County profile · official public datasets

Bannock County, ID

124 public highway bridges tracked in the FHWA National Bridge Inventory: 33.1% rated Good, 62.1% Fair, 4.8% Poor.

124
Public bridges: 33.1%
Good condition: 4.8%
Poor condition

The verdict

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

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

23rd
of 44 on Poor share: 4.8%
Poor-condition share: 124
public highway bridges: 1981
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.

Bannock County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Bannock County ranks #23 of 44 Idaho counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 4.8%). Bannock County, Idaho contains 124 public highway bridges. Roughly 33.1% are rated “Good,” 62.1% “Fair,” and 4.8% “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

124

Public highway bridges in Bannock County

Good condition

33.1%

41 of 124 rated 7-9

Fair condition

62.1%

77 of 124 rated 5-6

Poor condition

4.8%

6 of 124 rated 4 or below

In-state Poor-share rank

#23 of 44

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

Condition distribution

Share of 124 NBI-tracked bridges by lowest applicable component rating.

Good

33.1% (41)

Fair

62.1% (77)

Poor

4.8% (6)

Bannock County's Poor-condition bridges carry 27,300 vehicle crossings a day

That is 3.4% of the county's reported daily bridge traffic on 4.8% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 4,550 crossings a day against 6,510 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 124 of 124 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

54.8% of Bannock County's bridges have passed the 50-year mark

68 of the 124 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 33.1% 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 28.4% of the county's Poor-condition bridge traffic

I 15 NBL over MAIN STREET GS, built 1962, carries 7,750 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 6-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 27,300 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1920s

1
1940s

4
1950s

10
1960s

43
1970s

16
1980s

8
1990s

6
2000s

8
2010s

18
2020s

10

What this shows Construction peaked in the 1960s, when 43 of the county's bridges still in the inventory were built, which is 34.7% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1981) matches the Idaho average (1979).

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

The 5 Idaho counties nearest Bannock County in number of bridges, with their condition splits. Its 4.8% Poor share is the 5th-lowest of these 6. Its average build year of 1981 against a peer-group mean of 1977 is in line with the group.

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

Bridge inventory size and condition shares for Bannock County and the 5 Idaho counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Custer County	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 (this page)	124	33.1%	62.1%	4.8%	1981
Cassia County	116	15.5%	84.5%	0%	1984
Latah County	115	35.7%	64.3%	0%	1978

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

Similar inventory size

Nearest county inventories outside ID (124 bridges here).

Breathitt County, KY · 124 bridges
Caldwell County, LA · 124 bridges
St. Mary County, LA · 124 bridges
Bollinger County, MO · 124 bridges

Similar average build year

Nearest mean year-built outside ID (1981 here).

Franklin County, OH · avg 1981 · 922 bridges
Greenville County, SC · avg 1981 · 635 bridges
Montgomery County, OH · avg 1981 · 632 bridges
McLean County, IL · avg 1981 · 624 bridges

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

All 124 Good 41 Fair 77 Poor 6

All bridges (124)

Sort:

Bannock County Bridge Snapshot

Condition distribution

Bannock County's Poor-condition bridges carry 27,300 vehicle crossings a day

54.8% of Bannock County's bridges have passed the 50-year mark

One structure carries 28.4% of the county's Poor-condition bridge traffic

How Bannock 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 (124)

I 15 SBL

US 30

US 91

US 91

STP 7181;GOULD ST

I 15 NBL

I 15 SBL

PHILBIN ROAD

I 15 SBL

I 15 NBL

I 15 SBL

I 15 NBL

I 15 SBL

I 15 NBL

I 15B;JENSEN ROAD

US 30

I 86 EBL

CLARK STREET

STP 7181;GOULD ST

STP 7181;GOULD ST

US 30

US 30B

I 86 EBL

COTTONWOOD ROAD

US 30

I 15 NBL

I 15 SBL

SYMONS ROAD

BROXON ROAD

STC1727;PHILBIN

S. RAYMOND ROAD

MONTE VISTA DRIVE

I 15 NBL

I 15 SBL

STC 1759; BLAZER

I 15 NBL

I 15 NBL

STC7221;CARSON ST

ROSS FORK RD

I 15 NBL

2-1/2 MILE ROAD

SMA7217;S. VALLEY

I 15 NBL

I 15 SBL

I 86 WBL

STC 1760; MAIN ST

I 15 NBL

I 15 SBL

IRR BIA RTE 68

US 91 SBL

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