County profile · official public datasets

Lewis and Clark County, MT

200 public highway bridges tracked in the FHWA National Bridge Inventory: 58% rated Good, 36.5% Fair, 5.5% Poor.

200
Public bridges
58%
Good condition
5.5%
Poor condition

The verdict

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

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

Top 48%
lowest Poor share in state
5.5%
Poor-condition share
200
public highway bridges
1979
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.

Lewis and Clark County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Lewis and Clark County ranks #27 of 56 Montana counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 5.5%). Lewis and Clark County, Montana contains 200 public highway bridges. Roughly 58% are rated “Good,” 36.5% “Fair,” and 5.5% “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

200

Public highway bridges in Lewis and Clark County

Good condition

58%

116 of 200 rated 7-9

Fair condition

36.5%

73 of 200 rated 5-6

Poor condition

5.5%

11 of 200 rated 4 or below

In-state Poor-share rank

#27 of 56

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

Condition distribution

Share of 200 NBI-tracked bridges by lowest applicable component rating.

Good
58% (116)
Fair
36.5% (73)
Poor
5.5% (11)

Lewis and Clark County's Poor-condition bridges carry 11,869 vehicle crossings a day

That is 2.8% of the county's reported daily bridge traffic on 5.5% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 1,079 crossings a day against 2,409 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 200 of 200 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

46.5% of Lewis and Clark County's bridges have passed the 50-year mark

93 of the 200 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 58% 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 62.7% of the county's Poor-condition bridge traffic

LINCOLN RD over INT LINCOLN-I 15, built 1962, carries 7,447 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 11-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 11,869 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

When Lewis and Clark County's bridges were built

200 bridges with a recorded construction year, grouped by decade

bridges

What this shows Construction peaked in the 1960s, when 46 of the county's bridges still in the inventory were built, which is 23% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1979) matches the Montana average (1977).

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

How Lewis and Clark County compares with Montana's closest counties by inventory size

The 5 Montana counties nearest Lewis and Clark County in number of bridges, with their condition splits. Its 5.5% Poor share is the 4th-lowest of these 6. Its average build year of 1979 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 Lewis and Clark County and the 5 Montana counties closest to it in inventory size
County Bridges Poor
Gallatin County 210 4.3%
Missoula County 206 7.8%
Flathead County 204 4.9%
Lewis and Clark County (this page) 200 5.5%
Lincoln County 190 14.7%
Cascade County 185 3.8%

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

Similar inventory size

Nearest county inventories outside MT (200 bridges here).

Similar average build year

Nearest mean year-built outside MT (1979 here).

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

All 200 Good 116 Fair 73 Poor 11

All bridges (200)

FIELDS GLCH ROAD

Fair

Over: POORMAN CREEK

FIELDS GULCH, Lewis and Clark, MT

Built 1979 Load: 30.8 t ADT: 20

PROSPECT AVE-US 12

Fair

Over: INT CAPITOL-I 15

HELENA-PROSPECT AVE, Lewis and Clark, MT

Built 1961 Load: 30.8 t ADT: 11,806

PROSPECT AVE-US 12

Fair

Over: INT CAPITOL-I 15

HELENA-PROSPECT AVE, Lewis and Clark, MT

Built 1961 Load: 30.8 t ADT: 11,806

LINCOLN RD W

Fair

Over: CANYON CREEK

5M NW CANYON CREEK, Lewis and Clark, MT

Built 1949 Load: 30.8 t ADT: 394

DEARBORN CANYON RD

Fair

Over: FALLS CREEK 049

2M SW BEAN LAKE, Lewis and Clark, MT

Built 1960 Load: 31.7 t ADT: 117

COUNTY ROAD 061

Fair

Over: LITTLE PRICKLY PEAR 111

1M N SIEBEN INT, Lewis and Clark, MT

Built 1962 Load: 31.8 t ADT: 13

S 21

Fair

Over: DRY CREEK 122

12M W SIMMS, Lewis and Clark, MT

Built 1935 Load: 31.8 t ADT: 258

UNKNOWN

Fair

Over: PRICKELY PEAR CREEK

5M NE HELENA, Lewis and Clark, MT

Built 1940 Load: 32.7 t ADT: 100

WYLIE DR

Fair

Over: HELENA VALLEY CANAL 081

2M N EAST HELENA, Lewis and Clark, MT

Built 1958 Load: 32.7 t ADT: 4,571

SIERRA ROAD E

Fair

Over: PRICKLY PEAR CREEK 077

5M NE HELENA, Lewis and Clark, MT

Built 1998 Load: 32.7 t ADT: 619

RIMINI RD

Fair

Over: TEN MILE CREEK 105

15M SW HELENA, Lewis and Clark, MT

Built 1981 Load: 32.7 t ADT: 230

RIMINI RD

Fair

Over: TEN MILE CREEK 106

1M S RIMINI, Lewis and Clark, MT

Built 1962 Load: 33.6 t ADT: 106

COUNTY ROAD 811

Fair

Over: TEN MILE CREEK 131

W EDGE OF HELENA, Lewis and Clark, MT

Built 2005 Load: 35.4 t ADT: 100

S 435

Fair

Over: ELK CREEK

6M SW AUGUSTA, Lewis and Clark, MT

Built 1958 Load: 36.3 t ADT: 33

I 15

Fair

Over: INT WOLF CREEK

WOLF CREEK, Lewis and Clark, MT

Built 1966 Load: 39.9 t ADT: 2,522

FRONTAGE ROAD 295

Fair

Over: TEN MILE CREEK 071

2M N HELENA, Lewis and Clark, MT

Built 1962 Load: 43.5 t ADT: 1,755

Route 284

Fair

Over: Canyon Ferry Spillway

14 mi E-NE of Helena MT, Lewis and Clark, MT

Built 1950 Load: 44.1 t ADT: 600

CEDAR ST

Fair

Over: INT CEDAR ST-I 15

HELENA-CEDAR ST, Lewis and Clark, MT

Built 2002 Load: 45.4 t ADT: 17,684

S 200

Fair

Over: FLAT CREEK

16M SW SIMMS, Lewis and Clark, MT

Built 1986 Load: 85.3 t ADT: 1,455

I 15

Fair

Over: DOG CREEK

1M S CRAIG, Lewis and Clark, MT

Built 1967 Load: 89.8 t ADT: 4,253

I 15

Fair

Over: WOLF CREEK

WOLF CREEK, Lewis and Clark, MT

Built 1966 Load: 99.9 t ADT: 5,043

S 21

Fair

Over: SPRING CREEK COULEE 124

5M E AUGUSTA, Lewis and Clark, MT

Built 1982 Load: 99.9 t ADT: 258

US 287

Fair

Over: ROCK CREEK

3M NE WOLF CREEK, Lewis and Clark, MT

Built 1967 Load: 99.9 t ADT: 561

NO DATA ENTERED

Good

Over: BEAVER CREEK

NO DATA ENTERED, Lewis and Clark, MT

Built 2019 ADT: 50

NO DATA ENTERED

Good

Over: BEAVER CREEK

NO DATA ENTERED, Lewis and Clark, MT

Built 2018 ADT: 50

LOST HORSE CR RD

Good

Over: DEADMAN CREEK 098

7M SW CANYON CREEK, Lewis and Clark, MT

Built 1990 Load: 12.7 t ADT: 100

JOHN G MINE RD

Good

Over: HELENA VALLEY CANAL 116

6M NW HELENA, Lewis and Clark, MT

Built 1958 Load: 12.7 t ADT: 790

NORRIS RD

Good

Over: HELENA VALLEY CANAL 114

4M NW HELENA, Lewis and Clark, MT

Built 1958 Load: 15.4 t ADT: 488

COUNTY ROAD 290

Good

Over: HELENA VALLEY CANAL 085

N OF HELENA AIRPORT, Lewis and Clark, MT

Built 1958 Load: 17.2 t ADT: 100

LT PRICKLY PEAR RD

Good

Over: LTL PRICKLY PEAR CR 097

6M W CANYON CREEK, Lewis and Clark, MT

Built 1952 Load: 20.0 t ADT: 121

050438: SAUERKRAUT

Good

Over: Sauerkraut Creek

4.5 mi. W of Lincoln MT, Lewis and Clark, MT

Built 2010 Load: 20.7 t ADT: 5

NFSR 233

Good

Over: WILLOW CREEK

LITTLE WILLOW CREEK, Lewis and Clark, MT

Built 2004 Load: 20.7 t ADT: 26

RIMINI RD

Good

Over: TEN MILE CREEK 101

11M W HELENA, Lewis and Clark, MT

Built 2015 Load: 21.4 t ADT: 230

NFSR 233

Good

Over: W FK BEAVER CREEK

BEAVER CREEK NO. 2, Lewis and Clark, MT

Built 1978 Load: 22.7 t ADT: 26

WYLIE DR

Good

Over: PRICKLY PEAR CREEK 080

1M N EAST HELENA, Lewis and Clark, MT

Built 1958 Load: 22.7 t ADT: 4,312

STEMPLE PASS RD

Good

Over: POORMAN CREEK 153

3M S LINCOLN, Lewis and Clark, MT

Built 2009 Load: 22.7 t ADT: 299

COPPER CREEK ROAD

Good

Over: COPPER CREEK

NO DATA ENTERED, Lewis and Clark, MT

Built 2005 Load: 23.7 t ADT: 169

ELK CREEK RD

Good

Over: ELK CREEK 043

10M SW AUGUSTA, Lewis and Clark, MT

Built 2010 Load: 24.5 t ADT: 100

COPPER CREEK ROAD

Good

Over: COPPER CREEK

NO DATA ENTERED, Lewis and Clark, MT

Built 2005 Load: 24.9 t ADT: 10

CHEVALLIER DR

Good

Over: LITTLE PRICKLY PEAR 110

5M SW SIEBEN INT, Lewis and Clark, MT

Built 2012 Load: 25.4 t ADT: 37

NFSR 233

Good

Over: M FK BEAVER CREEK

BEAVER CREEK NO. 4, Lewis and Clark, MT

Built 1978 Load: 25.6 t ADT: 26

NFSR 330

Good

Over: COPPER CREEK

COPPER CREEK, Lewis and Clark, MT

Built 2008 Load: 25.9 t ADT: 169

I 15

Good

Over: LITTLE PRICKLY PEAR CR

9M S WOLF CREEK, Lewis and Clark, MT

Built 1965 Load: 25.9 t ADT: 2,383

LITTLE WOLF CR RD

Good

Over: WOLF CREEK 145

7M NW WOLF CREEK, Lewis and Clark, MT

Built 2007 Load: 26.3 t ADT: 128

S 200

Good

Over: MIDDLE FK DEARBORN RIVER

25M NE LINCOLN, Lewis and Clark, MT

Built 1993 Load: 26.3 t ADT: 1,356

BARR CREEK RD

Good

Over: N FORK WILLOW CREEK 125

9M NW AUGUSTA, Lewis and Clark, MT

Built 1991 Load: 27.2 t ADT: 100

LITTLE WOLF CR RD

Good

Over: WOLF CREEK 112

4M NW WOLF CREEK, Lewis and Clark, MT

Built 2010 Load: 28.1 t ADT: 128

FRONTAGE ROAD 241

Good

Over: LITTLE PRICKLY PEAR 059

WOLF CREEK, Lewis and Clark, MT

Built 1966 Load: 28.1 t ADT: 707

STEMPLE PASS RD

Good

Over: POORMAN CREEK 140

4M S LINCOLN, Lewis and Clark, MT

Built 2007 Load: 28.1 t ADT: 95

SPRING CREEK LN

Good

Over: SPRING CREEK 152

LINCOLN, Lewis and Clark, MT

Built 2010 Load: 28.1 t ADT: 100

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

Related

Browse all → | Rankings →
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.