County profile · official public datasets

Big Horn County, MT

135 public highway bridges tracked in the FHWA National Bridge Inventory: 26.7% rated Good, 68.1% Fair, 5.2% Poor.

135
Public bridges: 26.7%
Good condition: 5.2%
Poor condition

The verdict

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

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

Top 38%
lowest Poor share in state: 5.2%
Poor-condition share: 135
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.

Big Horn County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Big Horn County ranks #21 of 56 Montana counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 5.2%). Big Horn County, Montana contains 135 public highway bridges. Roughly 26.7% are rated “Good,” 68.1% “Fair,” and 5.2% “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

135

Public highway bridges in Big Horn County

Good condition

26.7%

36 of 135 rated 7-9

Fair condition

68.1%

92 of 135 rated 5-6

Poor condition

5.2%

7 of 135 rated 4 or below

In-state Poor-share rank

#21 of 56

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

Condition distribution

Share of 135 NBI-tracked bridges by lowest applicable component rating.

Good

26.7% (36)

Fair

68.1% (92)

Poor

5.2% (7)

Big Horn County's Poor-condition bridges carry 991 vehicle crossings a day

That is 0.6% of the county's reported daily bridge traffic on 5.2% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 142 crossings a day against 790 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 135 of 135 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

43% of Big Horn County's bridges have passed the 50-year mark

58 of the 135 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 26.7% 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 56.6% of the county's Poor-condition bridge traffic

OLD HWY 87 over TWO LEGGINS CANAL 0, built 1931, carries 561 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 7-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 991 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1930s

4
1940s

5
1950s

16
1960s

8
1970s

33
1980s

42
1990s

12
2000s

6
2010s

5
2020s

4

What this shows Construction peaked in the 1980s, when 42 of the county's bridges still in the inventory were built, which is 31.1% of those with a recorded year. That cohort is now 35 to 44 years old in the 2024 inventory. Its average build year (1978) matches the Montana average (1977).

How Big Horn County compares with Montana's closest counties by inventory size

The 5 Montana counties nearest Big Horn County in number of bridges, with their condition splits. Its 5.2% Poor share is the 1st-lowest of these 6. Its average build year of 1978 against a peer-group mean of 1977 is in line with the group.

Showing the 5 closest of 55 Montana counties eligible for comparison.

Bridge inventory size and condition shares for Big Horn County and the 5 Montana counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Mineral County	152	25.7%	64.5%	9.9%	1971
Ravalli County	148	41.2%	53.4%	5.4%	1981
Big Horn County (this page)	135	26.7%	68.1%	5.2%	1978
Jefferson County	134	17.9%	76.9%	5.2%	1977
Park County	124	21%	68.5%	10.5%	1976
Sanders County	120	40%	52.5%	7.5%	1979

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 Big Horn 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 Big Horn County, both outside Montana so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside MT (135 bridges here).

Nevada County, CA · 135 bridges
Meriwether County, GA · 135 bridges
Steuben County, IN · 135 bridges
Warren County, IN · 135 bridges

Similar average build year

Nearest mean year-built outside MT (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 135 Good 36 Fair 92 Poor 7

Fair-condition bridges (92)

Sort:

Big Horn County Bridge Snapshot

Condition distribution

Big Horn County's Poor-condition bridges carry 991 vehicle crossings a day

43% of Big Horn County's bridges have passed the 50-year mark

One structure carries 56.6% of the county's Poor-condition bridge traffic

How Big Horn County compares with Montana'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 (92)

COUNTY ROAD 143

UPPER RD

IRR - I 90

IRR BIA RTE 14

IRR - I 90

PINE RIDGE RD

SARPY BASIN RD

IRR - I 90

FLY CREEK RD

BALA ST

IRR - S 313

IRR - I 90

LITTLE HORN RD

IRR - I 90

IRR BIA RTE 16

IRR - I 90

IRR - I 90

IRR - I 90

IRR - I 90

IRR - I 90

IRR - S 314

SARPY CREEK RD

IRR BIA RTE 91

IRR BIA RTE 205

IRR - S 313

SARPY BASIN RD

I 90

I 90

IRR - I 90

IRR - I 90

IRR - I 90

IRR - I 90

IRR - I 90

WARMAN LOOP

IRR - S 313

IRR - I 90

IRR - I 90

IRR - I 90

IRR - I 90

IRR - I 90

IRR - S 73

IRR-S 47

FORTY MILE RD

IRR - FRONTAGE 315

IRR - US 212

IRR-S 47-3RD ST E

IRR - S 451

IRR - I 90

IRR - I 90

TULLOCK CR RD

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