County profile · official public datasets

Granite County, MT

73 public highway bridges tracked in the FHWA National Bridge Inventory: 37% rated Good, 52.1% Fair, 11% Poor.

73
Public bridges
37%
Good condition
11%
Poor condition

The verdict

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

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

47th
of 56 on Poor share
11%
Poor-condition share
73
public highway bridges
1974
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.

Granite County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Granite County ranks #47 of 56 Montana counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 11%). Granite County, Montana contains 73 public highway bridges. Roughly 37% are rated “Good,” 52.1% “Fair,” and 11% “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

73

Public highway bridges in Granite County

Good condition

37%

27 of 73 rated 7-9

Fair condition

52.1%

38 of 73 rated 5-6

Poor condition

11%

8 of 73 rated 4 or below

In-state Poor-share rank

#47 of 56

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

Condition distribution

Share of 73 NBI-tracked bridges by lowest applicable component rating.

Good
37% (27)
Fair
52.1% (38)
Poor
11% (8)

Granite County's Poor-condition bridges carry 14,360 vehicle crossings a day

That is 10.3% of the county's reported daily bridge traffic on 11% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 1,795 crossings a day against 2,189 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 73 of 73 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

61.6% of Granite County's bridges have passed the 50-year mark

45 of the 73 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 37% 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 83.4% of the county's Poor-condition bridge traffic

I 90 over CLARK FORK RIVER, built 1970, carries 11,980 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 8-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 14,360 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

When Granite County's bridges were built

73 bridges with a recorded construction year, grouped by decade

bridges

What this shows Construction peaked in the 1960s, when 20 of the county's bridges still in the inventory were built, which is 27.4% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1974) matches the Montana average (1977).

Source FHWA National Bridge Inventory (year built) As of 2024 NBI release

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

The 5 Montana counties nearest Granite County in number of bridges, with their condition splits. Its 11% Poor share is the 6th-lowest of these 6. Its average build year of 1974 against a peer-group mean of 1976 is in line with the group.

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

Bridge inventory size and condition shares for Granite County and the 5 Montana counties closest to it in inventory size
County Bridges Poor
Carbon County 80 5%
Granite County (this page) 73 11%
Custer County 71 1.4%
Glacier County 71 5.6%
Deer Lodge County 68 5.9%
Silver Bow County 68 1.5%

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

Similar inventory size

Nearest county inventories outside MT (73 bridges here).

Similar average build year

Nearest mean year-built outside MT (1974 here).

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

All 73 Good 27 Fair 38 Poor 8

All bridges (73)

MT 38-SKALKAHO RD

Good

Over: W FORK ROCK CREEK 012

12M E SKALKAHO PASS, Granite, MT

Built 1974 Load: 32.7 t ADT: 219

UPPER ROCK CR RD

Good

Over: ROCK CREEK 010

20M W PHILLIPSBURG, Granite, MT

Built 1976 Load: 32.7 t ADT: 592

NO DATA ENTERED

Good

Over: MEADOW CR

BEGINNING OF MCDOUGAL RD, Granite, MT

Built 1978 Load: 35.3 t ADT: 40

ROCK CREEK ROAD

Good

Over: COUGAR CREEK

T08N R17W S07, Granite, MT

Built 2008 Load: 36.3 t ADT: 40

I 90

Good

Over: INT BEARMOUTH

BEARMOUTH, Granite, MT

Built 1970 Load: 37.2 t ADT: 5,990

HENDERSON CREEK RO

Good

Over: FLINT CREEK 035

11M S DRUMMOND, Granite, MT

Built 2013 Load: 37.2 t ADT: 100

DOUGLAS CREEK ROAD

Good

Over: FLINT CREEK 004

8M S DRUMMOND, Granite, MT

Built 2015 Load: 38.1 t ADT: 100

ROAD 358

Good

Over: HARVEY CREEK

HARVEY CREEK, Granite, MT

Built 1984 Load: 38.2 t ADT: 40

I 90

Good

Over: SEP EDWARDS GULCH ROAD

DRUMMOND, Granite, MT

Built 1966 Load: 40.8 t ADT: 4,305

I 90

Good

Over: SEP EDWARDS GULCH ROAD

DRUMMOND, Granite, MT

Built 1966 Load: 40.8 t ADT: 4,305

CABLE MTN CAMPGROU

Good

Over: N FK FLINT CREEK

NO DATA ENTERED, Granite, MT

Built 2015 Load: 41.8 t ADT: 40

I 90

Good

Over: HARVEY CREEK

3M E BEARMOUTH INT, Granite, MT

Built 1970 Load: 53.5 t ADT: 11,980

I 90

Good

Over: RATTLER GULCH

4.1M W DRUMMOND, Granite, MT

Built 1971 Load: 57.2 t ADT: 11,980

MOOSE LAKE RD

Good

Over: E FORK ROCK CREEK 030

10M SW PORTERS CORNER, Granite, MT

Built 1950 Load: 74.4 t ADT: 183

I 90

Good

Over: DRAINAGE

4.8M E BEARMOUTH INT, Granite, MT

Built 1971 Load: 99.9 t ADT: 11,980

NO DATA ENTERED

Poor

Over: BOULDER CR

BOULDER CREEK, Granite, MT

Built 1949 Load: 19.1 t ADT: 50

NO DATA ENTERED

Poor

Over: SWAMP GUL

SWAMP GULCH, Granite, MT

Built 1987 Load: 27.2 t ADT: 50

MARSHALL CREEK RD

Poor

Over: ROCK CREEK

14M W PHILIPSBURG, Granite, MT

Built 1959 Load: 27.2 t ADT: 158

BEAR GULCH RD

Poor

Over: CLARK FORK RIVER 002

1M NE BEARMOUTH, Granite, MT

Built 1986 Load: 29.9 t ADT: 128

I 90

Poor

Over: CLARK FORK RIVER

5M W DRUMMOND, Granite, MT

Built 1970 Load: 31.8 t ADT: 11,980

S MAIN STREET

Poor

Over: CLARK FORK RIVER 020

S DRUMMOND, Granite, MT

Built 1934 Load: 34.5 t ADT: 565

S 1

Poor

Over: CLARK FORK

DRUMMOND, Granite, MT

Built 1966 Load: 37.2 t ADT: 1,329

I 90

Poor

Over: ANTELOPE CREEK

11.2M W DRUMMOND, Granite, MT

Built 1971 Load: 39.0 t ADT: 100

Read our methodology - how this data is sourced, computed, and verified.

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Data sourced from official public datasets. See our methodology for details. Retrieved and formatted by PlainBridges

Every figure on PlainBridges is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. NBI condition categories reflect the latest reported inventory record, not a live safety, closure, or travel decision.