County profile · official public datasets

Custer County, ID

128 public highway bridges tracked in the FHWA National Bridge Inventory: 34.4% rated Good, 56.3% Fair, 9.4% Poor.

128
Public bridges: 34.4%
Good condition: 9.4%
Poor condition

The verdict

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

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

38th
of 44 on Poor share: 9.4%
Poor-condition share: 128
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.

Custer County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Custer County ranks #38 of 44 Idaho counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 9.4%). Custer County, Idaho contains 128 public highway bridges. Roughly 34.4% are rated “Good,” 56.3% “Fair,” and 9.4% “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

128

Public highway bridges in Custer County

Good condition

34.4%

44 of 128 rated 7-9

Fair condition

56.3%

72 of 128 rated 5-6

Poor condition

9.4%

12 of 128 rated 4 or below

In-state Poor-share rank

#38 of 44

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

Condition distribution

Share of 128 NBI-tracked bridges by lowest applicable component rating.

Good

34.4% (44)

Fair

56.3% (72)

Poor

9.4% (12)

Custer County's Poor-condition bridges carry 2,050 vehicle crossings a day

That is 5.9% of the county's reported daily bridge traffic on 9.4% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 171 crossings a day against 310 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 128 of 128 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

54.7% of Custer County's bridges have passed the 50-year mark

70 of the 128 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 34.4% 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 32.2% of the county's Poor-condition bridge traffic

SH 75 over YANKEE FK OF SALMON RIVR, built 1934, carries 660 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 12-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 2,050 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1920s

1
1930s

4
1940s

2
1950s

9
1960s

33
1970s

28
1980s

17
1990s

10
2000s

7
2010s

13
2020s

4

What this shows Construction peaked in the 1960s, when 33 of the county's bridges still in the inventory were built, which is 25.8% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1978) matches the Idaho average (1979).

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

The 5 Idaho counties nearest Custer County in number of bridges, with their condition splits. Its 9.4% Poor share is the 6th-lowest of these 6. Its average build year of 1978 against a peer-group mean of 1979 is in line with the group.

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

Bridge inventory size and condition shares for Custer County and the 5 Idaho counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Fremont County	137	32.8%	61.3%	5.8%	1983
Custer County (this page)	128	34.4%	56.3%	9.4%	1978
Jefferson County	127	17.3%	79.5%	3.1%	1973
Twin Falls County	126	12.7%	84.1%	3.2%	1973
Bannock County	124	33.1%	62.1%	4.8%	1981
Cassia County	116	15.5%	84.5%	0%	1984

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

Similar inventory size

Nearest county inventories outside ID (128 bridges here).

Franklin County, ME · 128 bridges
Harper County, OK · 128 bridges
Dillon County, SC · 128 bridges
Cheatham County, TN · 128 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 128 Good 44 Fair 72 Poor 12

Fair-condition bridges (72)

Sort:

Custer County Bridge Snapshot

Condition distribution

Custer County's Poor-condition bridges carry 2,050 vehicle crossings a day

54.7% of Custer County's bridges have passed the 50-year mark

One structure carries 32.2% of the county's Poor-condition bridge traffic

How Custer 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

Fair-condition bridges (72)

FDR

BAYHORSE ROAD

NO DATA ENTERED

CAPITOL AVENUE

NO DATA ENTERED

NO DATA ENTERED

NO DATA ENTERED

HOUSTON ROAD

STC6702;SMELTER RD

CUSTER MOTORWAY

FDR

SQUAW CREEK RD

CUSTER MOTORWAY

BEAVER CREEK ROAD

FDR

FDR

FDR

SH 75

SAWMILL CANYON RD

BEAVER CREEK ROAD

SQUAW CREEK RD

EAST FORK RD

EAST FORK RD

SQ___ CREEK ROAD

BEAVER-LOON ROAD

E FORK ROAD

SH 21

SH 75

BEAVER CREEK ROAD

US 93

TREALOR CREEK ROAD

FDR

FDR

SQ___ CREEK ROAD

E FORK ROAD

KANE CREEK ROAD

ROAD

CUSTER MOTORWAY

THOMPSON CR ROAD

BEAVER-LOON ROAD

FDR

BEAVER-LOON ROAD

BEAVER-LOON ROAD

BULL CREEK ROAD

CUSTER MOTORWAY

BASIN CREEK ROAD

COPPER BASIN LOOP

BEAVER-LOON ROAD

BEAVER CREEK ROAD

CORRAL CANYON ROAD

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