County profile · official public datasets

Yellowstone County, MT

290 public highway bridges tracked in the FHWA National Bridge Inventory: 31.7% rated Good, 66.2% Fair, 2.1% Poor.

290
Public bridges: 31.7%
Good condition: 2.1%
Poor condition

The verdict

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

Yellowstone County posts a top-quartile lowest Poor-condition share among rated counties in the state across mid-size county bridge inventory.

Top 13%
lowest Poor share in state: 2.1%
Poor-condition share: 290
public highway bridges: 1980
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.

Yellowstone County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Yellowstone County ranks #7 of 56 Montana counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 2.1%). Yellowstone County, Montana contains 290 public highway bridges. Roughly 31.7% are rated “Good,” 66.2% “Fair,” and 2.1% “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

290

Public highway bridges in Yellowstone County

Good condition

31.7%

92 of 290 rated 7-9

Fair condition

66.2%

192 of 290 rated 5-6

Poor condition

2.1%

6 of 290 rated 4 or below

In-state Poor-share rank

#7 of 56

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

Condition distribution

Share of 290 NBI-tracked bridges by lowest applicable component rating.

Good

31.7% (92)

Fair

66.2% (192)

Poor

2.1% (6)

Yellowstone County's Poor-condition bridges carry 25,421 vehicle crossings a day

That is 2.3% of the county's reported daily bridge traffic on 2.1% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 4,237 crossings a day against 2,729 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 290 of 290 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

45.5% of Yellowstone County's bridges have passed the 50-year mark

132 of the 290 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 31.7% 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 33% of the county's Poor-condition bridge traffic

MONTANA AVE over U1025-RR, built 1960, carries 8,399 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 25,421 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1920s

4
1930s

8
1940s

9
1950s

12
1960s

78
1970s

52
1980s

26
1990s

31
2000s

39
2010s

21
2020s

10

What this shows Construction peaked in the 1960s, when 78 of the county's bridges still in the inventory were built, which is 26.9% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1980) matches the Montana average (1977).

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

The 5 Montana counties nearest Yellowstone County in number of bridges, with their condition splits. Its 2.1% Poor share is the 1st-lowest of these 6. Its average build year of 1980 against a peer-group mean of 1979 is in line with the group.

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

Bridge inventory size and condition shares for Yellowstone County and the 5 Montana counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Yellowstone County (this page)	290	31.7%	66.2%	2.1%	1980
Beaverhead County	226	23.9%	66.8%	9.3%	1978
Gallatin County	210	19%	76.7%	4.3%	1977
Missoula County	206	33.5%	58.7%	7.8%	1976
Flathead County	204	30.9%	64.2%	4.9%	1983
Lewis and Clark County	200	58%	36.5%	5.5%	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 Yellowstone 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 Yellowstone County, both outside Montana so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside MT (290 bridges here).

Knox County, IN · 290 bridges
Putnam County, IN · 290 bridges
Monroe County, MS · 290 bridges
Outagamie County, WI · 290 bridges

Similar average build year

Nearest mean year-built outside MT (1980 here).

Tulsa County, OK · avg 1980 · 1,135 bridges
Miami-Dade County, FL · avg 1980 · 1,057 bridges
Pulaski County, AR · avg 1980 · 721 bridges
McLennan County, TX · avg 1980 · 714 bridges

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

All 290 Good 92 Fair 192 Poor 6

Fair-condition bridges (192)

Sort:

Yellowstone County Bridge Snapshot

Condition distribution

Yellowstone County's Poor-condition bridges carry 25,421 vehicle crossings a day

45.5% of Yellowstone County's bridges have passed the 50-year mark

One structure carries 33% of the county's Poor-condition bridge traffic

How Yellowstone 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 (192)

KING AVE W

I 90

I 90

I 94

I 94

I 94

I 94

I 94

I 94

DUCK CREEK RD

OLD HWY 312

S BILLINGS BLVD

S FRONTAGE RD

I 90

I 94

I 94

SHANNON RD

DANFORD RD

TREWIN SCHOOL RD

SHEPHERD ACTON RD

S BILLINGS BLVD

BUNDY RD

I 90

I 90

I 90

I 90

I 90

I 94

I 94

I 94

I 94

I 94

I 94

N 18TH RD

N 19TH RD

LOWER CANAL RD

FLY CREEK RD

PRYOR RD

PRYOR RD

PRYOR RD

AQUI ESTA DR

COLLEEN DR

56TH ST W

CANYON CREEK RD

MARKEGARD RD

ROLAND DR

S 44TH ST W

ESTHER ROSE LN

ALKALI CREEK RD

SHAMROCK DR

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