Total bridges
200
Public highway bridges in Lewis and Clark County
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.
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
- pre-1900 2
Built before 1900
2 bridges
- 1900s 2
1900–1909
2 bridges
- 1910s 3
1910–1919
3 bridges
- 1920s 1
1920–1929
1 bridges
- 1930s 9
1930–1939
9 bridges
- 1940s 8
1940–1949
8 bridges
- 1950s
1950–1959
19 bridges
- 1960s
1960–1969
46 bridges
- 1970s 16
1970–1979
16 bridges
- 1980s 12
1980–1989
12 bridges
- 1990s 11
1990–1999
11 bridges
- 2000s
2000–2009
42 bridges
- 2010s
2010–2019
24 bridges
- 2020s 5
2020–2029
5 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).
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.
| 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.
Fair-condition bridges (73)
FIELDS GLCH ROAD
FairOver: POORMAN CREEK
FIELDS GULCH, Lewis and Clark, MT
Built 1979 Load: 30.8 t ADT: 20
PROSPECT AVE-US 12
FairOver: INT CAPITOL-I 15
HELENA-PROSPECT AVE, Lewis and Clark, MT
Built 1961 Load: 30.8 t ADT: 11,806
PROSPECT AVE-US 12
FairOver: INT CAPITOL-I 15
HELENA-PROSPECT AVE, Lewis and Clark, MT
Built 1961 Load: 30.8 t ADT: 11,806
LINCOLN RD W
FairOver: CANYON CREEK
5M NW CANYON CREEK, Lewis and Clark, MT
Built 1949 Load: 30.8 t ADT: 394
DEARBORN CANYON RD
FairOver: FALLS CREEK 049
2M SW BEAN LAKE, Lewis and Clark, MT
Built 1960 Load: 31.7 t ADT: 117
COUNTY ROAD 061
FairOver: LITTLE PRICKLY PEAR 111
1M N SIEBEN INT, Lewis and Clark, MT
Built 1962 Load: 31.8 t ADT: 13
S 21
FairOver: DRY CREEK 122
12M W SIMMS, Lewis and Clark, MT
Built 1935 Load: 31.8 t ADT: 258
UNKNOWN
FairOver: PRICKELY PEAR CREEK
5M NE HELENA, Lewis and Clark, MT
Built 1940 Load: 32.7 t ADT: 100
WYLIE DR
FairOver: HELENA VALLEY CANAL 081
2M N EAST HELENA, Lewis and Clark, MT
Built 1958 Load: 32.7 t ADT: 4,571
SIERRA ROAD E
FairOver: PRICKLY PEAR CREEK 077
5M NE HELENA, Lewis and Clark, MT
Built 1998 Load: 32.7 t ADT: 619
RIMINI RD
FairOver: TEN MILE CREEK 105
15M SW HELENA, Lewis and Clark, MT
Built 1981 Load: 32.7 t ADT: 230
RIMINI RD
FairOver: TEN MILE CREEK 106
1M S RIMINI, Lewis and Clark, MT
Built 1962 Load: 33.6 t ADT: 106
COUNTY ROAD 811
FairOver: TEN MILE CREEK 131
W EDGE OF HELENA, Lewis and Clark, MT
Built 2005 Load: 35.4 t ADT: 100
S 435
FairOver: ELK CREEK
6M SW AUGUSTA, Lewis and Clark, MT
Built 1958 Load: 36.3 t ADT: 33
I 15
FairOver: INT WOLF CREEK
WOLF CREEK, Lewis and Clark, MT
Built 1966 Load: 39.9 t ADT: 2,522
FRONTAGE ROAD 295
FairOver: TEN MILE CREEK 071
2M N HELENA, Lewis and Clark, MT
Built 1962 Load: 43.5 t ADT: 1,755
Route 284
FairOver: Canyon Ferry Spillway
14 mi E-NE of Helena MT, Lewis and Clark, MT
Built 1950 Load: 44.1 t ADT: 600
CEDAR ST
FairOver: INT CEDAR ST-I 15
HELENA-CEDAR ST, Lewis and Clark, MT
Built 2002 Load: 45.4 t ADT: 17,684
S 200
FairOver: FLAT CREEK
16M SW SIMMS, Lewis and Clark, MT
Built 1986 Load: 85.3 t ADT: 1,455
I 15
FairOver: DOG CREEK
1M S CRAIG, Lewis and Clark, MT
Built 1967 Load: 89.8 t ADT: 4,253
I 15
FairOver: WOLF CREEK
WOLF CREEK, Lewis and Clark, MT
Built 1966 Load: 99.9 t ADT: 5,043
S 21
FairOver: SPRING CREEK COULEE 124
5M E AUGUSTA, Lewis and Clark, MT
Built 1982 Load: 99.9 t ADT: 258
US 287
FairOver: ROCK CREEK
3M NE WOLF CREEK, Lewis and Clark, MT
Built 1967 Load: 99.9 t ADT: 561
Read our methodology - how this data is sourced, computed, and verified.
Related
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.