STP 9183;TEN MILE

ESTHER SIMPLOT PK

SH 55

SMA 7029;EAGLE RD

I 84 WBL

STP8973;ORCHARD ST

SMA9803;MAPLE GRVE

SH 16

LAKE HAZEL RD

NHM7683;GOWEN RD

STP3764;AMITY RD

STC 7233;ROOSEVELT

SMA 7028;BEACON LT

SMA9803;MAPLE GRVE

US 20; I 84B

I 84 EBL

SMA 9423;EISENMAN

SMA 7028;BEACON LT

N. GARDEN ST

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