County profile · official public datasets

Petroleum County, MT

26 public highway bridges tracked in the FHWA National Bridge Inventory: 30.8% rated Good, 53.8% Fair, 15.4% Poor.

Compiled by PlainBridges

26
Public bridges: 30.8%
Good condition: 15.4%
Poor condition

The verdict

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

Petroleum County pairs a higher-than-median Poor-condition share among rated counties in the state with an older average build year than the state inventory.

53rd
of 56 on Poor share: 15.4%
Poor-condition share: 26
public highway bridges: 1967
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.

Petroleum County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Petroleum County ranks #53 of 56 Montana counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 15.4%). Petroleum County, Montana contains 26 public highway bridges. Roughly 30.8% are rated “Good,” 53.8% “Fair,” and 15.4% “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

26

Public highway bridges in Petroleum County

Good condition

30.8%

8 of 26 rated 7-9

Fair condition

53.8%

14 of 26 rated 5-6

Poor condition

15.4%

4 of 26 rated 4 or below

In-state Poor-share rank

#53 of 56

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

Condition distribution

Share of 26 NBI-tracked bridges by lowest applicable component rating.

Good

30.8% (8)

Fair

53.8% (14)

Poor

15.4% (4)

Petroleum County's Poor-condition bridges carry 434 vehicle crossings a day

That is 12.5% of the county's reported daily bridge traffic on 15.4% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 109 crossings a day against 78 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 26 of 26 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

57.7% of Petroleum County's bridges have passed the 50-year mark

15 of the 26 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 30.8% 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 53.5% of the county's Poor-condition bridge traffic

S 244 over YELLOW WATER CR-ELK CR, built 1948, carries 232 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 4-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 434 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1930s

4
1940s

5
1950s

2
1960s

4
1970s

3
1980s

3
1990s

1
2010s

3
2020s

1

What this shows Construction peaked in the 1940s, when 5 of the county's bridges still in the inventory were built, which is 19.2% of those with a recorded year. That cohort is now 75 to 84 years old in the 2024 inventory. Its average build year is 1967, 10 years older than the Montana average of 1977.

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

The 5 Montana counties nearest Petroleum County in number of bridges, with their condition splits. Its 15.4% Poor share is the 6th-lowest of these 6. Its average build year of 1967 against a peer-group mean of 1977 is 10 years older.

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

Bridge inventory size and condition shares for Petroleum County and the 5 Montana counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Musselshell County	28	57.1%	39.3%	3.6%	1986
Garfield County	26	38.5%	57.7%	3.8%	1989
Treasure County	26	34.6%	50%	15.4%	1966
Wheatland County	26	30.8%	61.5%	7.7%	1967
Petroleum County (this page)	26	30.8%	53.8%	15.4%	1967
Wibaux County	25	12%	84%	4%	1975

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

Similar inventory size

Nearest county inventories outside MT (26 bridges here).

Mineral County, CO · 26 bridges
Webster County, GA · 26 bridges
St. James County, LA · 26 bridges
Deaf Smith County, TX · 26 bridges

Similar average build year

Nearest mean year-built outside MT (1967 here).

Los Angeles County, CA · avg 1967 · 3,547 bridges
Allegheny County, PA · avg 1967 · 1,294 bridges
Sonoma County, CA · avg 1967 · 609 bridges
Merced County, CA · avg 1967 · 528 bridges

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

All 26 Good 8 Fair 14 Poor 4

All bridges (26)

Sort:

PETROLIA BENCH RD

Over: MCDONALD CREEK 003

9M E WINNETT, Petroleum, MT

Built 1940 Load: 5.4 t ADT: 58

MAIN ST

Over: MCDONALD CREEK 015

WINNETT-MAIN ST, Petroleum, MT

Built 1940 Load: 5.4 t ADT: 98

TEIGEN LOOP

Over: MCDONALD CREEK 032

S TEIGEN, Petroleum, MT

Built 2012 Load: 9.1 t ADT: 100

CEMETARY RD

Over: SO FK BUFFALO CR 011

6M NW WINNETT, Petroleum, MT

Built 1960 Load: 11.8 t ADT: 100

S 244

Over: FLATWILLOW CREEK

6M SW FLATWILLOW, Petroleum, MT

Built 1939 Load: 21.8 t ADT: 207

DOVETAIL VALENTINE

Over: BUFFALO CREEK 006

6M N WINNETT, Petroleum, MT

Built 1983 Load: 22.7 t ADT: 100

S 244

Over: DRAINAGE

10M SW FLATWILLOW, Petroleum, MT

Built 1940 Load: 22.7 t ADT: 207

S 244

Over: MCDONALD CREEK

WINNETT, Petroleum, MT

Built 1941 Load: 22.7 t ADT: 244

S 244

Over: PIKE CREEK

FLATWILLOW, Petroleum, MT

Built 1939 Load: 23.6 t ADT: 232

S 244

Over: DRAINAGE

FLATWILLOW, Petroleum, MT

Built 1935 Load: 23.6 t ADT: 232

ROAD 317

Over: ALKALI CREEK

SECT 1 T18N R29E, Petroleum, MT

Built 1963 Load: 24.5 t ADT: 2

S 200

Over: BOX ELDER CREEK

8M E WINNETT, Petroleum, MT

Built 1953 Load: 29.9 t ADT: 630

PETROLIA LAKE RD

Over: MCDONALD CREEK 014

6M E WINNETT, Petroleum, MT

Built 1980 Load: 32.7 t ADT: 100

BLAKESLEE RD

Over: CANAL 030

7M N TEIGEN, Petroleum, MT

Built 1978 Load: 32.7 t ADT: 100

Flatwillow Road

Over: Flatwilow Creek

12M S Winnett, Petroleum, MT

Built 2023 ADT: 100

DOVETAIL VALENTINE

Over: BOX ELDER CREEK 007

6M N WINNETT, Petroleum, MT

Built 1982 Load: 20.9 t ADT: 100

WELTER DIVIDE RD

Over: BOX ELDER CREEK 010

13M NE TEIGEN, Petroleum, MT

Built 1994 Load: 25.4 t ADT: 100

S 500

Over: FLATWILLOW CREEK

6M SW MOSBY, Petroleum, MT

Built 1962 Load: 26.3 t ADT: 31

S 500

Over: NORTH WILLOW CREEK

13M SW MOSBY, Petroleum, MT

Built 1975 Load: 27.2 t ADT: 33

WILDHORSE RD

Over: BOX ELDER CREEK 012

13M NW WINNETT, Petroleum, MT

Built 1978 Load: 32.7 t ADT: 100

KELLY RD

Over: FLATWILLOW CREEK 013

8M S WINNETT, Petroleum, MT

Built 2013 Load: 34.3 t ADT: 58

HORSE CAMP ROAD

Over: SACAGAWEA RIVER

38 MILES NORTH OF WINNETT, Petroleum, MT

Built 2015 Load: 37.2 t ADT: 100

OLD CAT CREEK RD

Over: BOX ELDER CREEK 008

5M NE WINNETT, Petroleum, MT

Built 1930 Load: 5.4 t ADT: 100

HUGHES LN

Over: FLATWILLOW CREEK 016

16M S WINNETT, Petroleum, MT

Built 1950 Load: 10.0 t ADT: 100

ROAD 317

Over: DRAG CREEK

SECT 11 T18N R29E, Petroleum, MT

Built 1963 Load: 20.9 t ADT: 2

S 244

Over: YELLOW WATER CR-ELK CR

5M S WINNETT, Petroleum, MT

Built 1948 Load: 29.9 t ADT: 232

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

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Compiled by PlainBridges, Independent data publisher

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.