County profile · official public datasets

Boise County, ID

88 public highway bridges tracked in the FHWA National Bridge Inventory: 46.6% rated Good, 47.7% Fair, 5.7% Poor.

88
Public bridges: 46.6%
Good condition: 5.7%
Poor condition

The verdict

According to the Federal Highway Administration's 2024 National Bridge Inventory.

Boise County posts a higher-than-median Poor-condition share among rated counties in the state across rated county bridge inventory.

25th
of 44 on Poor share: 5.7%
Poor-condition share: 88
public highway bridges: 1978
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.

Boise County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Boise County ranks #25 of 44 Idaho counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 5.7%). Boise County, Idaho contains 88 public highway bridges. Roughly 46.6% are rated “Good,” 47.7% “Fair,” and 5.7% “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

Public highway bridges in Boise County

Good condition

46.6%

41 of 88 rated 7-9

Fair condition

47.7%

42 of 88 rated 5-6

Poor condition

5.7%

5 of 88 rated 4 or below

In-state Poor-share rank

#25 of 44

Among Idaho counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 88 NBI-tracked bridges by lowest applicable component rating.

Good

46.6% (41)

Fair

47.7% (42)

Poor

5.7% (5)

Boise County's Poor-condition bridges carry 220 vehicle crossings a day

That is 0.2% of the county's reported daily bridge traffic on 5.7% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 44 crossings a day against 1,069 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 88 of 88 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

46.6% of Boise County's bridges have passed the 50-year mark

41 of the 88 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 46.6% 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 45.5% of the county's Poor-condition bridge traffic

ANDERSON CREEK RD over ANDERSON CREEK, built 1983, carries 100 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 5-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 220 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1910s

1
1920s

1
1930s

3
1940s

3
1950s

10
1960s

13
1970s

14
1980s

13
1990s

15
2000s

7
2010s

6
2020s

2

What this shows Construction peaked in the 1990s, when 15 of the county's bridges still in the inventory were built, which is 17% of those with a recorded year. That cohort is now 25 to 34 years old in the 2024 inventory. Its average build year (1978) matches the Idaho average (1979).

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

The 5 Idaho counties nearest Boise County in number of bridges, with their condition splits. Its 5.7% Poor share is the 3rd-lowest of these 6. Its average build year of 1978 against a peer-group mean of 1975 is in line with the group.

Showing the 5 closest of 43 Idaho counties eligible for comparison.

Bridge inventory size and condition shares for Boise County and the 5 Idaho counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Blaine County	96	25%	71.9%	3.1%	1978
Clearwater County	88	43.2%	51.1%	5.7%	1973
Boise County (this page)	88	46.6%	47.7%	5.7%	1978
Adams County	87	32.2%	57.5%	10.3%	1975
Boundary County	83	32.5%	57.8%	9.6%	1982
Gooding County	80	16.3%	76.3%	7.5%	1965

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 Boise 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 Boise County, both outside Idaho so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside ID (88 bridges here).

Chicot County, AR · 88 bridges
Prairie County, AR · 88 bridges
Grand County, CO · 88 bridges
Spalding County, GA · 88 bridges

Similar average build year

Nearest mean year-built outside ID (1978 here).

Orange County, CA · avg 1978 · 1,164 bridges
Sumner County, KS · avg 1978 · 659 bridges
Allen County, IN · avg 1978 · 613 bridges
Livingston County, IL · avg 1978 · 579 bridges

Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.

All 88 Good 41 Fair 42 Poor 5

All bridges (88)

Sort:

Boise County Bridge Snapshot

Condition distribution

Boise County's Poor-condition bridges carry 220 vehicle crossings a day

46.6% of Boise County's bridges have passed the 50-year mark

One structure carries 45.5% of the county's Poor-condition bridge traffic

How Boise 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

All bridges (88)

HUNTER CK-CRKD. R.

SMA 3824;BNKS LWMN

WAPITI ROAD

SH 21

ROUGH CREEK ROAD

W. WILLOW-BIG OWL

OKEEFE CREEK ROAD

WILLOW CK.-CRKD.R.

LT. ANDERSON CK RD

PARK CK. C.G. RD.

SUMMIT FLAT ROAD

STC 3826;ALDER CRK

NFSR 347

PIONEER ROAD

SH 55

SH 21

SH 21

GRAND JEAN ROAD

SH 21

SH 21

SH 21

DEADWD.-SCT.MT.RD.

EDNA CK.-L.OWL RD.

HUNTER CK-CRKD. R.

OLD CROUCH ROAD

SH 55

SH 21

SH 21

SH 21

SH 21

BOISE STREET

GRIMES PASS ROAD

SH 21

AVELENE CK. ROAD

SHAFER CREEK ROAD

COTTONWD-BANNOCK

BOULDER CREEK ROAD

ANDERSON CREEK RD

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