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.

pre-1900

2
1900s

2
1910s

3
1920s

1
1930s

9
1940s

8
1950s

19
1960s

46
1970s

16
1980s

12
1990s

11
2000s

42
2010s

24
2020s

5

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).

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	Good	Fair	Poor	Avg. built
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 (this page)	200	58%	36.5%	5.5%	1979
Lincoln County	190	38.4%	46.8%	14.7%	1977
Cascade County	185	41.6%	54.6%	3.8%	1965

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).

Escambia County, AL · 200 bridges
Clay County, AR · 200 bridges
Parke County, IN · 200 bridges
Fayette County, KY · 200 bridges

Similar average build year

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

Pima County, AZ · avg 1979 · 1,150 bridges
Jefferson County, KY · avg 1979 · 662 bridges
Spartanburg County, SC · avg 1979 · 638 bridges
McPherson County, KS · avg 1979 · 586 bridges

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)

Sort:

Lewis and Clark County Bridge Snapshot

Condition distribution

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

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

One structure carries 62.7% of the county's Poor-condition bridge traffic

How Lewis and Clark 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

All bridges (200)

BIRDTAIL RD

AUGUSTA RD

CHEVALLIER DR

MCDONALD LN

AUGUSTA-CLEMONS RD

S HOWIE ST

HEAD LN

HART LN

I 15

S 200

MINNEHAHA ROAD

US 287

BEAVER CREEK ROAD

HOGUM CK ROAD

HOGUM CK ROAD

YORK RD

SUCKER KP KL ROAD

US 287

N MONTANA AVE

I 15

I 15

NFSR 330

I 15

APPLEGATE DR

S CRUSE AVE

I 15

CRAIG FRONTAGE RD

S 200

LINCOLN RD W

LINCOLN RD W

NELSON RD

S RECREATION RD

LAKE HELENA DR

GLASS DR

STEMPLE PASS RD

BEAVER CREEK RD

WOODBRIDGE DRIVE

S 435

BANNER CREEK RD

I 15

COUNTY ROAD 061

US 287

I 15

NFSR 233

I 15

I 15

S 21

YORK RD

CRAIG FRONTAGE RD

E MAIN STREET

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